Mechanisms of water supply and vegetation demand govern the seasonality and magnitude of evapotranspiration in Amazonia and Cerrado

Bradley O. Christoffersen, Natalia Restrepo-Coupe, M. Altaf Arain, Ian T. Baker, Bruno P. Cestaro, Phillippe Ciais, Joshua B. Fisher, David Galbraith, Xiaodan Guan, Lindsey Gulden, Bart van den Hurk, Kazuhito Ichii, Hewlley Imbuzeiro, Atul Jain, Naomi Levine, Gonzalo Miguez-Macho, Ben Poulter, Debora R. Roberti, Koichi Sakaguchi, Alok SahooKevin Schaefer, Mingjie Shi, Hans Verbeeck, Zong Liang Yang, Alessandro C. Araújo, Bart Kruijt, Antonio O. Manzi, Humberto R. da Rocha, Celso von Randow, Michel N. Muza, Jordan Borak, Marcos H. Costa, Luis Gustavo Gonçalves de Gonçalves, Xubin Zeng, Scott R. Saleska

Research output: Contribution to journalArticle

50 Scopus citations

Abstract

Evapotranspiration (E) in the Amazon connects forest function and regional climate via its role in precipitation recycling However, the mechanisms regulating water supply to vegetation and its demand for water remain poorly understood, especially during periods of seasonal water deficits In this study, we address two main questions: First, how do mechanisms of water supply (indicated by rooting depth and groundwater) and vegetation water demand (indicated by stomatal conductance and intrinsic water use efficiency) control evapotranspiration (E) along broad gradients of climate and vegetation from equatorial Amazonia to Cerrado, and second, how do these inferred mechanisms of supply and demand compare to those employed by a suite of ecosystem models? We used a network of eddy covariance towers in Brazil coupled with ancillary measurements to address these questions With respect to the magnitude and seasonality of E, models have much improved in equatorial tropical forests by eliminating most dry season water limitation, diverge in performance in transitional forests where seasonal water deficits are greater, and mostly capture the observed seasonal depressions in E at Cerrado However, many models depended universally on either deep roots or groundwater to mitigate dry season water deficits, the relative importance of which we found does not vary as a simple function of climate or vegetation In addition, canopy stomatal conductance (gs) regulates dry season vegetation demand for water at all except the wettest sites even as the seasonal cycle of E follows that of net radiation In contrast, some models simulated no seasonality in gs, even while matching the observed seasonal cycle of E. We suggest that canopy dynamics mediated by leaf phenology may play a significant role in such seasonality, a process poorly represented in models Model bias in gs and E, in turn, was related to biases arising from the simulated light response (gross primary productivity, GPP) or the intrinsic water use efficiency of photosynthesis (iWUE). We identified deficiencies in models which would not otherwise be apparent based on a simple comparison of simulated and observed rates of E. While some deficiencies can be remedied by parameter tuning, in most models they highlight the need for continued process development of belowground hydrology and in particular, the biological processes of root dynamics and leaf phenology, which via their controls on E, mediate vegetation-climate feedbacks in the tropics.

Original languageEnglish (US)
Pages (from-to)33-50
Number of pages18
JournalAgricultural and Forest Meteorology
Volume191
DOIs
StatePublished - Jun 15 2014

Keywords

  • Canopy stomatal conductance
  • Deep roots
  • Evapotranspiration
  • Groundwater
  • Intrinsic water use efficiency
  • Tropical forest

ASJC Scopus subject areas

  • Forestry
  • Global and Planetary Change
  • Agronomy and Crop Science
  • Atmospheric Science

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    Christoffersen, B. O., Restrepo-Coupe, N., Arain, M. A., Baker, I. T., Cestaro, B. P., Ciais, P., Fisher, J. B., Galbraith, D., Guan, X., Gulden, L., van den Hurk, B., Ichii, K., Imbuzeiro, H., Jain, A., Levine, N., Miguez-Macho, G., Poulter, B., Roberti, D. R., Sakaguchi, K., ... Saleska, S. R. (2014). Mechanisms of water supply and vegetation demand govern the seasonality and magnitude of evapotranspiration in Amazonia and Cerrado. Agricultural and Forest Meteorology, 191, 33-50. https://doi.org/10.1016/j.agrformet.2014.02.008