Effects Of Soil Nutrient Heterogeneity On Species Composition And Biomass Of An Alpine Meadow Community

The distribution of soil nutrients in horizontal space is heterogeneous rather than uniform.A large number of studies have shown that spatial heterogeneity of soil nutrients can significantly affect the growth,physiology,morphology,reproduction and biomass allocation of individual plants,and may change the intra-specific and inter-specific interactions of plants.Although there are also studies examining the effects of soil nutrient heterogeneity on species composition and biomass of plant communities,almost all of them have been carried out in the greenhouse for a relatively short period of time(usually within one growing season),and there is a lack of relevant long-term experiments in field.In this study,I examined long-term effects of soil nutrient heterogeneity on species composition and biomass of an alpine meadow community on the Tibetan plateau.In the field experiment,the basic nutrient addition level(N:3.000 g/m2,P:0.750 g/m2,K:2.986 g/m2)was set according to the concentrations of N,P and K in cow feces,and five different homogeneous nutrient treatments(0,0.5,1,1.5,and 2 times of the basic nutrient level)were set up to test the effects of homogeneous nutrient level on species composition and biomass of the alpine meadow.At the same time,six nutrient heterogeneity treatments with two levels of patch size(large patch and small patch)crossed with three levels of patch contrast(high contrast,low contrast and mixed contrast)were also established to test the effect of soil nutrient heterogeneity and patch scale and contrast on species composition and biomass of the alpine meadow.In the heterogeneous treatments,the total amount of nutrients applied to the plots was the same as that in the homogeneous treatment with 1 times of the basic nutrient level.In each year,nutrients were added to the plots in July,and plot survey and aboveground biomass harvest were conducted in August.Based on coverage data of each species,the Shannon-Wiener index,richness and evenness were calculated.After one growing season,it was found that the homogeneous addition of nutrients had significant effects on aboveground biomass of grasses and total aboveground biomass of the alpine meadow community.High nutrients significantly increased biomass of grasses and aboveground biomass of the alpine meadow community,but had no significant effects on biomass of other functional groups(sedges,forbs and legumes).Patch scale,patch contrast or their interaction had no significant effect on diversity or biomass of the communities and functional groups.After two growing seasons,soil nutrient homogeneity had no significant effect on Shannon-wiener index,richness or evenness.It also had no significant effect on total aboveground biomass of the communities,but had a significant impact on biomass of grasses.High nutrient addition significantly increased biomass of grasses.Patch scale,patch contrast or their interaction had no significant effect on diversity or biomass of the communities or functional groups.After three growing seasons,the homogeneous addition of soil nutrients had no significant effect on community biomass or diversity,but high nutrient levels significantly reduced biomass of legumes.Patch size had no significant effect on community biomass or species diversity,but patch contrast significantly affected biomass of grasses and species richness.Mixed patch contrast increased biomass of grasses and high patch contrast enhanced species richness.These results suggest that,in a relatively short time(three growing seasons),the high soil nutrient level was beneficial to biomass of grasses and tended to reduce biomass of legumes.In heterogeneous soil nutrient treatments,the mixed patch contrast increased biomass of grasses,and the high patch contrast improves species richness.Considering that environmental heterogeneity is crucial to understand how alpine ecosystems respond to climate change,the long-term effects of soil nutrient heterogeneity on species composition and biomass of communities in field need to be studied further.