Tree Physiology - recent issues

Genetic and environmental variation in spring and autumn phenology of biomass willows (Salix spp.): effects on shoot growth and nitrogen economy

Weih, M. — Thu, 12 Nov 2009 00:17:46 PST

Six commercial willow (Salix spp.) varieties were examined to investigate the effects of genotype and environment on spring and autumn phenology and the relationships between phenology, shoot growth and leaf nitrogen (N) retranslocation. The willows were field-grown under different irrigation and fertilization in central Sweden. Two independent data sets of bud-burst, leaf unfolding duration, growth cessation and the timing of leaf abscission were assessed, and the biomass and leaf N data from the end of the first cutting cycle were used. Specific hypotheses were that (1) spring phenology has a greater effect on the shoot biomass production than autumn phenology; (2) later bud-burst is associated with more rapid leaf unfolding; (3) the timing of leaf abscission has a greater effect on the shoot biomass production than height growth cessation; and (4) later leaf fall is associated with poorer leaf N retranslocation. Bud-burst date varied by 19 and 39 days in the 2 years and leaf unfolding duration varied by 13 and 38 days. Growth cessation varied by 2.5 weeks and completion of leaf abscission (> 90% of leaves shed) by more than 3 weeks between the genotypes and treatments. Bud-burst date was inversely correlated with leaf unfolding duration (R² = 0.96). Significant effects of the duration of leafy period (bud-burst to leaf abscission) and bud-burst date on shoot growth were found. Delayed growth cessation and leaf abscission were generally associated with a greater biomass production, but especially the relationship between growth cessation and biomass was weak. The results show that the timing of bud-burst and leaf abscission is more important for willow biomass production than growth cessation. Delayed leaf abscission has a negative effect on leaf N retranslocation and increases the N losses. The results have implications for the breeding of perennial energy crops.

Coupling tree-ring {delta}13C and {delta}15N to test the effect of fertilization on mature Douglas-fir (Pseudotsuga menziesii var. glauca) stands across the Interior northwest, USA

Balster, N. J., Marshall, J. D., Clayton, M. — Thu, 12 Nov 2009 00:17:46 PST

Nitrogen (N) fertilization causes long-term increases in biomass production in many N-limited forests around the world, but the mechanistic basis underlying the increase is often unclear. One possibility, especially in summer-dry climates, is that N fertilization increases the efficiency with which a finite water supply is consumed to support photosynthesis. This increase is achieved by a reduction in the canopy-integrated concentration of internal CO₂ and thus discrimination against ¹³C. We used stable isotopes of carbon (¹³C) in tree rings to experimentally test the physiological impact of N fertilization on mature Douglas-fir (Pseudotsuga menziesii Franco var. glauca) stands across the geographic extent of the Intermountain West, USA. The concentration and the stable isotopes of N (¹⁵N) in tree rings were also used to assess the presence and activity of fertilizer N. We hypothesized that N fertilization would (i) increase ¹⁵N and N concentration of stemwood relative to non-fertilized stands and (ii) increase stemwood ¹³C as photosynthetic gas exchange responded to the additional N. This experiment included two rates of urea addition, 178 kg ha^–1 (low) and 357 kg ha^–1 (high), which were applied twice over a 6-year interval bracketed by the 18 years of wood production measured in this study. Foliar N concentrations measured the year after each fertilization treatment suggest that the fertilizer N had been assimilated by the trees (P < 0.001). The N fertilization significantly enriched stemwood ¹⁵N by 1.3 at the low fertilization rate and by 2.4 at the high rate (P < 0.001) despite variation in soil N between sites. However, we found no significant effect of the N fertilizer on ¹³C of the annual rings (P = 0.76). These data lead us to suggest that alternative mechanisms underlie the growth response to fertilizer, i.e., increase in canopy area and shifts in biomass allocation.

The effects of cleared larch canopy and nitrogen supply on gas exchange and leaf traits in deciduous broad-leaved tree seedlings

Kitaoka, S., Watanabe, Y., Koike, T. — Thu, 12 Nov 2009 00:17:46 PST

To understand the leaf-level responses of successional tree species to forest gap formation and nitrogen deposition, we performed canopy clearing and nitrogen-amendment treatments in larch plantations and investigated the changes in the light-use characteristics and the leaf structure of the invading deciduous broad-leaved tree seedlings. We hypothesized that the responses of the tree seedlings to clearing and nitrogen input would reflect specific traits in the shoot development that would be related to the species-specific successional characteristics. The gap phase species Magnolia hyporeuca Siebold et Zucc. and the mid-late successional tree species Quercus mongolica Fischer ex Ledeb. var. crispula (Blume) Ohashi., which grow in or near the forest gaps, had higher light-saturated photosynthetic rates (Psat), enhanced mesophyll surface area (Smes) and increased leaf mass per area (LMA) under both the clearing treatment and the clearing with nitrogen-amendment treatment. These two species therefore increased their Psat via an increase in Smes and LMA. The LMA values of the late successional tree species Prunus ssiori F. Schmidt and Carpinus cordata Blume, which grow in the forest understory, were enhanced by the clearing treatment. However, they displayed lesser responses to the clearing treatment under which there were no marked increases in Psat or Smes values in the second year. These results indicate distinct and varied responses to disturbance regimes among the four seral tree seedlings. The Psat value largely increased in line with the increase in Smes value during the second year in M. hyporeuca and Q. mongolica. The nitrogen supply accelerated the change in LMA and increased the Smes value in the leaves of Q. mongolica.

Elevated CO2 increases root exudation from loblolly pine (Pinus taeda) seedlings as an N-mediated response

Phillips, R. P., Bernhardt, E. S., Schlesinger, W. H. — Thu, 12 Nov 2009 00:17:46 PST

The degree to which forest ecosystems provide a long-term sink for increasing atmospheric CO₂ depends upon the capacity of trees to increase the availability of growth-limiting resources. It has been widely speculated that trees exposed to CO₂ enrichment may increase the release of root exudates to soil as a mechanism to stimulate microbes to enhance nutrient availability. As a first test to examine how the atmospheric CO₂ and nitrogen availability affect the rates of root exudation, we performed two experiments in which the exudates were collected from loblolly pine (Pinus taeda L.) seedlings that were grown in controlled growth chambers under low and high CO₂ and at low and high rates of N supply. Despite the differences in experimental design between the two studies, plants grown at high CO₂ were larger, and thus whole plant exudation rates were higher under elevated CO₂ (P = 0.019), but the magnitude of this response depended on the N level in both studies. Seedlings increased mass-specific exudation rates in response to elevated CO₂ in both experiments, but only at low N supply. Moreover, N supply had a greater impact on the exudation rates than did CO₂, with mass-specific exudation rates significantly greater (98% and 69% in Experiments 1 and 2, respectively) in the seedlings grown at low N supply relative to high N supply. These results provide preliminary evidence that loblolly pines alter exudation rates in response to both CO₂ concentration and N supply, and support the hypothesis that increased C allocation to root exudates may be a mechanism by which trees could delay progressive N limitation in forested ecosystems.

