B129-07
How do tropical trees alter below-ground dynamics in response to long-term drought: Results after four-years of rainfall exclusion
Thursday, 17 December 2020: 07:24
Virtual
Alexandria Lynn Pivovaroff1, Nathan McDowell2, Riley Leff2, Weibin Li2, Heather Pacheco2, Wenzhi Wang2, Peipei Zhang3, Charlotte Grossiord4, Lucas A Cernusak5, F. Yoko Ishida6, Susan Laurance7, Michael J Liddell8, Tayana Barrozo Rodrigues9, Kolby Jardine10, Israel de Jesus Sampaio-Filho Sr.11, Daisy Souza9, Timothy Brodribb12 and Jeffrey Q Chambers13, (1)Pacific Northwest National Laboratory, Atmospheric Sciences and Global Change Division, Richland, WA, United States, (2)Pacific Northwest National Laboratory, Richland, WA, United States, (3)Pacific Northwest National Laboratory, Richland, United States, (4)WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf, Switzerland, (5)James Cook University, College of Science and Engineering, Cairns, QLD, Australia, (6)James Cook University, Cape Tribulation, Australia, (7)James Cook University, College of Science and Engineering, Cairns, Australia, (8)Discipline of Chemistry & Centre for Tropical Environmental and Sustainable Sciences, James Cook University, Cairns, Qld, Australia, Cairns, Australia, (9)INPA National Institute of Amazonian Research, Manaus, Brazil, (10)Lawrence Berkeley National Laboratory, Climate and Ecosystem Sciences Division, Berkeley, CA, United States, (11)National Institute of Amazonian Research, Manaus, Brazil, (12)University of Tasmania, Hobart, Australia, (13)University of California, Berkeley, CA, United States
Abstract:
Tropical forests are responsible for about half of the terrestrial gross primary productivity on Earth. However, climate change and associated droughts are affecting tropical forests across the globe. Droughts have historically resulted in increased canopy tree death in the tropics, affecting community structure and biogeochemical cycles. Gas exchange and hydraulic traits, such as stomatal conductance and water potential, may be sensitive to droughts. We investigated the response of 11 canopy tree species in the Daintree Rainforest in Australia to an experimentally imposed 4-year drought, where rainfall exclusion shelters intercepted 80% of precipitation and soil water content was reduced by 40%. Our objective was to test the impacts of drought on changes in hydraulic and carbon traits in the context of tree mortality in a moist tropical forest.
We measured leaf-level gas exchange, water potentials, leaf functional traits, pressure-volume curves, non-structural carbohydrates, abscisic acid, and xylem vessel anatomy traits at the end of the wet season (November) in 2018 and the end of the dry season (May) in 2019. We found that there were no differences in any measured trait between the control and drought treatment despite the large difference in soil water content. However, some individual species did shift traits in response to the drought, with these responses being species-specific. The lack of major shifts in above-ground traits in response to significantly reduced water availability suggested that there were below-ground changes, which we investigated by utilizing a model that assumes that plant gas exchange maximizes that difference between photosynthetic gain and hydraulic risk. We used transpiration, and predawn and midday water potentials to evaluate the model outputs. Results indicated that droughted tree shifted rooting depth to increase access to below-ground water and maintain homeostatic water and carbon status regardless of precipitation. This evidence reveals that some tropical trees may have resilient strategies such as changes in below-ground water acquisition for responding to climate change.
