Tropical canopies are complex, with multiple canopy layers and pronounced gap dynamics contributing to their high species diversity and productivity. An important reason for this complexity is the large variation in shade tolerance among different tree species. At present, we lack a clear understanding of which plant traits control this variation, e.g., regarding the relative contributions of whole-plant versus leaf traits or structural versus physiological traits. We investigated a broad range of traits in six tropical montane rainforest tree species with different degrees of shade tolerance, grown under three different radiation regimes (under the open sky or beneath sparse or dense canopies). The two distinct shade-tolerant species had higher fractional biomass in leaves and branches while shade-intolerant species invested more into stems, and these differences were greater under low radiation. Leaf respiration and photosynthetic light compensation point did not vary with species shade tolerance, regardless of radiation regime. Leaf temperatures in open plots were markedly higher in shade-tolerant species due to their low transpiration rates and large leaf sizes. Our results suggest that interspecific variation in shade tolerance of tropical montane trees is controlled by species differences in whole-plant biomass allocation strategy rather than by difference in physiological leaf traits determining leaf carbon balance at low radiation.

中文翻译：

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控制热带山地树木耐荫性的性状

热带林冠是复杂的，具有多个林冠层和明显的间隙动态，从而促进了其较高的物种多样性和生产力。这种复杂性的重要原因是不同树种之间的耐荫性差异很大。目前，我们对哪些植物性状控制这种变异缺乏清晰的了解，例如，关于整株植物与叶片性状的相对贡献或结构植物与生理性状的相对贡献。我们调查了三种在不同辐射条件下（在开阔天空下或在稀疏或密密的树冠下）生长的六种具有不同程度的耐荫性的热带山地雨林树种的广泛性状。这两种不同的耐荫物种在叶片和树枝中的生物量分数较高，而耐荫物种在茎上的投入更多，在低辐射下这些差异更大。叶片的呼吸和光合作用的光补偿点不随物种遮荫能力而变化，而与辐射方式无关。由于低蒸腾速率和大叶片尺寸，开阔地带的叶片温度在耐荫物种中明显更高。我们的结果表明，热带山地树木的耐荫性种间差异是由全植物生物量分配策略中的物种差异控制的，而不是由决定低辐射下叶片碳平衡的生理叶片性状的差异控制的。由于低蒸腾速率和大叶片尺寸，开阔地带的叶片温度在耐荫物种中明显更高。我们的结果表明，热带山地树木的耐荫性种间差异是由全植物生物量分配策略中的物种差异控制的，而不是由决定低辐射下叶片碳平衡的生理叶片性状的差异控制的。由于低蒸腾速率和大叶片尺寸，开阔地带的叶片温度在耐荫物种中明显更高。我们的结果表明，热带山地树木的耐荫性种间差异是由全植物生物量分配策略中的物种差异控制的，而不是由决定低辐射下叶片碳平衡的生理叶片性状的差异控制的。