Plastic responses of Abies pinsapo xylogenesis to drought and competition

Linares, J. C., Camarero, J. J., Carreira, J. A. — Thu, 12 Nov 2009 00:17:46 PST

Radial growth and xylogenesis were studied to investigate the influence of climate variability and intraspecific competition on secondary growth in Abies pinsapo Boiss., a relic Mediterranean fir. We monitored the responses to three thinning treatments (unthinned control –C–, 30% –T30– and 60% –T60– of basal area removed) to test the hypothesis that they may improve the adaptation capacity of tree growth to climatic stress. We also assessed whether xylogenesis was differentially affected by tree-to-tree competition. Secondary growth was assessed using manual band dendrometers from 2005 to 2007. In 2006, xylogenesis (phases of tracheid formation) was also investigated by taking microcores and performing histological analyses. Seasonal dynamics of radial increment were modeled using Gompertz functions and correlations with microclimate and radiation were performed. Histological analyses revealed it as fundamental to calibrate the dendrometer estimates of radial increment and to establish the actual onset and end dates of tracheid production. The lower radial-increment rates and number of produced tracheids were observed in the trees subjected to high competition in the unthinned plots. The growing season differed among the plots, and its duration ranged from an average of 78 days in unthinned plots to 115 days in thinned ones (T60). Variations in the beginning of the growing season (13 April to 22 May) and earlywood–latewood transition (early August) were mainly determined by the temperature pattern, while the onset and the end of the growing season were related to both annual precipitation and tree-to-tree competition. The tracheid-formation phases of radial enlargement and cell-wall thickening showed similar patterns in the trees from thinned and unthinned plots subjected to low and high competition, respectively, but the mean number of tracheids in each phase was always higher in the trees from the thinned plots. The reduction of competition through thinning induced a longer growing season and enhanced the radial growth in A. pinsapo.

Xylem anatomy correlates with gas exchange, water-use efficiency and growth performance under contrasting water regimes: evidence from Populus deltoides x Populus nigra hybrids

Fichot, R., Laurans, F., Monclus, R., Moreau, A., Pilate, G., Brignolas, F. — Thu, 12 Nov 2009 00:17:46 PST

Six Populus deltoides Bartr. ex Marsh. x P. nigra L. genotypes were selected to investigate whether stem xylem anatomy correlated with gas exchange rates, water-use efficiency (WUE) and growth performance. Clonal copies of the genotypes were grown in a two-plot common garden test under contrasting water regimes, with one plot maintained irrigated and the other one subjected to moderate summer water deficit. The six genotypes displayed a large range of xylem anatomy, mean vessel and fibre diameter varying from about 40 to 60 µm and from 7.5 to 10.5 µm, respectively. Decreased water availability resulted in a reduced cell size and an important rise in vessel density, but the extent of xylem plasticity was both genotype and trait dependent. Vessel diameter and theoretical xylem-specific hydraulic conductivity correlated positively with stomatal conductance, carbon isotope discrimination and growth performance-related traits and negatively with intrinsic WUE, especially under water deficit conditions. Vessel diameter and vessel density measured under water deficit conditions correlated with the relative losses in biomass production in response to water deprivation; this resulted from the fact that a more plastic xylem structure was generally accompanied by a larger loss in biomass production.

Water deficit affects mesophyll limitation of leaves more strongly in sun than in shade in two contrasting Picea asperata populations

Duan, B., Li, Y., Zhang, X., Korpelainen, H., Li, C. — Thu, 12 Nov 2009 00:17:46 PST

The aim of this study was to examine the response of internal conductance to CO₂ (g_i) to soil water deficit and contrasting light conditions, and their consequences on photosynthetic physiology in two Picea asperata Mast. populations originating from wet and dry climate regions of China. Four-year-old trees were subjected to two light treatments (30% and 100% of full sunlight) and two watering regimes (well watered, drought) for 2 years. In both tested populations, drought significantly decreased g_i and the net photosynthesis rate (A) and increased carbon isotope composition (¹³C) values in both light treatments, in particular in the sun. Moreover, drought resulted in a significantly higher relative limitation due to stomatal conductance (L_s) in both light treatments and higher relative limitation due to internal conductance (L_i) and abscisic acid (ABA) in the sun plants. The results also showed that L_i (0.26–0.47) was always greater than L_s (0.12–0.28). On the other hand, drought significantly decreased the ratio of chloroplastic to internal CO₂ concentration (C_c/C_i), photosynthetic nitrogen utilization efficiency (PNUE) and total biomass in the sun plants of the wet climate population, whereas there were no significant changes in these parameters in the dry climate population. Our results also showed that the dry climate population possessed higher ¹³C values with higher ratio of internal conductance to stomatal conductance (g_i/g_s), suggesting that increasing the g_i/g_s ratio enhances water-use efficiency (WUE) in plants evolved in arid environments. Thus, we propose that the use of the g_i/g_s parameter to screen P. asperata plants with higher water deficit tolerance is certainly worthy of consideration. Furthermore, g_i is an important variable, which reflects the population differences in PNUE, and it should thus be included in plant physiological investigations related to leaf economics.

Storage and transpiration have negligible effects on {delta}13C of stem CO2 efflux in large conifer trees

Thu, 12 Nov 2009 00:17:46 PST

Stem respiration rates are often quantified by measuring the CO₂ efflux from stems into chambers. It has been suggested that these measurements underestimate respiration because some of the respired CO₂ can be either retained or transported upwards in the transpiration stream. If the stem CO₂ efflux does not represent all respired CO₂, then the interpretation of its isotopic signal may be compromised as well. The C-isotope composition of the respired CO₂ and the measured efflux could differ due to (i) the release of CO₂ produced elsewhere into the stem and transported upwards in xylem water (soil CO₂ or root respired CO₂); (ii) the retention or release of CO₂ storage pools within the tree stem and (iii) the removal of CO₂ by the transpiration stream. We investigated the effects of these processes in large conifer trees using two manipulative experiments: a labelling experiment and a crown removal experiment. The labelling experiment used an extreme enrichment of dissolved CO₂ in soil water to assess the C uptake by the roots. In this experiment, we found no contamination of the stem CO₂ pool despite clear evidence that the water itself had been taken up. The crown removal experiment tested for vertical CO₂ flux in xylem water by eliminating transpiration. Here, we found no change in the ¹³C of stem CO₂ efflux (_EA; P > 0.05). We concluded that for these large conifers, sap-flow influenced neither ¹³C of stem efflux nor that of the stem CO₂ pool. By parameterizing Henry’s Law for conditions inside the stem, we estimated the transport flux to represent 1–3% of the stem CO₂ efflux to the atmosphere. Finally, assuming a 2 difference between ¹³C of root and stem respiration, we estimated that potential contamination of _EA by root respired CO₂ would be < 0.1. Thus, neither the release of soil or root CO₂, nor storage in the stem, nor vertical transport of CO₂ in the xylem sap had any detectable influence on ¹³C of the CO₂ measured in stem efflux.

