Summary As temperature rises, net carbon uptake in tropical forests decreases, but the underlying mechanisms are not well understood. High temperatures can limit photosynthesis directly, for example by reducing biochemical capacity, or indirectly through rising vapor pressure deficit (VPD) causing stomatal closure. To explore the independent effects of temperature and VPD on photosynthesis we analyzed photosynthesis data from the upper canopies of two tropical forests in Panama with Generalized Additive Models. Stomatal conductance and photosynthesis consistently decreased with increasing VPD, and statistically accounting for VPD increased the optimum temperature of photosynthesis (Topt) of trees from a VPD‐confounded apparent Topt of c. 30–31°C to a VPD‐independent Topt of c. 33–36°C, while for lianas no VPD‐independent Topt was reached within the measured temperature range. Trees and lianas exhibited similar temperature and VPD responses in both forests, despite 1500 mm difference in mean annual rainfall. Over ecologically relevant temperature ranges, photosynthesis in tropical forests is largely limited by indirect effects of warming, through changes in VPD, not by direct warming effects of photosynthetic biochemistry. Failing to account for VPD when determining Topt misattributes the underlying causal mechanism and thereby hinders the advancement of mechanistic understanding of global warming effects on tropical forest carbon dynamics.

中文翻译：

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对蒸气压不足的气孔响应驱动热带森林光合作用的表观温度响应

概括 随着温度升高，热带森林的净碳吸收量减少，但其潜在机制尚不清楚。高温可以直接限制光合作用，例如通过降低生化能力，或通过增加蒸气压不足（VPD）导致气孔关闭来间接限制光合作用。 为了探索温度和 VPD 对光合作用的独立影响，我们使用广义加性模型分析了巴拿马两个热带森林上层树冠的光合作用数据。 气孔导度和光合作用随着 VPD 的增加而持续下降，并且统计 VPD 增加了光合作用的最适温度（时间选择）来自 VPD 混杂表观的树木时间选择的C。 30–31°C 至独立于 VPD时间选择的C。 33–36°C，而藤本植物则不依赖于 VPD时间选择达到测量温度范围内。尽管年平均降雨量相差 1500 毫米，但两片森林中的树木和藤本植物表现出相似的温度和 VPD 响应。 在生态相关的温度范围内，热带森林的光合作用主要受到以下因素的限制：间接变暖的影响是通过 VPD 的变化而不是通过直接的光合生物化学的变暖效应。确定时未考虑 VPD时间选择错误地归因了潜在的因果机制，从而阻碍了对全球变暖对热带森林碳动态影响的机制理解的进展。