Yue et al.zip

It has been widely reported that appropriate grazing can promotes grassland biodiversity and productivity, thereby ensuring rangeland sustainability. Yet, experimental testing of the grazing advantage is still rare, especially considering how little we know about the underlying mechanisms. We hypothesized that appropriate grazing can promote biomass production in a plant community through increasing resource acquisition and/or utilization by extending functional trait space of the plant community.To test this hypothesis, we conducted a grazing experiment (i.e., control = no grazing, light, moderate, and heavy grazing) in Tibetan alpine meadows. We measured 13 functional traits in each plot for each of the 22 species commonly occurred in all plots to quantify the functional trait space of the plant community, and to identify which species positively (i.e., grazing increasers), negatively (i.e., decreasers), or insignificantly (i.e., generalists) responds to grazing in term of changes in species relative abundance.Comparing to control, the biomass production was significantly increased in all three grazed treatments, while the moderate and heavy grazing also significantly increased functional trait space of the plant community. Across plots, the increase in biomass production was significantly associated with the extension of functional trait space. The grazing-induced extensions of trait space were likely attributed to an increase leaf trait variation of composing species to enhance photosynthesis, especially on sedges and legumes and for grazers increasers and generalists.The study not only provides robust evidence for the advantage of appropriate grazing, but it also provides the first evidence to unveil a mechanistic linkage from trait variation and species performance to community functional space and productivity in response to grazing. Hence the study offers a new insight into understanding the functional space mediated linkages from grazing-induced plant response upon dynamics of grassland function.

已有大量研究表明，适度放牧可提升草地生物多样性与生产力，进而保障牧场可持续性。然而，针对放牧优势的实验验证仍较为匮乏，尤其是在我们对其潜在机制认知尚且不足的背景下。本研究提出假说：适度放牧可通过拓展植物群落的功能性状空间（functional trait space），提升资源获取与/或利用效率，进而促进植物群落的生物量生产。为验证该假说，我们在青藏高原高寒草甸开展了放牧实验，设置了4组处理：对照组（无放牧）、轻度放牧、中度放牧与重度放牧。我们针对所有样地中均常见的22个物种，在每个样地内测定了13项功能性状，以此量化植物群落的功能性状空间，并依据物种相对多度的变化，甄别出对放牧呈正向响应的物种（即放牧增加种）、负向响应的物种（即放牧减少种）以及响应不显著的物种（即泛化种）。与对照组相比，三个放牧处理组的生物量生产均显著提升；其中中度放牧与重度放牧还显著拓展了植物群落的功能性状空间。在所有样地中，生物量生产的提升与功能性状空间的拓展呈显著正相关。放牧诱导的性状空间拓展，可能源于组成群落的物种叶片性状变异增加，从而提升光合效率，这一现象在莎草科、豆科植物以及放牧增加种和泛化种中尤为明显。本研究不仅为适度放牧的优势提供了坚实证据，同时首次揭示了一条机制性关联链条——即性状变异与物种表现，如何通过放牧响应，作用于群落功能性状空间与生产力。因此，本研究为理解由功能性状空间介导的、放牧诱导的植物响应与草地功能动态之间的关联提供了全新视角。