Water deficit-induced changes in mesocarp cellular processes and the relationship between mesocarp and endocarp during olive fruit development

Gucci, R., Lodolini, E. M., Rapoport, H. F. — Thu, 12 Nov 2009 00:17:46 PST

A field experiment was conducted during two consecutive growing seasons to determine and quantify the growth response of the olive (Olea europaea L. cv. Leccino) fruit and of its component tissues to tree water status. Pre-dawn leaf water potential (_w) and fruit volume were measured at about weekly intervals, and fresh weight (FW) and dry weight (DW) of the fruit tissues at 15, 20 and 21 weeks after full bloom (AFB). Fruit anatomical sections were prepared at 8, 15 and 21 weeks AFB for area determinations and cell counts. Fruit volume of the well-watered trees (average _w = –0.97 MPa) increased rapidly and reached the greatest final size, that from the most stressed (average _w = –2.81 MPa) grew most slowly and were smallest. In general, equatorial transverse areas of the mesocarp increased with increasing _w, and this response was more evident at 21 than at 15 weeks AFB. By 21 weeks AFB, the mesocarp of the well-watered trees reached values more than three times higher than those measured at 8 weeks AFB. The endocarp FW and DW did not increase between 15 and 21 weeks AFB. Within each sampling date the endocarp area, FW and DW responded weakly to _w. The mesocarp-to-endocarp ratio (FW and DW) increased from 15 to 21 weeks AFB regardless of water status, mainly due to the mesocarp growth. In both years at 20 and 21 weeks AFB, low values of the mesocarp-to-endocarp ratio were found with _w below –2.5 MPa. Within the mesocarp, cell size was more responsive to water deficit than to cell number. At 8 weeks AFB, the number of cells in the mesocarp was unaffected by tree water deficit, whereas cell size decreased, although slightly, in fruits sampled from trees in which _w was < –3.0 MPa. At 21 weeks AFB, cell size showed a linear decrease with increasing level of water deficit, whereas the number of cells at 21 weeks AFB decreased as the _w decreased below –2.5 MPa and seemed unaffected above that range. Overall, the results clarify the complexity of the water-induced response of mesocarp and endocarp growth and cellular processes of olive fruits.

Pinus pinaster seedlings and their fungal symbionts show high plasticity in phosphorus acquisition in acidic soils

Ali, M.A., Louche, J., Legname, E., Duchemin, M., Plassard, C. — Thu, 12 Nov 2009 00:17:46 PST

Young seedlings of maritime pine (Pinus pinaster Soland in Aït.) were grown in rhizoboxes using intact spodosol soil samples from the southwest of France, in Landes of Gascogne, presenting a large variation of phosphorus (P) availability. Soils were collected from a 93-year-old unfertilized stand and a 13-year-old P. pinaster stand with regular annual fertilization of either only P or P and nitrogen (N). After 6 months of culture in controlled conditions, different morphotypes of ectomycorrhiza (ECM) were used for the measurements of acid phosphatase activity and molecular identification of fungal species using amplification of the ITS region. Total biomass, N and P contents were measured in roots and shoots of plants. Bicarbonate- and NaOH-available inorganic P (Pi), organic P (Po) and ergosterol concentrations were measured in bulk and rhizosphere soil. The results showed that bulk soil from the 93-year-old forest stand presented the highest Po levels, but relatively higher bicarbonate-extractable Pi levels compared to 13-year-old unfertilized stand. Fertilizers significantly increased the concentrations of inorganic P fractions in bulk soil. Ergosterol contents in rhizosphere soil were increased by fertilizer application. The dominant fungal species was Rhizopogon luteolus forming 66.6% of analysed ECM tips. Acid phosphatase activity was highly variable and varied inversely with bicarbonate-extractable Pi levels in the rhizosphere soil. Total P or total N in plants was linearly correlated with total plant biomass, but the slope was steep only between total P and biomass in fertilized soil samples. In spite of high phosphatase activity in ECM tips, P availability remained a limiting nutrient in soil samples from unfertilized stands. Nevertheless young P. pinaster seedlings showed a high plasticity for biomass production at low P availability in soils.

Immunohistochemical localization of enzymes that catalyze the long sequential pathways of lignin biosynthesis during differentiation of secondary xylem tissues of hybrid aspen (Populus sieboldii x Populus grandidentata)

Thu, 12 Nov 2009 00:17:46 PST

We have investigated the spatial localization of enzymes that catalyze the sequential pathways of lignin biosynthesis in developing secondary xylem tissues of hybrid aspen (Populus sieboldii Miq. x Populus grandidentata Michx.) using immunohistochemical techniques. The enzymes phenylalanine ammonia-lyase, caffeic acid 3-O-methyltransferase and 4-coumarate:CoA ligase in the common phenylpropanoid pathway, cinnamyl-alcohol dehydrogenase (CAD) and peroxidase in the specific lignin pathway, 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (DAHPS) in the shikimate pathway and glutamine synthetase (GS) in the nitrogen reassimilation system were abundantly localized in the 6th to 9th wood fibers away from cambium; these wood fibers are likely undergoing the most intense lignification. Only weak immunolabeling of enzymes involved in the general phenylpropanoid and specific lignin pathways was detected in the cells near the cambium; lignification of these cells has likely been initiated after primary cell wall formation. In contrast, distinct localization of DAHPS and GS was observed around the cambium, which may be involved not only in lignin biosynthesis, but also in amino acid and protein synthesis, which are essential for cell survival. Our observations suggest that co-localization of enzymes related to the sequential shikimate, general phenylpropanoid and specific lignin branch pathways and to the nitrogen recycling system is associated with cell wall lignification of wood fibers during secondary xylem development.

Cloning and expression analysis of 14 lipid transfer protein genes from Tamarix hispida responding to different abiotic stresses

Wang, C., Yang, C., Gao, C., Wang, Y. — Thu, 12 Nov 2009 00:17:46 PST

Plant lipid transfer proteins (LTPs) are ubiquitous lipid-binding proteins that are involved in various stress responses. In this study, we cloned 14 unique LTP genes (ThLTP 1–14) from Tamarix hispida Willd. (Tamaricaceae) to investigate their roles under various abiotic stress conditions. The expression profiles of the 14 ThLTPs in response to NaCl, polyethylene glycol (PEG), NaHCO₃, CdCl₂ and abscisic acid (ABA) exposure in root, stem and leaf tissues were investigated using real-time RT-PCR. The results showed that all 14 ThLTPs were expressed in root, stem and leaf tissues under normal growth conditions. However, under normal growth conditions, ThLTP abundance varied in each organ, with expression differences of 9000-fold in leaves, 540-fold in stems and 3700-fold in roots. These results indicated that activity and/or physiological importance of these ThLTPs are quite different. Differential expression of the 14 ThLTPs was observed (> 2-fold) for NaCl, PEG, NaHCO₃ and CdCl₂ in at least one tissue indicating that they were all involved in abiotic stress responses. All ThLTP genes were highly induced (> 2-fold) under ABA treatment in roots, stems and/or leaves, and particularly in roots, suggesting that ABA-dependent signaling pathways regulated ThLTPs. We hypothesize that ThLTP expression constitutes an adaptive response to abiotic stresses in T. hispida and plays an important role in abiotic stress tolerance.

Ecophysiological evaluation of the potential invasiveness of Rhus typhina in its non-native habitats

Zhang, Z., Jiang, C., Zhang, J., Zhang, H., Shi, L. — Thu, 22 Oct 2009 03:24:02 PDT

Rhus typhina L. (staghorn sumac) is a clonal woody species that is considered potentially invasive in its non-native habitats. It is slow growing as seedlings, but grows fast once established. Its growth in the early stages is limited by many abiotic factors, including light intensity. To evaluate its potential of becoming invasive in areas it has been introduced into, we conducted a field experiment to investigate the effects of light intensity on the physiology and growth of R. typhina. Two-month-old R. typhina seedlings were examined under five light levels, that is, 100% full sunlight (unlimited light), moderate stress (50% or 25% of full sunlight) and severe stress (10% or 5% of full sunlight), for 60 days in Hunshandak Sandland, China. Net photosynthetic rate (P_N) was reduced significantly under severe light stress, but P_N of the moderately stressed seedlings was unaffected. Light stress also led to a reduction in saturated light intensity of the moderately stressed seedlings by 20% and of the severely stressed seedlings by 40%, although the light saturation points were as high as 800 and 600 µmol m^–2 s^–1 for the moderately and severely stressed seedlings, respectively. Under severe light stress, the maximum quantum yield of Photosystem II (F_v/F_m) decreased significantly, but the minimal fluorescence yield (F₀) increased compared to that of the control plants. The number of newly produced leaves and the stem height, however, decreased as the light intensity became lower. Root length and leaf area decreased, whereas specific leaf area significantly increased as light became increasingly lower. Biomass production was significantly reduced by light stress, but the allocation pattern was unaffected. Our results demonstrated that R. typhina seedlings can survive low light and grow well in other light conditions. The physiology and growth of R. typhina will likely enable it to acclimate to varying light conditions in Hunshandak Sandland, where R. typhina has been widely cultivated for sand stabilization and other purposes. Because of its ability to tolerate low light and to compete aggressively for light resource once established, that is, becoming invasive, we urge caution when it comes to introducing R. typhina into its non-native habitats, despite its many ecological benefits.

