Data from: Evidence for long-term shift in plant community composition under decadal experimental warming

Summary: 1. Long-term, slow ecological processes such as changes in plant community structure and composition strongly regulate ecosystem responses to climate change. Shifts in plant community are expected in chronically altered environments under warming. However, experimental evidence for long-term shifts and the associated mechanisms is still scarce in temperate grasslands. 2. Here, we explore the long-term responses of a prairie plant community to 14-year (2000-2013) manipulations of climate warming and clipping in Oklahoma, USA. Infrared heaters were used to elevate soil temperature by about 2 ºC all year round and annual clipping was applied to mimic hay harvest. 3. Community composition was resistant to experimental warming in the first seven years, but started to show responses starting from the eighth year; clipping consistently affected community composition over the years. Compositional change under long-term warming was mainly due to one invasive species and three dominant species. The negative correlations in relative abundance between the invasive species and the dominant species suggest inter-specific competition. Community structure (i.e., richness, evenness and diversity) had no overall response to experimental warming. However, in 2007, the extreme wet year, warming reduced species richness by 30%. Clipping promoted species richness by 10% on average over the 14 years but decreased community evenness. Warming did not interact with clipping in influencing the plant community variables. 4. Synthesis: Our study provides experimental evidence for long-term shifts in plant community composition due to warming and revealed novel mechanisms (i.e., species invasion and associated biotic interactions) underlying the long-term shift. The results also suggest that climate extremes may elicit or advance community responses to climate warming. The findings highlight that long-term climate change experiments are essential to reveal potential shifts in community composition.

摘要：1. 长期缓慢的生态过程（ecological processes），如植物群落结构与组成的变化，可强烈调控生态系统对气候变化的响应。在长期受气候变暖干扰的生境中，植物群落预计将发生显著变化。然而，温带草原（temperate grasslands）中关于此类长期群落变化及其相关机制的实验证据仍较为匮乏。2. 本研究以美国俄克拉荷马州的一处北美草原（prairie）植物群落为研究对象，探究其在2000-2013年为期14年的气候变暖与刈割（clipping）操控实验下的长期响应。实验采用红外加热器（infrared heaters）全年将土壤温度提升约2℃，并通过年度刈割模拟干草收获作业。3. 实验前7年，群落组成对实验性气候变暖表现出抗性，但从第8年起开始出现响应；而刈割处理在整个实验周期内始终对群落组成产生显著影响。长期变暖下的群落组成变化主要由1种入侵物种（invasive species）与3种优势物种（dominant species）驱动。入侵物种与优势物种的相对多度（relative abundance）呈负相关，这提示存在种间竞争（inter-specific competition）。群落结构（即物种丰富度、均匀度与多样性）整体上未对实验性变暖产生响应。但在2007年这一极端湿润年份，变暖处理使物种丰富度降低了30%。刈割处理在14年实验周期内平均提升了10%的物种丰富度，却降低了群落均匀度。变暖与刈割处理在影响植物群落变量方面未表现出交互效应。4. 综合结论：本研究提供了气候变暖导致植物群落组成发生长期变化的实验证据，并揭示了长期变化背后的新型机制，即物种入侵与相关生物相互作用（biotic interactions）。研究结果还表明，极端气候事件（climate extremes）可能诱发或加速群落对气候变暖的响应。本研究结果凸显了长期气候变化实验对于揭示群落组成潜在变化的重要性。