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

Abstract

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.

Revisiting Global Vegetation Controls Using Multi‐Layer Soil Moisture

“…Li et al, 2018;Orth & Destouni, 2018;J. Wu et al, 2016;Yan et al, 2019). While the NDVI and NIRv analyses overall confirm the SIF results, they show extended water-related controls in arid regions and in tree-grass mixed regimes, consistent with previous findings (Walther et al, 2019).…”

“…In Figures 3d–3f we show that grasses and shrubs with a low fraction of tree cover are most water‐controlled, regions with intermediate tree cover are typically temperature‐controlled, and regions with the highest tree cover are mostly radiation‐controlled. Energy controls involve a relatively lower vulnerability of tree ecosystems to droughts than other ecosystems (Huang & Xia, 2019), as droughts are typically associated with above‐average solar radiation and newly developing leaves that can support photosynthesis (Hutyra et al., 2007; X. Li et al., 2018; Orth & Destouni, 2018; J. Wu et al., 2016; Yan et al., 2019). While the NDVI and NIRv analyses overall confirm the SIF results, they show extended water‐related controls in arid regions and in tree‐grass mixed regimes, consistent with previous findings (Walther et al., 2019).…”

Revisiting global vegetation controls using multi-layer soil moisture

“…Such main energy controls involve a relatively lower vulnerability of tree ecosystems to droughts than other ecosystems (Huang & Xia, 2019), as droughts are typically associated with above-average solar ESSOAr | https://doi.org/10.1002/essoar.10504463.1 | Non-exclusive | First posted online: Sat, 3 Oct 2020 09:53:39 | This content has not been peer reviewed. radiation and newly developing leaves that can compensate photosynthesis (Orth & Destouni, 2018;Yan et al, 2019;Hutyra et al, 2007;Wu et al, 2016;Li et al, 2018b). Moreover, consistent with the previous findings, NDVI and NIRv show extended significant water-related controls to tree-grass mixed biomes compared with the SIF results (Walther et al, 2019).…”

Fire dynamics in Mato Grosso State, Brazil: the relative roles of gross primary productivity

“…The highest occurrence of fires in 2010 in the Amazon biome is due to the severe drought that occurred in 2010 due to the El Niño-Southern Oscillation (ENSO) phenomenon, which was intensified by the warming of the tropical North Atlantic Ocean (Lewis, Brando, Phillips, Van Der Heijden, & Nepstad, 2011;Marengo, Soares, Tomasella, Alves, & Rodriguez, 2011). High burn rates in 2017 may also reflect El Niño 2015/2016 (Yan, Wang, Huete, & Shugart, 2019). Some authors have noted that El Niño events decrease rainfall and increase evaporation potential which leads to reduced soil moisture, which makes the forest more susceptible to burning (Lee et al, 2013;Doughty et al, 2015;Feldpausch et al, 2016;Liu et al, 2018).…”

“…Some authors have noted that El Niño events decrease rainfall and increase evaporation potential which leads to reduced soil moisture, which makes the forest more susceptible to burning (Lee et al, 2013;Doughty et al, 2015;Feldpausch et al, 2016;Liu et al, 2018). For Yan et al (2019) This mechanism of suppression of the photosynthetic rate by means of water deficit is one of the most important in the forests of the Amazon.…”