Age class, longevity and growth rate relationships: protracted growth increases in old trees in the eastern United States

Johnson, S. E., Abrams, M. D. — Thu, 22 Oct 2009 03:24:02 PDT

This study uses data from the International Tree-Ring Data Bank website and tree cores collected in the field to explore growth rate (basal area increment, BAI) relationships across age classes (from young to old) for eight tree species in the eastern US. These species represent a variety of ecological traits and include those in the genera Populus, Quercus, Pinus, Tsuga and Nyssa. We found that most trees in all age classes and species exhibit an increasing BAI throughout their lives. This is particularly unusual for trees in the older age classes that we expected to have declining growth in the later years, as predicted by physiological growth models. There exists an inverse relationship between growth rate and increasing age class. The oldest trees within each species have consistently slow growth throughout their lives, implying an inverse relationship between growth rate and longevity. Younger trees (< 60 years of age) within each species are consistently growing faster than the older trees when they are of the same age resulting from a higher proportion of fast-growing trees in these young age classes. Slow, but increasing, BAI in the oldest trees in recent decades is a continuation of their growth pattern established in previous centuries. The fact that they have not shown a decreasing growth rate in their old age contradicts physiological growth models and may be related to the stimulatory effects of global change phenomenon (climate and land-use history).

Productivity, water-use efficiency and tolerance to moderate water deficit correlate in 33 poplar genotypes from a Populus deltoides x Populus trichocarpa F1 progeny

Thu, 22 Oct 2009 03:24:02 PDT

Genotypic variability for productivity, water-use efficiency and leaf traits in 33 genotypes selected from an F₁ progeny of Populus deltoides Bartr. ex Marsh x Populus trichocarpa L. was explored under optimal and moderate water-deficit conditions. Saplings of the 33 genotypes were grown in a two-plot open field at INRA Orléans (France) and coppiced every year. A moderate water deficit was induced during two successive years on one plot by withholding irrigation, while the second one remained irrigated (control). Stem biomass and leaf structure (e.g., specific leaf area and leaf area) were measured in 2004 and 2005 and functional leaf traits (e.g., carbon isotope discrimination, ) were measured only in 2004. Tolerance to water deficit was estimated at genotype level as the ability to limit losses in biomass production in water deficit versus control trees. Stem biomass, leaf structure and displayed a significant genotypic variability whatever the irrigation regime. For all traits, genotype ranks remained stable across years for similar irrigation conditions. Carbon isotope discrimination scaled negatively with productivity and leaf nitrogen content in controls. The most productive genotypes were the least tolerant to moderate water deficit. No relationship was evidenced between and the level of tolerance to water deficit. The relationships between traits evidenced in this collection of P. deltoides x P. trichocarpa F₁ genotypes contrast with the ones that were previously detected in a collection of P. deltoides x Populus nigra L. cultivars tested in the same field trial.

Low moisture availability inhibits the enhancing effect of increased soil temperature on net photosynthesis of white birch (Betula papyrifera) seedlings grown under ambient and elevated carbon dioxide concentrations

Ambebe, T. F., Dang, Q.-L. — Thu, 22 Oct 2009 03:24:02 PDT

White birch (Betula papyrifera Marsh.) seedlings were grown under two carbon dioxide concentrations (ambient: 360 µmol mol^–1 and elevated: 720 µmol mol^–1), three soil temperatures (5, 15 and 25 °C initially, increased to 7, 17 and 27 °C, respectively, 1 month later) and three moisture regimes (low: 30–40%; intermediate: 45–55% and high: 60–70% field water capacity) in greenhouses. In situ gas exchange and chlorophyll fluorescence were measured after 2 months of treatments. Net photosynthetic rate (A_n) of seedlings grown under the intermediate and high moisture regimes increased from low to intermediate T_soil and then decreased to high T_soil. There were no significant differences between the low and high T_soil, with the exception that A_n was significantly higher under high than low T_soil at the high moisture regime. No significant T_soil effect on A_n was observed at the low moisture regime. The intermediate T_soil increased stomatal conductance (g_s) only at intermediate and high but not at low moisture regime, whereas there were no significant differences between the low and high T_soil treatments. Furthermore, the difference in g_s between the intermediate and high T_soil at high moisture regime was not statistically significant. The low moisture regime significantly reduced the internal to ambient CO₂ concentration ratio at all T_soil. There were no significant individual or interactive effects of treatment on maximum carboxylation rate of Rubisco, light-saturated electron transport rate, triose phosphate utilization or potential photochemical efficiency of photosystem II. The results of this study suggest that soil moisture condition should be taken into account when predicting the responses of white birch to soil warming.

Within-canopy and ozone fumigation effects on {delta}13C and {Delta}18O in adult beech (Fagus sylvatica) trees: relation to meteorological and gas exchange parameters

Thu, 22 Oct 2009 03:24:02 PDT

In this study, the effects of different light intensities either in direct sunlight or in the shade crown of adult beech (Fagus sylvatica L.) trees on ¹³C and ¹⁸O were determined under ambient (1 x O₃) and twice-ambient (2 x O₃) atmospheric ozone concentrations during two consecutive years (2003 and 2004). We analysed the isotopic composition in leaf bulk, leaf cellulose, phloem and xylem material and related the results to (a) meteorological data (air temperature, T and relative humidity, RH), (b) leaf gas exchange measurements (stomatal conductance, g_s; transpiration rate, E; and maximum photosynthetic activity, A_max) and (c) the outcome of a steady-state evaporative enrichment model. ¹³C was significantly lower in the shade than in the sun crown in all plant materials, whilst ¹⁸O was increased significantly in the shade than in the sun crown in bulk material and cellulose. Elevated ozone had no effect on ¹³C, although ¹⁸O was influenced by ozone to varied degrees during single months. We observed significant seasonal changes for both parameters, especially in 2004, and also significant differences between the study years. Relating the findings to meteorological data and gas exchange parameters, we conclude that the differences in ¹⁸O between the sun and the shade crown were predominantly caused by the Péclet effect. This assumption was supported by the modelled ¹⁸O values for leaf cellulose. It was demonstrated that independent of RH, light-dependent reduction of stomatal conductance (and thus transpiration) and of A_max can drive the pattern of ¹⁸O increase with the concomitant decrease of ¹³C in the shade crown. The effect of doubling ozone levels on time-integrated stomatal conductance and transpiration as indicated by the combined analysis of ¹⁸O and ¹³C was much lower than the influence caused by the light exposure.

