Disentangling the Effect of Humidity and Temperature in the Leaf Conductance Response to Vapor Deficit in Tropical Trees
Authors
Alistair Rogers1,7* (arogers@bnl.gov), Julien Lamour1,2, Kenneth J. Davidson1,3, Jérôme Chave2, Martijn Slot4, Jeffrey Chambers5,6, Shawn P. Serbin1,6
Institutions
1Environmental and Climate Sciences Department, Brookhaven National Laboratory, Upton, NY; 2Evolution and Biological Diversity (EDB), CNRS/IRD/UPS, Toulouse, France; 3Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY; 4Smithsonian Tropical Research Institute, Panama City, Panama; 5Department of Geography, University of California–Berkeley, CA; 6Lawrence Berkeley National Laboratory, Berkeley, CA; 6Goddard Space Flight Center, NASA, Greenbelt, MD; 7Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA
URLs
Abstract
Understanding the response of stomata to changes in air temperature and humidity is key to predicting the future of tropical forests. Models that describe the behavior of stomata need to represent the response to rising temperature and drier air (a higher vapor pressure deficit) but differ in their approaches. The team examined the response of stomatal conductance to independent changes in temperature and relative humidity in five tropical tree species by manipulating leaf-level conditions using photosynthetic gas exchange analyzers. Researchers compared six formulations of steady-state conductance models that used different representations of photosynthesis and the evaporative demand on conductance. The team found that the best-fitting model used a nonlinear relationship between photosynthesis and stomatal conductance. Using relative humidity instead of vapor pressure deficit improved model performance when the temperature varied and resulted in similar performance when the humidity varied. The different stomatal conductance dynamics to changes in humidity and temperature showed that the underlying mechanisms associated with the stomatal response may be different. Moreover, the nonlinear relationship between photosynthetic rate and stomatal conductance suggests a sharper physiological response of tropical forests to extreme climatic conditions than previously acknowledged.