Responses of Plant Community Composition and Biomass Production to Warming and Nitrogen Deposition in a Temperate Meadow Ecosystem

Climate change has profound influences on plant community composition and ecosystem functions. However, its effects on plant community composition and biomass production are not well understood. A four-year field experiment was conducted to examine the effects of warming, nitrogen (N) addition, and their interactions on plant community composition and biomass production in a temperate meadow ecosystem in northeast China. Experimental warming had no significant effect on plant species richness, evenness, and diversity, while N addition highly reduced the species richness and diversity. Warming tended to reduce the importance value of graminoid species but increased the value of forbs, while N addition had the opposite effect. Warming tended to increase the belowground biomass, but had an opposite tendency to decrease the aboveground biomass. The influences of warming on aboveground production were dependent upon precipitation. Experimental warming had little effect on aboveground biomass in the years with higher precipitation, but significantly suppressed aboveground biomass in dry years. Our results suggest that warming had indirect effects on plant production via its effect on the water availability. Nitrogen addition significantly increased above- and below-ground production, suggesting that N is one of the most important limiting factors determining plant productivity in the studied meadow steppe. Significant interactive effects of warming plus N addition on belowground biomass were also detected. Our observations revealed that environmental changes (warming and N deposition) play significant roles in regulating plant community composition and biomass production in temperate meadow steppe ecosystem in northeast China.气候变化对植物群落组成与生态系统功能具有深远影响。然而，其对植物群落组成及生物量生产的影响尚未得到充分阐释。本研究在中国东北温带草甸生态系统开展了为期四年的野外控制实验，旨在探究增温、氮（N）添加及其交互作用对植物群落组成与生物量生产的影响。实验性增温对植物物种丰富度、均匀度及多样性无显著影响，而氮添加则显著降低了物种丰富度与多样性。增温倾向于降低禾草类植物的重要值，却提升了杂类草的重要值，而氮添加则呈现相反的效应。增温倾向于提升地下生物量，但对地上生物量则表现出降低趋势。增温对地上生物量生产的影响依赖于降水条件：在降水较多的年份，实验性增温对地上生物量无显著影响，但在干旱年份则会显著抑制地上生物量。研究结果表明，增温通过改变水分可利用性，对植物生产产生间接影响。氮添加显著提升了地上与地下生物量生产，表明氮是调控研究区草甸草原植物生产力的关键限制因子之一。本研究还检测到增温与氮添加的交互作用对地下生物量存在显著影响。本研究结果显示，环境变化（增温与氮沉降）对中国东北温带草甸草原的植物群落组成与生物量生产具有显著调控作用。