Data from: Light accelerates plant responses to warming

Competition for light has profound effects on plant performance in virtually all terrestrial ecosystems. Nowhere is this more evident than in forests, where trees create environmental heterogeneity that shapes the dynamics of forest-floor communities1,​2,​3. Observational evidence suggests that biotic responses to both anthropogenic global warming and nitrogen pollution may be attenuated by the shading effects of trees and shrubs4,​5,​6,​7,​8,​9. Here we show experimentally that tree shade is slowing down changes in below-canopy communities due to warming. We manipulated levels of photosynthetically active radiation, temperature and nitrogen, alone and in combination, in a temperate forest understorey over a 3-year period, and monitored the composition of the understorey community. Light addition, but not nitrogen enrichment, accelerated directional plant community responses to warming, increasing the dominance of warmth-preferring taxa over cold-tolerant plants (a process described as thermophilization6,10,​11,​12). Tall, competitive plants took greatest advantage of the combination of elevated temperature and light. Warming of the forest floor did not result in strong community thermophilization unless light was also increased. Our findings suggest that the maintenance of locally closed canopy conditions could reduce, at least temporarily, warming-induced changes in forest floor plant communities.

光照竞争对几乎所有陆地生态系统中的植物表现均具有深远影响。这一点在森林中体现得尤为显著：林木可营造环境异质性，进而塑造林下群落的动态1,2,3。观测证据表明，生物对人为全球变暖与氮污染的响应，可能会因乔灌木的遮阴效应而减弱4,5,6,7,8,9。本研究通过实验证实，林木遮阴会减缓冠层下方群落因变暖而发生的变化。我们在为期3年的研究中，对温带森林林下的光合有效辐射（photosynthetically active radiation）、温度与氮素水平进行了单因素及交互组合调控，并监测了林下群落的组成结构。光照添加而非氮素富集，可加快植物群落对变暖的定向响应，使喜温类群相较于耐寒植物占据优势——这一过程被称为热趋同（thermophilization）6,10,11,12。高大的竞争性植物能最大限度利用增温与光照增强的协同效应。若未同步提升光照水平，林地升温并不会引发显著的群落热趋同现象。本研究结果表明，维持局部闭合冠层的环境条件，至少可在短期内减缓变暖驱动的林下植物群落变化。