Leaf and canopy conductance in aspen and aspen-birch forests under free-air enrichment of carbon dioxide and ozone

Uddling, J., Teclaw, R. M., Pregitzer, K. S., Ellsworth, D. S. — Thu, 22 Oct 2009 03:24:02 PDT

Increasing concentrations of atmospheric carbon dioxide (CO₂) and tropospheric ozone (O₃) have the potential to affect tree physiology and structure, and hence forest feedbacks on climate. Here, we investigated how elevated concentrations of CO₂ (+45%) and O₃ (+35%), alone and in combination, affected conductance for mass transfer at the leaf and canopy levels in pure aspen (Populus tremuloides Michx.) and in mixed aspen and birch (Betula papyrifera Marsh.) forests in the free-air CO₂–O₃ enrichment experiment near Rhinelander, Wisconsin (Aspen FACE). The study was conducted during two growing seasons, when steady-state leaf area index (L) had been reached after > 6 years of exposure to CO₂- and O₃-enrichment treatments. Canopy conductance (g_c) was estimated from stand sap flux, while leaf-level conductance of sun leaves in the upper canopy was derived by three different and independent methods: sap flux and L in combination with vertical canopy modelling, leaf ¹³C discrimination methodology in combination with photosynthesis modelling and leaf-level gas exchange. Regardless of the method used, the mean values of leaf-level conductance were higher in trees growing under elevated CO₂ and/or O₃ than in trees growing in control plots, causing a CO₂ x O₃ interaction that was statistically significant (P ≤ 0.10) for sap flux- and (for birch) ¹³C-derived leaf conductance. Canopy conductance was significantly increased by elevated CO₂ but not significantly affected by elevated O₃. Investigation of a short-term gap in CO₂ enrichment demonstrated a +10% effect of transient exposure of elevated CO₂-grown trees to ambient CO₂ on g_c. All treatment effects were similar in pure aspen and mixed aspen-birch communities. These results demonstrate that short-term primary stomatal closure responses to elevated CO₂ and O₃ were completely offset by long-term cumulative effects of these trace gases on tree and stand structure in determining canopy- and leaf-level conductance in pure aspen and mixed aspen-birch forests. Our results, together with the findings from other long-term FACE experiments with trees, suggest that model assumptions of large reductions in stomatal conductance under rising atmospheric CO₂ are very uncertain for forests.

Seasonal and long-term effects of CO2 and O3 on water loss in ponderosa pine and their interaction with climate and soil moisture

Thu, 22 Oct 2009 03:24:02 PDT

Evapotranspiration (ET) is driven by evaporative demand, available solar energy and soil moisture (SM) as well as by plant physiological activity which may be substantially affected by elevated CO₂ and O₃. A multi-year study was conducted in outdoor sunlit-controlled environment mesocosm containing ponderosa pine seedlings growing in a reconstructed soil–litter system. The study used a 2 x 2 factorial design with two concentrations of CO₂ (ambient and elevated), two levels of O₃ (low and high) and three replicates of each treatment. The objective of this study was to assess the effects of chronic exposure to elevated CO₂ and O₃, alone and in combination, on daily ET. This study evaluated three hypotheses: (i) because elevated CO₂ stimulates stomatal closure, O₃ effects on ET will be less under elevated CO₂ than under ambient CO₂; (ii) elevated CO₂ will ameliorate the long-term effects of O₃ on ET; and (iii) because conductance (g) decreases with decreasing SM, the impacts of elevated CO₂ and O₃, alone and in combination, on water loss via g will be greater in early summer when SM is not limiting than to other times of the year. A mixed-model covariance analysis was used to adjust the daily ET for seasonality and the effects of SM and photosynthetically active radiation when testing for the effects of CO₂ and O₃ on ET via the vapor pressure deficit gradient. The empirical results indicated that the interactive stresses of elevated CO₂ and O₃ resulted in a lesser reduction in ET via reduced canopy conductance than the sum of the individual effects of each gas. CO₂-induced reductions in ET were more pronounced when trees were physiologically most active. O₃-induced reductions in ET under ambient CO₂ were likely transpirational changes via reduced conductance because needle area and root biomass were not affected by exposures to elevated O₃ in this study.

Hydraulic properties of naturally regenerated beech saplings respond to canopy opening

Thu, 22 Oct 2009 03:24:03 PDT

Enhanced sapling growth in advance regeneration requires gaps in the canopy, but is often delayed after canopy opening, because acclimation of saplings to the new environment is gradual and may last for several years. Canopy opening is expected to result in an increased transpiration because of a larger climatic demand and a higher stomatal conductance linked to the higher rates of photosynthesis. Therefore, we focused on the changes in water relations and the hydraulic properties of beech (Fagus sylvatica L.) saplings during 2 years after canopy opening. We tested the hypothesis that an increase in leaf-specific hydraulic conductance and a decrease in vulnerability to cavitation occur to sustain an enhanced transpiration. Hydraulic conductance of defoliated shoots, vulnerability to cavitation, size and density of xylem vessels as well as stomatal conductance were recorded on saplings growing in shade (S saplings) or in gaps created by opening the canopy (shade-to-light, SL saplings). Hydraulic conductance per unit cross-sectional area (K_AS) did not differ in the shoots of S and SL saplings. But a higher ratio stem cross-sectional area/leaf area resulted in a higher leaf-specific hydraulic conductance of the shoots (K_AL) of SL saplings. Contrary to expectations, vulnerability to cavitation increased transitorily in stems during the first year after canopy opening and no difference was observed between the two treatments in light-saturated stomatal conductance. During the second year, vulnerability to cavitation was similar in the S and SL saplings and light-saturated stomatal conductance increased in SL saplings. These results demonstrate a release of the hydraulic constraints after canopy opening with an adjustment of the ratio stem cross-sectional area/leaf area. But the larger vulnerability to cavitation during the first year could limit stomatal opening and therefore the ability of beech saplings to use the available light for photosynthesis and could therefore partly explain why the growth increase was delayed to the second growing season after canopy opening.

Plasticity in the Huber value contributes to homeostasis in leaf water relations of a mallee Eucalypt with variation to groundwater depth

Carter, J. L., White, D. A. — Thu, 22 Oct 2009 03:24:03 PDT

Information on how vegetation adapts to differences in water supply is critical for predicting vegetation survival, growth and water use, which, in turn, has important impacts on site hydrology. Many field studies assess adaptation to water stress by comparing between disparate sites, which makes it difficult to distinguish between physiological or morphological changes and long-term genetic adaptation. When planting trees into new environments, the phenotypic adaptations of a species to water stress will be of primary interest. This study examined the response to water availability of Eucalyptus kochii ssp. borealis (C. Gardner) D. Nicolle, commonly integrated with agriculture in south-western Australia for environmental and economic benefits. By choosing a site where the groundwater depth varied but where climate and soil type were the same, we were able to isolate tree response to water supply. Tree growth, leaf area and stand water use were much larger for trees over shallow groundwater than for trees over a deep water table below a silcrete hardpan. However, water use on a leaf area basis was similar in trees over deep and shallow groundwater, as were the minimum leaf water potential observed over different seasons and the turgor loss point. We conclude that homeostasis in leaf water use and water relations was maintained through a combination of stomatal control and adjustment of sapwood-to-leaf area ratios (Huber value). Differences in the Huber value with groundwater depth were associated with different sapwood-specific conductivity and water use on a sapwood area basis. Knowledge of the coordination between water supply, leaf area, sapwood area and leaf transpiration rate for different species will be important when predicting stand water use.

