• Forests harbour large spatiotemporal heterogeneity in canopy structure. This variation drives the microclimate and light availability at the forest floor. So far, we do not know how light availability and sub-canopy temperature interactively mediate the impact of macroclimate warming on understorey communities.
• We therefore assessed the functional response of understorey plant communities to warming and light addition in a full factorial experiment installed in temperate deciduous forests across Europe along natural microclimate, light and macroclimate gradients. Furthermore, we related these functional responses to the species’ life-history syndromes and thermal niches.
• We found no significant community responses to the warming treatment. The light treatment, however, had a stronger impact on communities, mainly due to responses by fast-colonizing generalists and not by slow-colonizing forest specialists. The forest structure strongly mediated the response to light addition and also had a clear impact on functional traits and total plant cover.
• The effects of short-term experimental warming were small and suggest a time-lag in the response of understorey species to climate change. Canopy disturbance, for instance due to drought, pests or logging, has a strong and immediate impact and particularly favours generalists in the understorey in structurally complex forests.

中文翻译：

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森林林下群落对光与森林结构的相互作用反应强烈，但对小气候变暖没有反应

• 森林在冠层结构中具有很大的时空异质性。这种变化推动了森林地面的小气候和光照可用性。到目前为止，我们还不知道光照可用性和冠层下温度如何交互调节大气候变暖对下层社区的影响。
• 因此，我们在欧洲温带落叶林沿自然小气候、光照和大气候梯度安装的全因子实验中评估了下层植物群落对变暖和光照添加的功能响应。此外，我们将这些功能反应与物种的生活史综合征和热生态位相关联。
• 我们发现社区对变暖处理没有显着的反应。然而，光照处理对社区产生了更大的影响，这主要是由于快速定植的通才而不是缓慢定植的森林专家的反应。森林结构强烈介导了对光照的响应，并且对功能性状和总植物覆盖度也有明显的影响。
• 短期实验性变暖的影响很小，表明下层物种对气候变化的反应存在时间滞后。树冠干扰，例如由于干旱、害虫或伐木，具有强烈而直接的影响，特别有利于结构复杂森林下层的多面手。