The effect of warming on tropical forest gas exchange.
Chris
Doughty, UC Irvine, cdoughty@uci.edu
(Presenting)
Mike
Goulden, UC Irvine, mgoulden@uci.edu
Scott
Miller, SUNY Albany, sdmiller@uci.edu
Humberto
da Rocha, Uuniversity of Sao Paulo, humberto@model.iag.usp.br
Further research is required to understand the sensitivity of tropical forest to climate warming. Previous research has shown that tropical forest photosynthesis decreases and respiration increases at high leaf temperatures and that tree growth is reduced in years with higher average air temperatures (Clark et al 2003). Models indicate that the climate related destruction of the Amazon forest will amplify global warming by 1.5˚ C, resulting in a mean temperature increase of 5.5˚ C, as compared with 4˚ C without this carbon cycle feedback (Cox et al 2000). These studies demonstrate the importance of temperature on tropical forest gas exchange. At the LBA Tapajos km 83 site we determined what controls tropical leaf temperature and how temperature affects photosynthesis and respiration. Sunlit leaves were substantially warmer than air temperatures and this had a negative effect on photosynthesis and stomatal conductance. We used eddy flux data to compare intervals of 10 minute cloudy periods followed by 20 minute sunny periods to see if similar trends could be seen at both the leaf and canopy level. The longer the sunny interval the warmer the canopy became and canopy conductance and CO2 exchange declined correspondingly. As the canopy warmed u* increased which increased turbulence and kept the canopy temperature from rising more. Long light intervals can cause heat stress in tropical forests but due to the very cloudy nature of the tropics such intervals are rare. However, if the tropics become both warmer and less cloudy such heat stress will increase.