Shrinkage processes in standard-size Norway spruce wood specimens with different vulnerability to cavitation

Rosner, S., Karlsson, B., Konnerth, J., Hansmann, C. — Thu, 22 Oct 2009 03:24:03 PDT

The aim of this study was to observe the radial shrinkage of Norway spruce [Picea abies (L. Karst.)] trunkwood specimens with different hydraulic vulnerability to cavitation from the fully saturated state until the overall shrinkage reaches a stable value, and to relate wood shrinkage and recovery from shrinkage to cavitations of the water column inside the tracheids. Radial shrinkage processes in standard-size sapwood specimens (6 mm x 6 mm x 100 mm; radial, tangential and longitudinal) obtained at different positions within the trunk, representing different ages of the cambium, were compared. Cavitation events were assessed by acoustic emission (AE) testing, hydraulic vulnerability by the AE feature analysis and shrinkage was calculated from the changes in contact pressure between the 150 kHz AE transducer and the wood specimen. Two shrinkage processes were observed in both juvenile (annual rings 1 and 2) and mature wood (annual rings 17–19), the first one termed tension shrinkage and the second one cell wall shrinkage process, which started when most of the tracheids reached relative water contents below fiber saturation. Maximum tension shrinkage coincided with high-energy AEs, and the periods of shrinkage recovery could be traced to tension release due to cavitation. Juvenile wood, which was less sensitive to cavitation, had lower earlywood tracheid diameters and was less prone to deformation due to tensile strain than mature wood, showed a lower cell wall shrinkage, and thus total shrinkage. Earlywood lumen diameters and maximum tension shrinkage were strongly positively related to each other, meaning that bigger tracheids are more prone to deformation at the same water tension than the smaller tracheids.

Tracing of recently assimilated carbon in respiration at high temporal resolution in the field with a tuneable diode laser absorption spectrometer after in situ 13CO2 pulse labelling of 20-year-old beech trees

Thu, 22 Oct 2009 03:24:03 PDT

The study of the fate of assimilated carbon in respiratory fluxes in the field is needed to resolve the residence and transfer times of carbon in the atmosphere–plant–soil system in forest ecosystems, but it requires high frequency measurements of the isotopic composition of evolved CO₂. We developed a closed transparent chamber to label the whole crown of a tree and a labelling system capable of delivering a 3-h pulse of 99% ¹³CO₂ in the field. The isotopic compositions of trunk and soil CO₂ effluxes were recorded continuously on two labelled and one control trees by a tuneable diode laser absorption spectrometer during a 2-month chase period following the late summer labelling. The lag times for trunk CO₂ effluxes are consistent with a phloem sap velocity of about 1 m h^–1. The isotopic composition (¹³C) of CO₂ efflux from the trunk was maximal 2–3 days after labelling and declined thereafter following two exponential decays with a half-life of 2–8 days for the first and a half-life of 15–16 days for the second. The isotopic composition of the soil CO₂ efflux was maximal 3–4 days after labelling and the decline was also well fitted with a sum of two exponential functions with a half-life of 3–5 days for the first exponential and a half-life of 16–18 days for the second. The amount of label recovered in CO₂ efflux was around 10–15% of the assimilated ¹³CO₂ for soil and 5–13% for trunks. As labelling occurred late in the growing season, substantial allocation to storage is expected.

Interpretation of stem CO2 efflux measurements

Holtta, T., Kolari, P. — Thu, 22 Oct 2009 03:24:03 PDT

It is known that stem CO₂ efflux differs somewhat both temporally and spatially from actual stem respiration, but relations between these two are not fully understood. A physical model of CO₂ diffusion and advection by xylem sap flow is developed to interpret the CO₂ flux signal from the stem. Model predictions are compared against measured CO₂ efflux data from a field-grown 16-m Pinus sylvestris L. tree. The ratio of CO₂ efflux to CO₂ production is predicted to be much larger in the upper part of the tree than in the lower part as the xylem sap carries the respired CO₂ upwards. The model also predicts the temperature dependency of real respiration to be higher than that of the CO₂ efflux due to the slowness of diffusion. The relation between stem respiration and CO₂ efflux depends strongly on the sap flow rate, radial diffusion resistance and stem geometry and size. The model may be used to scale individual CO₂ efflux measurements to evaluate the respiration rate of whole trees and forests.

Anatomy and morphology in developing vegetative buds on detached Norway spruce branches in controlled conditions before bud burst

Sutinen, S., Partanen, J., Vihera-Aarnio, A., Hakkinen, R. — Thu, 22 Oct 2009 03:24:03 PDT

We studied the light and stereomicroscopic structure of developing vegetative buds from a 16-year-old Norway spruce [Picea abies (L.) Karst.] of southern Finnish origin in relation to temperature sum and to externally visible changes in the buds before and during bud burst in forcing conditions. Branches were collected on 17 January and transferred to the greenhouse where they were first subjected to preforcing conditions (darkness, +4 °C) for 7 days and then to the forcing conditions (day length 12 h, +20 °C). Buds were sampled 20 times between 17 January and 13 February. Air temperature was recorded hourly throughout the study period. The first microscopic change was a temporary increase in the size and number of lipid droplets before the onset of temperature sum (T ≥ +5 °C) accumulation. From the 4th to the 9th day under the forcing conditions, tracheids started to develop from the base up to the top of the bud. This was closely synchronized with an observed morphological change in the shape of needle tip from rounded to pointed ones. Development from the first visible change in the bud scales on the 12th forcing day to bud burst took 9 days when the temperature sum was 313 d.d. The temperature sums in our experiment overestimated the requirements of temperature sum for bud development phases measured in the field. Bud development could be divided into four structural phases. The first two phases, i.e., morphological changes in the primary needles, occurred without any externally visible changes in the buds. Thus, these phases have a potential for testing and improving the phenological models, which, up to now, have mainly been based on the bud burst observation by the naked eye.

Functional analysis of putative genes encoding the PIP2 water channel subfamily in Populus trichocarpa

Secchi, F., Maciver, B., Zeidel, M. L., Zwieniecki, M. A. — Thu, 22 Oct 2009 03:24:03 PDT

We located fully sequenced putative genes of the plasma membrane intrinsic proteins (PIPs) family in the Populus trichocarpa (Torr. Gray), genome. Of 23 gene candidates, we assigned eight genes to the PIP2 subfamily. All eight putative genes were expressed in vegetative tissues (roots, leaves, bark and wood), and all of them showed water channel activity after being expressed in Xenopus oocytes. Six of eight proteins were affected by mercury ions. No proteins were affected by the presence of nickel or tungsten ions, or by lowering the pH of bathing external solution from 7.4 to 6.5. The presence of copper ions caused seven of eight PIP2 proteins to increase their water transport capacity by as much as 50%. This systematic study of the PIP2 subfamily of proteins in P. trichocarpa provides a basic overview of their activity as water channels and will be a useful reference for future physiological studies of plant water relations that use P. trichocarpa as a model system.

