No Variation of Leaf-Level Water Use Efficiency Along the Fast-Slow Growth Spectrum in Amazonian Forest Trees
Julien Lamour1,2, Daisy C. Souza3, Bruno O. Gimenez,4, Niro Higuchi3, Jérôme Chave2, Jeffrey Chambers4,5, Alistair Rogers1* (firstname.lastname@example.org)
1Environmental and Climate Sciences Department, Brookhaven National Laboratory, Upton, NY; 2Evolution and Biological Diversity, French National Centre for Scientific Research/French National Research Institute for Sustainable Development/Université Paul Sabatier, Toulouse, France; 3Forest Management Laboratory, National Institute of Amazonian Research, Manaus, Amazonas, Brazil; 4Department of Geography, University of California–Berkeley, CA; 5Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, Berkeley, CA
Forest disturbance increases the proportion of fast-growing species compared to slow-growing species. These two species groups have different carbon storage capacities and different vulnerabilities to climate change. Understanding physiological differences between these groups is necessary to enabling their representation as separate plant functional types within Earth system models. This study analyzed leaf-level water-use efficiency—the marginal carbon gain of transpiration water loss which controls leaf gas exchange. Wood density was used as a proxy for the fast-slow growth spectrum to test whether low wood density trees (LWD) had a lower leaf water-use efficiency than trees with a high wood density (HWD). At one Amazonian forest site, in situ steady-state gas exchange measurements and leaf composition measurements were performed on sun-lit leaves of five LWD and five HWD species. LWD species invested more nitrogen in photosynthetic capacity than HWD species and had higher photosynthetic rates and higher stomatal conductance. However, the two groups had a comparable leaf water-use efficiency. This has implications for the physiology of tropical trees and for developing separate fast-growing and slow-growing plant functional types in Earth system models. The study also showed that waiting for steady-state gas-exchange markedly increased estimates of leaf water-use efficiency.