Abstract
AbstractHigh temperature, especially above 35oC, is known to reduce leaf photosynthetic rate in many tree species. This study investigated the effect of high temperature on isoprene-emitting (aspen) and non- emitting (birch) trees under ambient and elevated CO2 under open field conditions. Aspen trees tolerate heat better than birch trees and elevated CO2 protects both species against moderate heat stress. The increased thermotolerance in aspen trees compared to the birch trees may result from the aspen's ability to produce isoprene. Elevated CO2 increased carboxylation capacity, photosynthetic electron transport capacity and triose phosphate use in both birch and aspen trees. High temperature decreased all of these parameters in birch regardless of CO2 treatment but only photosynthetic electron transport and triose phosphate use at ambient CO2 were reduced in aspen. As temperature rises, non-isoprene-emitting trees will be at a disadvantage and biological diversity and species richness might be lost in some ecosystems. Our results indicate that isoprene emitting tree species will have an advantage over non-isoprene emitting ones under high temperatures.
Highlights
In the summer of 2006 we measured the effect of a natural prolonged heat spell on photosynthesis of aspen and birch trees growing in Free Air Carbon dioxide Enrichment (FACE) rings
There was no evidence of heat stress in both aspen and birch at temperature range of 3235oC, but at 36-39oC birch trees showed visible symptoms of heat stress through yellowing of leaves and leaf shedding (Fig. 1), and invisible symptoms through decreased Vcmax, triose phosphate use (TPU), J and gs (Fig. 2 and Table 1)
Elevated CO2 increased the thermotolerance in both aspen and birch trees at leaf temperatures ranging from 36-39oC and in aspen leaf temperatures to 40-41oC (Figure 2). In both aspen and birch trees, there was a significant increase in Vcmax, J and TPU and no significant change in gs under elevated CO2 at leaf temperatures of 36-39oC (Table 1)
Summary
In the summer of 2006 we measured the effect of a natural prolonged heat spell on photosynthesis of aspen and birch trees growing in Free Air Carbon dioxide Enrichment (FACE) rings. High temperatures are reported to decrease carbon assimilation rate in a number of different tree species[1,2,3].
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