Spatial assemblage of grassland communities and interrelationships with productivity

Knowledge on the fine-scale spatial structure is very important for
understanding plant community dynamics, as interactions among sessile
plants mainly occur in the neighborhood. 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
neighborhood 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 Loess Plateau (LP),
Mongolian Plateau (MP), and Tibetan Plateau (TP) 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 in intraspecific aggregations; the phenomena were more apparent
in desert grassland communities. Apart from the controls of
self-organization, climatic heterogeneity also plays an important role in
determining Mscom. In grassland communities on LP and MP, Mscom was
predominantly affected by reproductive allocation (RA); whereas on TP,
Mscom was more responsive and sensitive to climatic heterogeneity
(especially precipitation and low temperatures). We also found that Mscom
better explained the overall variations in ANPP than species diversity,
and mediated the response of ANPP to environmental variations; Mscom and
environmental effects jointly explained 22.7, 19.1, and 49.8% of the
variations in ANPP on LP, MP, and TP, respectively. Our findings provide
new insights into the underlying mechanisms of spatial assemblage of
grassland communities, and emphasize the critical role of spatial
structure in predicting the impacts of environmental change.