Abstract：
Snowpack is closely related to vegetation green-up in water-limited ecosystems, and has effects on growing-season ecosystem processes. However, we know little about how changes in snowpack depth and melting timing affect primary productivity and plant community structure during the growing season. Here, we conducted a four-year snow manipulation experiment exploring how snow addition, snowmelt delay and their combination affect aboveground net primary productivity (ANPP), species diversity, community composition and plant reproductive phenology in seasonally snow-covered temperate grassland in northern China. Snow addition alone increased soil moisture and nutrient availability during early spring, while did not change plant community structure and ANPP. Instead, snowmelt delay alone postponed plant reproductive phenology, and increased ANPP, decreased species diversity and altered species composition. Grasses are more sensitive to changes in snowmelt timing than forbs, and early-flowering forbs showed a higher sensitivity compared to late-flowering forbs. The effect of snowmelt delay on ANPP and species diversity was offset by snow addition, probably because the added snow unnecessarily lengthens the snow-covering duration. The disparate effects of changes in snowpack depth and snowmelt timing necessitate their discrimination for more mechanistic understanding on the effects of snowpack changes on ecosystems. Our study suggests that it is essential to incorporate non-growing-season climate change events (in particular, snowfall and snowpack changes) to comprehensively disclose the effects of climate change on community structure and ecosystem functions.
摘要：
在水资源有限的生态系统中，积雪与植被绿化密切相关，并对生长季节生态系统过程产生影响。然而,我们对积雪深度和融化时间的变化如何影响生长季节的初级生产力和植物群落结构知之甚少。这里,我们进行了为期四年的雪操纵实验，融雪延迟及其组合影响地上净初级生产力(ANPP)，物种多样性,中国北方季节性积雪温带草地的群落组成和植物繁殖物候。在早春期间，仅添加雪就增加了土壤水分和养分利用率，而没有改变植物群落结构和ANPP。相反，仅融雪延迟就推迟了植物的繁殖物候，增加ANPP，物种多样性下降，物种组成改变。草对融雪时间的变化比forbs更敏感，与晚开花forbs相比，早开花forbs表现出更高的敏感性。融雪延迟对ANPP和物种多样性的影响被雪的添加所抵消，可能是因为增加的雪不必要地延长了积雪的持续时间。积雪深度和融雪时间变化的不同影响要求对积雪变化对生态系统的影响进行更多的机械理解。我们的研究表明，将非生长季节的气候变化事件（特别是，降雪和积雪变化），以全面揭示气候变化对群落结构和生态系统功能的影响。
