Plant Diversity And Its Relation To Soil Resources Heterogeneity In Different Grassland Types From Northern China

As the important feature of the ecosystem,plant diversity plays an important role in maintaining ecosystem productivity,stability,sustainability and other aspects.Scientists have attempted to reveal the maintaining mechanism of plant diversity from different perspectives.Spatial heterogeneity of environmental resources is considered one of the most important factors governing plant species diversity.As one of the principal concepts,heterogeneity-diversity hypothesis holds that heterogeneous environments should support more species than homogeneous environments,and it is widely assumed that there is a positive heterogeneity-diversity relationship(HDR).The premise of positive HDR is based on classical niche theory,which expects species specialize on particular resource regimes,and only live in certain environmental conditions,and different species occupy different ecological niches.Hence,habitat heterogeneity allows more species co-existence.The relationship between spatial environmental heterogeneity and species diversity has been checked in many ecosystems.However,it has never been tested with field surveys and experimental works in northern China.In this study,four major grassland types(meadow steppe,typical steppe,desert steppe,alpine meadow)in northern China were chosen as the research objects.With the nested sampling design,we tested the plant diversity and spatial heterogeneity(coefficient of variation)of limiting soil resources(nitrogen availability)under different grassland types.And checking the correlation between spatial heterogeneity of soil nitrogen availability and plant diversity under different spatial scales(0.5 m×0.5 m,2.5 m×2.5 m,5 m×5 m,10 m×10 m,15 m×15 m)both in the local scales(within the different types of grassland)and regional scales(spanning four types of grassland steppe zone of northern China)respectively.We obtained the following main research results:(1)There was significant difference in plant diversity among the four major grassland types in northern China.Meadow steppe has the highest species richness at the plot scale(15m × 15 m)with 47 species,while 7 species at quadrat scale(0.5 m×0.5 m).Alpine meadow has the highest species richness at quadrat scale with an average of 22 species,while 33 species at the plot scale.Desert steppe has 27 species at plot scale and 7 species at quadrat scale.Typical steppe has the lowest species richness with 33 species at the plot scale and only3 at quadrat scale.(2)The spatial heterogeneity of soil nitrogen availability are all strong within four major grassland types in northern China,and the coefficients of variation are more than 30%,which presents on all spatial scales.There were significant differences in spatial heterogeneity of soil inorganic nitrogen availability among the different grassland types,showing that the highestheterogeneity of soil nitrogen availability was presented in the meadow steppe,and there was no significant difference among the other three grassland types.(3)For the analysis of the heterogeneity-diversity relationship within the local scale,we found there were significant correlations between spatial heterogeneity of soil nitrogen availability and species richness in both desert steppe and typical steppe,respectively,in 2.5m × 2.5 m scale and 10 m × 10 m scale.However,there were no significant correlations between spatial heterogeneity of soil nitrogen availability and species richness in either meadow steppe or alpine meadow from 0.5 m × 0.5 m scale to 15 m × 15 m of scale.(4)For the analysis of the heterogeneity-diversity relationship within the region scale,we found significant positive correlations between spatial heterogeneity of soil nitrogen availability and species richness in 15 m × 15 m scale.It demonstrated the important role of soil resource heterogeneity on maintaining plant diversity in regional scale and supported the heterogeneity-diversity hypothesis.Based on the above outcomes,we found the heterogeneity-diversity hypothesis occurs mainly in the larger regional context,which can be used as one of important factors in the distribution of species diversity among different grassland types in regional scale.While within a local scale,the establishment of heterogeneity-diversity hypothesis is uncertain,it may rely on different grassland types.Besides,the correlation between resource heterogeneity and plant diversity is strongly depended on the spatial scale regardless in local scale or regional scale,which further proves the importance of spatial scale.This study,not only contributes to full understanding of the basic characteristics of the plant diversity and the heterogeneity of soil resources,but also improves the further understanding of the mechanisms of formation and maintenance of plant diversity in the main grassland types in northern China.In addition,the study also provides an important data base for testing the heterogeneity-diversity hypothesis.