Role of transitory carbon reserves during adjustment to climate variability and source-sink imbalances in oil palm (Elaeis guineensis)

Wed, 23 Sep 2009 05:35:47 PDT

Oil palm (Elaeis guineensis Jacq.) is a perennial, tropical, monocotyledonous plant characterized by simple architecture and low phenotypic plasticity, but marked by long development cycles of individual phytomers (a pair of one leaf and one inflorescence at its axil). Environmental effects on vegetative or reproductive sinks occur with various time lags depending on the process affected, causing source–sink imbalances. This study investigated how the two instantaneous sources of carbon assimilates, CO₂ assimilation and mobilization of transitory non-structural carbohydrate (NSC) reserves, may buffer such imbalances. An experiment was conducted in Indonesia during a 22-month period (from July 2006 to May 2008) at two contrasting locations (Kandista and Batu Mulia) using two treatments (control and complete fruit pruning treatment) in Kandista. Measurements included leaf gas exchange, dynamics of NSC reserves and dynamics of structural aboveground vegetative growth (SVG) and reproductive growth. Drought was estimated from a simulated fraction of transpirable soil water. The main sources of variation in source–sink relationships were (i) short-term reductions in light-saturated leaf CO₂ assimilation rate (A_max) during seasonal drought periods, particularly in Batu Mulia; (ii) rapid responses of SVG rate to drought; and (iii) marked lag periods between 16 and 29 months of environmental effects on the development of reproductive sinks. The resulting source–sink imbalances were buffered by fluctuations in NSC reserves in the stem, which mainly consisted of glucose and starch. Starch was the main buffer for sink variations, whereas glucose dynamics remained unexplained. Even under strong sink limitation, no negative feedback on A_max was observed. In conclusion, the different lag periods for environmental effects on assimilate sources and sinks in oil palm are mainly buffered by NSC accumulation in the stem, which can attain 50% (dw:dw) in stem tops. The resulting dynamics of growth and production are complex because several dozen phytomers of different phenological ages develop at any given time and interact with a common pool of reserves.

Wood CO2 efflux and foliar respiration for Eucalyptus in Hawaii and Brazil

Wed, 23 Sep 2009 05:35:47 PDT

We measured CO₂ efflux from wood for Eucalyptus in Hawaii for 7 years and compared these measurements with those on three- and four-and-a-half-year-old Eucalyptus in Brazil. In Hawaii, CO₂ efflux from wood per unit biomass declined ~ 10x from age two to age five, twice as much as the decline in tree growth. The CO₂ efflux from wood in Brazil was 8–10x lower than that for comparable Hawaii trees with similar growth rates. Growth and maintenance respiration coefficients calculated from Hawaii wood CO₂ efflux declined with tree age and size (the growth coefficient declined from 0.4 mol C efflux mol C^–1 wood growth at age one to 0.1 mol C efflux mol C^–1 wood growth at age six; the maintenance coefficient from 0.006 to 0.001 µmol C (mol C biomass)^–1 s^–1 at 20 °C over the same time period). These results suggest interference with CO₂ efflux through bark that decouples CO₂ efflux from respiration. We also compared the biomass fractions and wood CO₂ efflux for the aboveground woody parts for 3- and 7-year-old trees in Hawaii to estimate how focusing measurements near the ground might bias the stand-level estimates of wood CO₂ efflux. Three-year-old Eucalyptus in Hawaii had a higher proportion of branches < 0.5 cm in diameter and a lower proportion of stem biomass than did 7-year-old trees. Biomass-specific CO₂ efflux measured at 1.4 m extrapolated to the tree could bias tree level estimates by ~ 50%, assuming no refixation from bark photosynthesis. However, the bias did not differ for the two tree sizes. Foliar respiration was identical per unit nitrogen for comparable treatments in Brazil and Hawaii (4.2 µmol C mol N^–1 s^–1 at 20 °C).

Intra-annual cambial activity and carbon availability in stem of poplar

Wed, 23 Sep 2009 05:35:47 PDT

Cambial activity is influenced by many environmental and physiological factors and among them, carbon acts as a source of energy for the growing meristems. This work has focused on the intra-annual stem growth of poplar compared with the carbon available for xylogenesis processes in cambium and outer wood. The major stages of xylem production and differentiation in two poplar genotypes with different growth performances were considered. Monitoring of stem growth and leaf phenology combined with starch, nonstructural soluble sugars and water content in the stem was conducted from February to November 2006 in Populus x canadensis Moench ‘I-214’ and Populus deltoides Marsh. ‘Dvina’. Anatomical analyses of wood formation were performed by measuring the width of the zones with differentiating and mature xylem. At the end of the growing period, wood density was assessed by microdensity analyses. Xylem differentiation at the top of the tree started at the beginning of April for both genotypes and proceeded down the stem at about 0.5 m day^–1, occurring almost at the same time as leaf opening. The rate of growth and wood density was superior in Dvina, but this higher productivity could not be explained by differences in the number of cambial initials and the duration of xylogenesis. However, the most productive poplar genotype showed higher glucose, fructose and sucrose content in the outer wood. The nonstructural soluble sugars available in the cambial zone followed the intra-annual pattern of xylem formation, with a higher concentration when the growth rate was maximum. The accumulations of nonstructural soluble sugars at a certain time during stem growth corresponded with a higher carbon availability to the actively growing meristems in the stem.

Leaf and whole tree adaptations to mild salinity in field grown Populus euphratica

Zeng, F., Yan, H., Arndt, S. K. — Wed, 23 Sep 2009 05:35:47 PDT

Populus euphratica Oliv. is a highly salt tolerant tree species, and this study represents the first comprehensive investigation of salt tolerance mechanisms of mature trees of P. euphratica in the field. We measured NaCl concentration in xylem sap, NaCl accumulation in leaves, the effect of NaCl on leaf physiological parameters and osmotic adjustment and the allocation and distribution of NaCl between different plant organs on a whole plant level in trees exposed to mild saline groundwater (around 30 mM) in China. Populus euphratica showed three key mechanisms of salt tolerance. The primary mechanism had a strong control over Na⁺ and Cl^– uptake with effective exclusion mechanisms for Cl^– with up to 99% of the external NaCl being excluded from the xylem. Secondly, the trees allocated large proportions of NaCl into the leaves, which served as a salt elimination mechanism as the leaves are ultimately shed at the end of the growing season. Thirdly, the trees tolerated high foliar Na⁺ concentrations through a combination of osmotic adjustment using sucrose and probable sequestering of Na⁺ in the apoplast. Our results indicate that the control of Na⁺ and Cl^– uptake and the regulation of Na⁺ and Cl^– delivery to the shoot are key to salt tolerance of P. euphratica in the field with tolerance of high Na⁺ concentrations in leaves being a critical component.

Three-dimensional analysis of the anatomical growth response of European conifers to mechanical disturbance

Schneuwly, D. M., Stoffel, M., Dorren, L. K.A., Berger, F. — Wed, 23 Sep 2009 05:35:47 PDT

Studies on tree reaction after wounding were so far based on artificial wounding or chemical treatment. For the first time, type, spread and intensity of anatomical responses were analyzed and quantified in naturally disturbed Larix decidua Mill., Picea abies (L.) Karst. and Abies alba Mill. trees. The consequences of rockfall impacts on increment growth were assessed at the height of the wounds, as well as above and below the injuries. A total of 16 trees were selected on rockfall slopes, and growth responses following 54 wounding events were analyzed on 820 cross-sections. Anatomical analysis focused on the occurrence of tangential rows of traumatic resin ducts (TRD) and on the formation of reaction wood. Following mechanical disturbance, TRD production was observed in 100% of L. decidua and P. abies wounds. The radial extension of TRD was largest at wound height, and they occurred more commonly above, rather than below, the wounds. For all species, an intra-annual radial shift of TRD was observed with increasing axial distance from wounds. Reaction wood was formed in 87.5% of A. alba following wounding, but such cases occurred only in 7.7% of L. decidua. The results demonstrate that anatomical growth responses following natural mechanical disturbance differ significantly from the reactions induced by artificial stimuli or by decapitation. While the types of reactions remain comparable between the species, their intensity, spread and persistence disagree considerably. We also illustrate that the external appearance of wounds does not reflect an internal response intensity. This study reveals that disturbance induced under natural conditions triggers more intense and more widespread anatomical responses than that induced under artificial stimuli, and that experimental laboratory tests considerably underestimate tree response.

