THE RESPONSE OF ISOPRENE EMISSION RATE AND PHOTOSYNTHETIC RATE TO PHOTON FLUX AND NITROGEN SUPPLY IN ASPEN AND WHITE OAK TREES

Isoprene is the primary biogenic hydrocarbon emitted from temperate de ciduous forest ecosystems, The effects of varying photon flux density (PFD) and nitrogen growth regimes on rates of isoprene emission and ne t photosynthesis in potted aspen and white oak trees are reported, In both aspen and oak trees, whether rates were expressed on a leaf area or dry mass basis, (1) growth at higher PFD resulted in significantly higher rates of isoprene emission, than growth at lower PFD, (2) there is a significant positive relationship between isoprene emission rate and leaf nitrogen concentration in both sun and shade trees, and (3) there is a significant positive correlation between isoprene emission rate and photosynthetic rate in both sun and shade trees, The greater capacity for isoprene emission in sun leaves was due to both higher le af mass per unit area and differences in the biochemical and/or physio logical properties that influence isoprene emission, Positive correlat ions between isoprene emission rate and leaf nitrogen concentration su pport the existence of mechanisms that link leaf nitrogen status to is oprene synthase activity, Positive correlations between isoprene emiss ion rate and photosynthesis rate support previous hypotheses that isop rene emission plays a role in protecting photosynthetic mechanisms dur ing stress.