Effects of the 2015 El-Niño extreme drought on the sapflow of trees in eastern Amazonia
Thursday, 9 June 2016
Mauro Brum Jr.1,2, Rafael S. Oliveira2, Jose Gutierrez3, Julian Licata4, Thomas G Pypker5 and Heidi Asbjornsen3, (1)UNICAMP, Campinas, Brazil, (2)UNICAMP State University of Campinas, Campinas, Brazil, (3)University of New Hampshire Main Campus, Durham, NH, United States, (4)National Institute of Agropecuary Technology (INTA), Concordia, Argentina, (5)Thompson Rivers University, Kamloops, BC, Canada
Abstract:
The 2015 El-Niño (ENSO) has imposed one of the strongest droughts ever recorded in eastern Amazonia. Extreme droughts might increase the risk of tree mortality by hydraulic failure of drought sensitive species and negatively impact ecosystem water fluxes. We evaluated how unusually high atmospheric vapour pressure deficit and low soil water content (SWC) conditions observed during the 2015 ENSO event affected the daily and seasonal dynamics of tree sap-flux-density (Js) for species with contrasting vulnerabilities to drought. In general, tree Js increased exponentially with VPD and reach an asymptote point (usually when VPD between -1 to -2 kPA). However, some species showed a hump-shape curve that better explain this relationship, suggesting that these species control water loss under high evaporative demand to avoid hydraulic failure. When we contrasted JsxVPD curves between the driest and wettest month, the asymptote point have changed for some species. Our results suggest that sapflow data can be used to classify the degree of isohydry of species. Trees showing a hump-curve on JsxVPD relationship tend to be more isohydric because they reduce water use when exposed to higher VPDs. In contrast, trees that keep the transpiration after the asymptote point are more anisohydric due the maintanance of transpiration in high VPD. Drought sensitive species showed a decrease on Js, while others maintained constant transpiration rates throughout the seasons. We discuss the role of hydraulic traits and rooting depth on tree Js dynamics during extreme droughts.
