Tree Physiology Advance Access published online on May 14, 2009
Tree Physiology, doi:10.1093/treephys/tpp033
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Emissions of volatile organic compounds and leaf structural characteristics of European aspen (Populus tremula) grown under elevated ozone and temperature
1 Department of Environmental Science, University of Kuopio, P.O. Box 1627, FI-70211 Kuopio, Finland
2 Corresponding author (kaisa.hartikainen{at}uku.fi)
3 Faculty of Biosciences, University of Joensuu, P.O. Box 111, FI-80101 Joensuu, Finland
4 The Finnish Forest Research Institute, Vantaa Research Unit, FI-01301 Vantaa, Finland
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Abstract |
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Northern forest trees are challenged to adapt to changing climate, including global warming and increasing tropospheric ozone (O3) concentrations. Both elevated O3 and temperature can cause significant changes in volatile organic compound (VOC) emissions as well as in leaf anatomy that can be related to adaptation or increased stress tolerance, or are signs of damage. Impacts of moderately elevated O3 (1.3x ambient) and temperature (ambient + 1 °C), alone and in combination, on VOC emissions and leaf structure of two genotypes (2.2 and 5.2) of European aspen (Populus tremula L.) were studied in an open-field experiment in summer 2007. The impact of O3 on measured variables was minor, but elevated temperature significantly increased emissions of total monoterpenes and green leaf volatiles. Genotypic differences in the responses to warming treatment were also observed. 
-Pinene emission, which has been suggested to protect plants from elevated temperature, increased from genotype 5.2 only. Isoprene emission from genotype 2.2 decreased, whereas genotype 5.2 was able to retain high isoprene emission level also under elevated temperature. Elevated temperature also caused formation of thinner leaves, which was related to thinning of epidermis, palisade and spongy layers as well as reduced area of palisade cells. We consider aspen genotype 5.2 to have better potential for adaptation to increasing temperature because of thicker photosynthetic active palisade layer and higher isoprene and -pinene emission levels compared to genotype 2.2. Our results show that even a moderate elevation in temperature is efficient enough to cause notable changes in VOC emissions and leaf structure of these aspen genotypes, possibly indicating the effort of the saplings to adapt to changing climate.
Keywords: -Pinene, epidermis, green leaf volatiles, isoprene, leaf anatomy, mesophyll tissue, microscopy, monoterpenes
Received February 2, 2009; Accepted April 20, 2009