Spatial assembly of grassland communities and interrelationships with productivity

1. 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. 2. Here, species segregation index (Ms-com) 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 m(2) 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 Ms-com and interrelationships with above-ground net primary productivity (ANPP). 3. 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 Ms-com 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 Ms-com on ANPP is stronger than that of species and phylogenetic diversity. 4. 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.

Automated summary

This study investigated plant communities from three different plateaus and found that grassland communities tend to form intraspecific aggregations, which are more apparent in regions with low annual precipitation. The strong intraspecific aggregation on the Loess Plateau was mainly due to low sexual reproduction allocation, while on the Mongolian Plateau, reproductive allocation and the interactive effect of annual precipitation and species richness were the dominant factors. On the Tibetan Plateau, low species richness and the interactive effect of annual precipitation and species richness were the main reasons for increased intraspecific aggregation. Furthermore, the independent influence of species segregation index on above-ground net primary productivity was stronger than that of species and phylogenetic diversity on all three plateaus.