Hydraulically-vulnerable trees survive on deep-water access during droughts in a tropical forest

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Rutuja Chitra-Tarak, Earth and Environmental Sciences Division, Los Alamos National Lab, Los Alamos, NM, Rutuja Chitra-Tarak, Smithsonian Environmental Research Center, Smithsonian Institution Forest Global Earth Observatory, Edgewater, MD, Chonggang Xu, Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, Salomon Aguilar, Kristina J. Anderson-Teixeira, Matteo Detto, Norbert Kunert, Steven R. Paton, Rolando Perez and Sean M. McMahon, Smithsonian Tropical Research Institute, Panama, Kristina J. Anderson-Teixeira, Smithsonian Conservation Biology Institute, Front Royal, VA, Jeffrey Chambers, Earth Sciences Division, Climate Sciences Department, Lawrence Berkeley National Laboratory, Berkeley, CA, Matteo Detto, Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, Boris Faybishenko, Lawrence Berkeley National Laboratory, Berkeley, CA, Rosie A. Fisher, Climate & Global Dynamics, National Center for Atmospheric Research, Boulder, CO, Rosie A. Fisher, Laboratoire Évolution & Diversité Biologique CNRS:UMR 5174, Université Paul Sabatier, Toulouse, France, Ryan Knox, Earth Sciences Division, Lawrence Berkeley National Lab, Charles D. Koven, Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, Berkeley, CA, Lara Kueppers, Energy and Resources Group, University of California, Berkeley, Berkeley, CA, Norbert Kunert, Institute of Botany, Department of Integrative Biology and Biodiversity Research, University of Natural Resources and Life Sciences Vienna, Wien, Austria, Norbert Kunert and Joseph Zailaa, Conservation Ecology Center, Smithsonian Conservation Biology Institute, Front Royal, VA, Stephan Kupers, Computational Forest Ecology, German Centre for Integrative Biodiversity Research (iDiv), Leipzig, Germany, Nathan McDowell, Atmospheric Sciences & Global Change, Pacific Northwest National Laboratory, Richland, WA, Brent D. Newman, Earth & Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, Laurent Ruiz, Indo-French Cell for Water Sciences, Indian Institute of Science, Bangalore, India, Laurent Ruiz, CNRS, UPS, UMR GET, IRD, Toulouse, France, Laurent Ruiz, Institut Agro, UMR SAS, INRAE, Rennes, France, Lawren Sack, Department of Ecology & Evolutionary Biology, University of California Los Angeles, Los Angeles, CA, Jeffrey M. Warren, Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN, Brett T. Wolfe, School of Natural Resources and Management, Louisiana State University, Baton Rouge, LA, Brett T. Wolfe, Smithsonian Tropical Research Institute, Gamboa, Panama, Cynthia L. Wright, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, Joseph Zailaa, Biological Sciences Department, California State University, Los Angeles, Sean M. McMahon, Smithsonian Institution Forest Global Earth Observatory, Smithsonian Environmental Research Center, Edgewater, MD

Background/Question/Methods



• Deep-water access is arguably the most effective, but under-studied mechanism that plants employ to survive during drought. Vulnerability to embolism and hydraulic safety margins can predict mortality risk at given levels of dehydration, but deep-water access may delay plant dehydration. Here, we tested the role of deep-water access in enabling survival within a diverse tropical forest community in Panama using a novel data-model approach.
• We inversely estimated the effective rooting depth (ERD, as the average depth of water extraction), for 32 canopy species by linking diameter growth dynamics (1990-2015) to vapor pressure deficit, water potentials in the whole-soil column, and leaf hydraulic vulnerability curves. We validated ERD estimates against existing isotopic data of potential water-access depths.





Results/Conclusions



• Across species, deeper ERD was associated with higher maximum stem hydraulic conductivity, greater vulnerability to xylem embolism, narrower safety margins, and lower mortality rates during extreme droughts over 35 years (1981-2015), especially in evergreen species. Species exposure to water-stress declined with deeper ERD indicating that trees compensate for water-stress related mortality risk through deep-water access.
• The role of deep-water access in mitigating mortality of hydraulically vulnerable trees has important implications for our predictive understanding of forest dynamics under current and future climates.