Grazing disturbance plays a crucial role in regulating plant community structure and ecosystem function in drylands. However, few studies show that how grazing disturbance affects the relationships between functional traits and aboveground plant biomass (AGB). Here, we presented a comparative result from grazing experiment with three levels of grazing intensities (no grazing, moderate and heavy grazing) between shrub- and grass-dominated community in desert steppe, Inner Mongolia. We measured vegetation characteristics and plant traits (plant height, LT: leaf thickness, SLA: specific leaf area, LDMC: leaf dry matter content, LCC: leaf carbon content and LNC: leaf nitrogen content) in the two communities across 2 years (2017–2018). We used the linear regression analysis and the structural equation modeling (SEM) to examine how grazing affect the associations of AGB with plant traits. We found that grazing decreased vegetation cover, AGB and litter mass in two communities, and caused the differences in AGB among two communities. Heavy grazing eliminated the associations of AGB with SLA and LCC in shrub community, while led to their positive or negative associations in grass community. The SEM showed that grazing indirectly decreased AGB through its effect on LT in shrub community, and its effect on plant height in grass community. These results suggest that changes in leaf traits induced by heavy grazing can explain AGB in grass- rather than shrub-community, thereby possibly contributing to AGB differences between two communities. Indirect effects of increased grazing intensities on AGB in shrub or grass community are dependent on specific functional traits.

中文翻译：

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放牧强度增加导致沙漠草原灌木和草主导群落功能性状与地上植物生物量之间关系的分化

放牧干扰在调节旱地植物群落结构和生态系统功能方面起着至关重要的作用。然而，很少有研究表明放牧干扰如何影响功能性状与地上植物生物量（AGB）之间的关系。在这里，我们展示了内蒙古沙漠草原以灌木和草为主的群落之间三个放牧强度（无放牧、中度和重度放牧）的放牧实验的比较结果。我们测量了两个社区在 2 年（2017 年）的植被特征和植物性状（植物高度，LT：叶片厚度，SLA：比叶面积，LDMC：叶片干物质含量，LCC：叶片碳含量和 LNC：叶片氮含量） –2018）。我们使用线性回归分析和结构方程模型 (SEM) 来检查放牧如何影响 AGB 与植物性状的关联。我们发现放牧降低了两个社区的植被覆盖度、AGB 和凋落物质量，并导致了两个社区之间 AGB 的差异。重度放牧消除了灌木群落中 AGB 与 SLA 和 LCC 的关联，而导致它们在草群落中的正负关联。SEM表明，放牧通过对灌木群落LT和草群落株高的影响间接降低了AGB。这些结果表明，重度放牧引起的叶片性状变化可以解释草群落而不是灌木群落中的 AGB，从而可能导致两个群落之间的 AGB 差异。