Leaf MeOH and AA emission responses to CO2, light, and temperature
In order to evaluate the effect of environmental conditions on well hydrated poplar branches at the leaf level, MeOH and AA emissions, AA/MeOH ratio, stomatal conductance (gs), transpiration, and net photosynthesis (Pnet) measurements occurred in parallel during CO2, light, and temperature leaf response studies. To minimize leaf water stress, poplar branches were detached, recut under water, with the target leaf placed in the chamber and the rest of the branch placed in a hydrated atmosphere in the dark. In this way, leaf hydration was maximized by shutting down transpiration from all leaves on the branch except the leaf inside the dynamic leaf chamber. Across the CO2(Anet-Ci, Fig. 4a-c ), light (Anet-PAR, Fig. 4d-f ), and temperature (Anet-leaf temp., Fig. 4g-i ) response curves, MeOH and AA emissions generally tracked patterns of gsand E, and did not appear to be strongly dependent on Anet. For example, at low Ci, MeOH emissions tended to increase with gs and decrease with gs at high Ci. However, during the light curves, gs values remained high and increased only slightly as a function of PAR, while MeOH and AA emissions also remained relatively stable. In contrast, as leaf temperature increased, gs increased up to 35-37 °C before declining at higher temperatures, while MeOH and AA emissions together with transpiration generally increased up to the highest leaf temperatures (40 °C). While gscontinued to decline in the dark at 40 °C, leaf dark respiration caused Anet to quickly drop to negative values. In contrast, MeOH and AA emissions did not show a fast decline in the dark, but rather declined more gradually together with gs and E. Importantly across Ci and PAR response curves, leaf AA/MeOH emission ratios remained relatively stable with maximum values < 10%. In contrast, AA/MeOH emission ratios increased as a function of temperature reaching maximum values in the light at 40 °C of 10-20%.