Effects of Light Component and Water Stress on Photosynthesis of Amazon Rainforests During the 2015/2016 El Niño Drought

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Journal Article
Journal of Geophysical Research: Biogeosciences, 2019, 124 (6), pp. 1574 - 1590
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©2019. American Geophysical Union. All Rights Reserved. Whether enhanced sunshine increases photosynthesis in Amazon rainforests during drought is unclear. Here we used a light component-based two-leaf-photosynthesis model, driven with climate data and satellite vegetation data, to inspect the controlling mechanisms among climate factors on gross primary production (GPP) during the 2015/2016 El Niño drought event. We found that simulated GPP and Moderate Resolution Imaging Spectroradiometer enhanced vegetation index indicated an Amazonian “browning” and not a “green up” during the 2015/2016 El Niño year relative to the 2011–2014 interval. The result shows that, along with intensified sunlight, diffuse sunlight and diffuse fraction as well as canopy light use efficiency decreased, which further produced a decreased potential GPP* (determined by light components and leaf area index of shaded and sunlit leaves). The decreased GPP* and drought-induced water stress jointly reduced canopy photosynthesis of Amazon rainforests during the 2015/2016 drought. The light component variations caused a reduction in GPP but with a magnitude inferior to the GPP reduction from water stress. These findings suggest that intensified sunlight did not enhance photosynthesis of Amazon rainforests and highlight the important role of light components in interannual and seasonal variations of photosynthesis in Amazon rainforests.
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