Canopy leaf abundance of Amazon rainforests increases in the dry season but decreases in the wet season, contrary to earlier expectations of water stress adversely affecting plant functions. Drivers of this seasonality, particularly the role of water availability, remain debated. We introduce satellite-based ecophysiological indicators to demonstrate that Amazon rainforests are constrained by water during dry seasons despite light-driven canopy greening. Evidence includes a shifted partitioning of photosynthetically active radiation toward more isoprene emissions and synchronized declines in leaf and xylem water potentials. In addition, we find that convective storms attenuate light-driven ecosystem greening in the late dry season and then reverse to net leaf loss in the wet season, improving rainforest leaf area predictability by 24 to 31%. These findings highlight the susceptibility of Amazon rainforests to increasing risks of drought and windthrow disturbances under warming.

中文翻译：

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缺水和风暴干扰共同调节亚马逊雨林的季节性


亚马逊雨林的冠层叶子丰度在旱季增加，但在雨季减少，这与之前关于水分胁迫会对植物功能产生不利影响的预期相反。这种季节性的驱动因素，特别是水资源供应的作用，仍然存在争议。我们引入基于卫星的生态生理指标来证明，尽管有光驱动的树冠绿化，但亚马逊雨林在旱季仍受到水的限制。证据包括光合有效辐射的分配转向更多的异戊二烯排放，以及叶片和木质部水势的同步下降。此外，我们发现对流风暴会削弱干季末光驱动的生态系统绿化，然后在湿季逆转为净叶损失，将雨林叶面积的可预测性提高 24% 至 31%。这些发现凸显了亚马逊雨林在气候变暖的情况下更容易遭受干旱和风扰的风险。