Tropical forests are experiencing unprecedented high-temperature conditions due to climate change that could limit their photosynthetic functions. We studied the high-temperature sensitivity of photosynthesis in a rainforest site in southern Amazonia, where some of the highest temperatures and most rapid warming in the Tropics have been recorded. The quantum yield (F_v/F_m) of photosystem II was measured in seven dominant tree species using leaf discs exposed to varying levels of heat stress. T₅₀ was calculated as the temperature at which F_v/F_m was half the maximum value. T₅ is defined as the breakpoint temperature, at which F_v/F_m decline was initiated. Leaf thermotolerance in the rapidly warming southern Amazonia was the highest recorded for forest tree species globally. T₅₀ and T₅ varied between species, with one mid-storey species, Amaioua guianensis, exhibiting particularly high T₅₀ and T₅ values. While the T₅₀ values of the species sampled were several degrees above the maximum air temperatures experienced in southern Amazonia, the T₅ values of several species are now exceeded under present-day maximum air temperatures.

中文翻译：

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亚马逊东南部树木的光合量子效率可能已经受到气候变化的影响

由于气候变化，热带森林正在经历前所未有的高温条件，这可能会限制它们的光合作用功能。我们研究了亚马逊南部雨林地区光合作用的高温敏感性，那里记录了热带地区的一些最高温度和最迅速的变暖。使用暴露于不同热应力水平的叶盘，在七种优势树种中测量了光系统 II的量子产率 ( F _v / F _m )。T ₅₀计算为F _v / F _m为最大值一半时的温度。Ť ₅定义为断点温度，在该温度下F _v / F _m开始下降。迅速变暖的亚马逊南部的叶子耐热性是全球森林树种记录的最高值。T ₅₀和T _{5 因}物种而异，其中一种中层物种Amaioua guianensis表现出特别高的T ₅₀和T ₅值。虽然采样物种的T ₅₀值比亚马逊南部经历的最高气温高几度，但T ₅ 在目前的最高气温下，现在已经超过了几种物种的数值。