2024 Abstracts

Regulation of Whole-Tree Crown Conductance in Tropical Forests Across a Steep Climatic Gradient


Mizanur Rahman1* (mizanur.rahman@pnnl.gov), Nate McDowell1,2, Alistair Rogers3, Shawn Serbin3, Kim Ely3, Ken Davidson3, Jean-Christophe Domec4, Julien Lamour5, Sean Michaletz6, Brett Wolfe7, Alexandria Pivovaroff8, Alfonso Zambrano9, Joe Wright9, Jeffrey Chambers10,11


1Pacific Northwest National Laboratory, Richland, WA; 2Washington State University, Pullman, WA; 3Brookhaven National Laboratory, Upton, NY; 4Department of Forestry, Bordeaux Sciences Agro INRAE, Gradignan, France; 5French National Centre for Scientific Research, Toulouse, France; 6The University of British Columbia, Vancouver, Canada; 7Louisiana State University Agricultural Center, Baton Rouge, LA; 8Biology Division, Glendale Community College, Glendale, CA; 9Smithsonian Tropical Research Institute, Panama City, Panama; 10Lawrence Berkeley National Laboratory, Berkeley, CA; 11University of California–Berkeley, CA



Transpiration is strongly regulated by crown conductance but the mechanisms underlying variation in crown conductance are poorly understood in hyper-diverse tropical wet forests. Understanding this regulation is key to prediction of tree responses to climate changes. The team tested hypotheses regarding functional trait and environmental impacts on crown conductance at three forests across a moisture gradient in Panama. Crown conductance and its sensitivity to vapor pressure deficit (VPD) were among the highest ever measured globally.

Location along the moisture gradient, leaf phenology, and shade tolerance were not good predictors of transpiration or crown conductance. Trees from all three sites exhibited consistent responses of crown conductance and its sensitivity to VPD to soil moisture content but were less responsive to other climate variables. Similarly, crown conductance increased strongly with the degree of anisohydry. However, crown conductance response to whole-tree hydraulic conductance is site and season specific (significant positive relation only in the dry season and at the wet site). Crown conductance and its sensitivity to VPD exhibited consistent relationships with soil water content, the degree of anisohydry, and whole-tree hydraulic conductance. Future increases in VPD and drought will reduce crown conductance with large implications on water use and carbon uptake.