Spatial assembly of grassland communities and interrelationships with productivity

Knowledge on the fine‐scale spatial aggregation is pertinent for deciphering plant community dynamics, as interactions among sessile plants mainly occur in the neighbourhood. However, the spatial assemblage mechanism and interrelationships with productivity remain poorly understood. Here, species segregation index (Mscom) was used to quantify the interspecific segregation (or intraspecific aggregation) of the neighbourhood in plant communities from three contrasting plateaus. We employed the coordinates for 125,726 individual plants (within 1 m2 plots) sampled in natural grassland communities across two temperate grasslands (Loess Plateau and Mongolian Plateau) and one alpine grassland (Tibetan Plateau) to elucidate the assembly mechanisms of Mscom and interrelationships with above‐ground net primary productivity (ANPP). We found that these grassland communities tended to assemble into intraspecific aggregations; the phenomenon was more apparent in regions with low annual precipitation. In grassland communities on Loess Plateau, the strong intraspecific aggregation was mainly due to low sexual reproduction allocation; on Mongolian Plateau, reproductive allocation was also the dominant factor for Mscom variation, followed by the interactive effect of annual precipitation and species richness, whereas on Tibetan Plateau, low species richness was the main reason for increased intraspecific aggregation, followed by the interactive effect of annual precipitation and species richness, and reproductive allocation. More importantly, on all three plateaus, the independent influence of Mscom on ANPP is stronger than that of species and phylogenetic diversity. We elucidated the potential mechanisms shaping spatial aggregation in grassland communities at large scale, and emphasize the critical role of spatial aggregation in predicting the variation of ANPP. Read the free Plain Language Summary for this article on the Journal blog. 摘要 植物个体的邻域空间结构对于理解群落动态十分重要，因为对固着植物而言其相互作用主要发生在邻域尺度。然而，目前对邻域空间结构的构建机制以及其与生产力的关系仍然知之甚少。 本研究中，采用物种隔离指数(Mscom)来量化草地群落邻域尺度的种间隔离(或种内聚集)。我们基于2个温带草原(黄土高原和蒙古高原)和1个高寒草原(青藏高原)上125,726株植物在1m2样方内的相对位置坐标，阐明了Mscom的构建机制以及其与地上净初级生产力(ANPP)的关系。 我们发现，这些草地群落倾向于种内聚集，而且这种现象在年降水量低的地区更为明显。在黄土高原上，种内聚集现象主要来源于低的有性繁殖分配策略；在蒙古高原，繁殖分配也是Mscom空间变异的主导因素，其次是年降水和物种丰富度的交互效应；而在青藏高原，较低的物种丰富度是导致种内聚集的主要原因，其次是年降水和物种丰富度的交互效应，然后是繁殖分配。更为重要的是，在三个高原上，Mscom对ANPP空间变异的独立影响明显强于物种和系统发育多样性。 我们阐明了大尺度上草地群落邻域空间聚集的潜在机制，并强调其在预测ANPP变异中的关键作用。 Read the free Plain Language Summary for this article on th