Tree Physiology Advance Access originally published online on December 5, 2008
Tree Physiology 2009 29(2):229-238; doi:10.1093/treephys/tpn020
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Adaptation of fine roots to annual fertilization and irrigation in a 13-year-old Pinus pinaster stand
1 ENITA de Bordeaux, UMR 1220 TCEM, F-33883 Villenave d’Ornon, France
2 Corresponding author (mark.bakker{at}bordeaux.inra.fr)
3 Faculté de foresterie, Université de Moncton, Campus d’Edmundston, 165 boulevard Hébert, Edmundston, Nouveau-Brunswick, Canada
4 INRA, UR 1263 EPHYSE, F-33612 Cestas, France
5 INRA, UMR 1220 TCEM, F-33883 Villenave d’Ornon, France
6 INRA, UMR 1222 BSR, F-34060 Montpellier, France
7 INRA, UPR 1264 MYCSA, F-33883 Villenave d’Ornon, France
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Abstract |
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Effects of fertilization and irrigation on fine roots and fungal hyphae were studied in 13-year-old maritime pine (Pinus pinaster Aït. in Soland), 7 years after the initiation of the treatments. The fertilization trials consisted of a phosphorus treatment, a complete fertilizer treatment (N, P, K, Ca and Mg), and an unfertilized treatment (control). Fertilizers were applied annually and were adjusted according to foliar target values. Two irrigation regimes (no irrigation and irrigation of a set amount each day) were applied from May to October. Root samples to depths of 120 cm were collected in summer of 2005, and the biomass of small roots (diameter 2–20 mm) and fine roots (diameter 
2 mm) and fine root morphology were assessed. Biomass and length of hyphae were studied by a mesh ingrowth bag technique. Total fine root biomass in the litter and in the 0–120 cm soil profile ranged between 111 and 296 g m–2. Results derived from the measurements of biomass and root length, or root area, showed that both fertilizer treatments reduced the size of the fine root system, especially in the top soil layers, but did not affect small roots. Compared with control treatments, fine root morphology was affected by both fertilizer treatments with the fine roots having increased specific root length/area, and irrigation tended to reinforce this finer morphology. The amount of hyphae in the mesh ingrowth bags was higher in the fertilization and irrigation treatments than in the controls, suggesting further extension of the root system (ectomycorrhizal infection) and thus of the uptake system. Irrigation had no significant effect on the size of the fine root system, but resulted in a shallower rooting system. Total root to shoot ratios were unaffected by the treatments, but fine root mass:needle mass and fine root area index:leaf area index ratios decreased with increasing nutrient supply. Overall, compared with the control fine roots, increased nutrient supply resulted in a lower fine root biomass but the dynamic fraction of the finest roots was greater. Irrigation had only limited effects on fine root size, distribution and morphology.
Keywords: annual resource optimization, fine root density, fine root morphology, hyphae, root to shoot ratios
Received June 26, 2008; Accepted September 30, 2008
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