The Effects Of Nitrogen Addition On Spatial Distribution Patterns Of The Plant Community In An Alpine Meadow

Nitrogen absorption and utilization can easily alter the spatial heterogeneity of vegetation, influencing ecosystem processes and biodiversity in natural grasslands. Understanding why and how nitrogen fertilizing changes species spatial distribution patterns is important for the preservation and restoration of biodiversity in grasslands. We use alpine meadows in the Qinghai-Tibetan Plateau to test the hypothesis that fertilizing alters plant diversity by changing inter- and intra- specific species distributions. Using recently developed spatial analyses combined with detailed aboveground ramet-mapping of entire plant communities(51 species) at different nitrogen addition Ievels(0g/m2,5g/m2,10g/m2,15g/m2),we show differences between fertilized and controlled areas that emerged at scales of just one meter. Species richness was similar at very small scales(0.0625 m2), but at larger scales diversity in fertilized areas fell about 94%(5g/m2)、 82%(10g/m2)、88%(15g/m2)of corresponding controlled areas. These differences were explained by differences in spatial distributions, In fertilized area and controlled area, given that there is no significant differences in total abundance and species richness. We found significant difference in species abundance within single functional groups. The composition of dominant species in fertilized area is also different from the control area. We conducted the point pattern analysis of intra- and interspecific associations within the functional groups. We found that fertilization enhanced inter- and intraspecific aggregations in the family of Poaceae, but caused decreased turnover in family of Gentianaceae and Ranunculaceae at fertilized area. At larger scales, reduced species turnover resulted in lower species richness.Our study provides strong support to the theoretical prediction that inter- and intra-specific aggregation produces local spatial patterns that scale-up to affect species diversity in a community. It also demonstrates that the impacts of fertilization can manifest through this mechanism, lowering diversity by reducing spatial turnover in species. Finally, it highlights the spatial distribution patterns of the plant community that are likely responding to fertilizing and thereby altering aggregation patterns, providing new insights for monitoring and mediating the impacts of fertilizing.