Altered leaf morphology, leaf resource dilution and defense chemistry induction in frost-defoliated aspen (Populus tremuloides)

St. Clair, S. B., Monson, S. D., Smith, E. A., Cahill, D. G., Calder, W. J. — Wed, 23 Sep 2009 05:35:47 PDT

In May 2007, a widespread frost event defoliated much of Utah’s high elevation aspen. About 5 weeks later, the frost-defoliated aspen produced a second leaf flush. The objective of this study was to characterize changes in leaf morphology and function in re-flush leaves following frost defoliation. Leaf size and thickness, photosynthesis, carbohydrate and nutrient status, and defense chemistry (phenolic glycosides and condensed tannins) were measured in first and second flush leaves. The second flush leaves produced two different morphological responses depending on frost damage severity. Severe frost damage was characterized by patchy canopy re-flushing with leaves that were on average four times larger than the first flush leaves. Moderate frost damage produced full canopy flushes with second flush leaves that were typically smaller than the first flush leaves. The second flush leaves tended to be thicker, and had significantly lower nutrient and sucrose concentrations, but had equal or higher rates of photosynthesis. These leaves showed a general pattern of defense chemistry induction with phenolic glycosides and condensed tannins increasing two- to threefold. Some of the changes in leaf morphology and defense chemistry observed in second flush leaves in 2007 persisted in leaves produced in the following year. We hypothesize that defense chemistry induction following abiotic defoliation serves as insurance against secondary defoliation events by herbivores that may further deplete nutrient and carbohydrate leaf resources below threshold points that are critical for physiological function. Resource dilution and allocation to secondary defense may place constraints on growth capacity.

Magnetic resonance microimaging indicates water diffusion correlates with dormancy induction in cultured hybrid poplar (Populus spp.) buds

Kalcsits, L., Kendall, E., Silim, S., Tanino, K. — Wed, 23 Sep 2009 05:35:47 PDT

Water content and mobility, which are factors known to be associated with dormancy induction in woody plants on a tissue level, were measured using non-destructive magnetic resonance microimaging (MRMI). Two cultured poplar clones (‘Okanese’ – temperature-insensitive dormancy and ‘Walker’ – temperature-sensitive dormancy) were subjected to dormancy differentiating temperature regimes, 18.5/3.5 °C and 18.5/13.5 °C (day/night), under a short photoperiod. Apparent diffusion coefficient, an indicator of water mobility, correlated with dormancy development in the axillary bud and vascular bud trace regions. In contrast, T₁ relaxation time, an indicator of static biophysical water properties, did not correlate significantly with dormancy in the regions that were examined. Although MRMI studies using T₁ relaxation measurements have dominated the phytological field, our work indicates that water mobility is an important factor in studies examining water changes during dormancy induction in the critical tissues of woody plants.

Cryopreservation of dormant European ash (Fraxinus excelsior) orthodox seeds

Chmielarz, P. — Wed, 23 Sep 2009 05:35:47 PDT

We investigated the sensitivity of dormant Polish-provenance Fraxinus excelsior L. seeds to extreme desiccation and liquid nitrogen (LN, –196 °C). Germination and seedling emergence tests revealed that the critical water content (WC) of the desiccated seeds was 0.04–0.06 g H₂O g^–1 dry mass, g g^–1 (0.04 g g^–1 in the germination test and 0.06 g g^–1 in the seedling emergence test). The seeds that were within the safe WC range (0.06–0.24 g g^–1 in the germination test and 0.08–0.24 g g^–1 in the seedling emergence test) tolerated freezing in LN. A 2-year seed storage period in LN after desiccation to a safe WC did not decrease the germination after thawing as compared with a 2-year seed storage at –3 °C. When the seeds were stored in LN after dormancy breaking, the germination rate after storage was lower, because the seeds had to be desiccated to the lower level (~ 0.11 g g^–1) within the seeds’ safe WC range after stratification (before storage). Secondary dormancy was induced in seeds that were desiccated after stratification. The results of this study confirm the feasibility of long-term cryopreservation of European ash seeds in forest gene banks.

Polyamine profiles and biosynthesis in somatic embryo development and comparison of germinating somatic and zygotic embryos of Norway spruce

Wed, 23 Sep 2009 05:35:47 PDT

The polyamine (PA) contents and activities of PA biosynthetic enzymes in Norway spruce somatic embryos [Picea abies L. (Karst.), genotype AFO 541] were studied in relation to anatomical changes during their development, from proliferation to germination, and changes in these variables associated with the germination of mature somatic and zygotic embryos were compared. Activities of PA biosynthetic enzymes steadily increased during the development of somatic embryos, from embryogenic suspensor mass until early cotyledonary stages. In these stages, the spermidine (Spd) level was significantly higher than the putrescine (Put) level, and the increases coincided with the sharp increases in S-adenosylmethionine decarboxylase activity in the embryos. The biosynthetic enzyme activity subsequently declined in mature cotyledonary embryos, accompanied by sharp reductions in PA contents, especially in cellular Put contents in embryos from 6 weeks old through the desiccation phase (although the spermine level significantly increased during the desiccation phase), resulting in a shift in the Spd/Put ratio from ca. 2 in early cotyledonary embryos to around 10 after 3 weeks of desiccation. In mature zygotic embryos, Spd contents were twofold lower, but Put levels were higher, than in mature somatic embryos, hence their Spd/Put ratio was substantially lower (ca. 2, in both embryos and megagametophytes). In addition, the PA synthesis activity profiles in the embryos differed (ornithine decarboxylase and arginine decarboxylase activities predominating in mature somatic and zygotic embryos, respectively). The start of germination was associated with a rise in PA biosynthetic activity in the embryos of both origins, which was accompanied by a marked increase in Put contents in somatic embryos, resulting in the decline of Spd/Put ratio to about 2, similar to the ratio in mature and germinating zygotic embryos. The accumulation of high levels of PAs in somatic embryos may be causally linked to their lower germinability than in zygotic embryos.

Cloning and functional characterization of an acyl-acyl carrier protein thioesterase (JcFATB1) from Jatropha curcas

Wed, 23 Sep 2009 05:35:47 PDT

A full-length cDNA of an acyl-acyl carrier protein (ACP) thioesterase (TE) (EC 3.1.2.14), named JcFATB1, was isolated from the woody oil plant Jatropha curcas L. The deduced amino acid sequence of the cDNA shares about 78% identity with FATB TEs, but only about 33% identity with FATA TEs from other plants. The deduced sequence also contains two essential residues (H³¹⁷ and C³⁵²) for TE catalytic activity and a putative chloroplast transit peptide at the N-terminal. Southern blot analysis revealed that a single copy of JcFATB1 is present in the J. curcas genome, and semi-quantitative PCR analysis showed that JcFATB1 was expressed in all tissues that were examined, most strongly in seeds, in which its expression peaked in late developmental stages. Seed-specific overexpression of the JcFATB1 cDNA in Arabidopsis resulted in increased levels of saturated fatty acids, especially palmitate, and in reduced levels of unsaturated fatty acids. The findings suggest that JcFATB1 from this woody oil plant can function as a saturated acyl-ACP TE and could potentially modify the seed oil of J. curcas to increase its levels of palmitate.