| Grassland is the largest vegetation type in China’s terrestrial ecosystems,accounting for about 40%of the country’s land area.It plays an extremely important ecological role in maintaining biodiversity,retaining soil nutrients,and reducing soil erosion.The Nanshan grassland in Hunan Province is the largest plateau grassland in southern China and is a unique plant type in the region.Due to long-term human activities and the combined effects of global changes,soil nutrient loss in the area has been severe,seriously affecting grassland productivity.After the Nanshan grassland ecosystem was included in the Nanshan National Park management scope,protecting the integrity and authenticity of the Nanshan grassland ecosystem and improving grassland productivity have become the most important tasks.This study takes the existing artificial grassland,artificial shrub,natural grassland,and natural shrub in the Nanshan grassland ecosystem as research objects,and systematically.analyzes the differences in plant biomass and plant diversity,plant nutrients,soil nutrients and their ecological stoichiometry,and soil enzyme activity characteristics among different grassland types.The differences in aboveground and belowground ecological factors among different grassland types were compared,and the correlation between different grassland types and ecological factors was revealed.The research results provide theoretical basis and data support for the ecological restoration process of the Nanshan grassland ecosystem.The study results show that:(1)Characteristics of plant species diversity:A total of 64 species from 50 genera and 23 families were recorded in this study.Among them,Poaceae had 14 species from 12 genera,Rosaceae had 8 species from 4 genera,Asteraceae had 7 species from 6 genera,Fabaceae had 7 species from 4 genera,and Polygonaceae had 6 species from 3 genera,accounting for 21.88%,12.5%,10.93%,10.93%,and 7.7%of the total number of species,respectively,and a total of 65.63%and 58%of the total number of genera and species,respectively.Therefore,Poaceae,Rosaceae,Asteraceae,Fabaceae,and Polygonaceae occupy dominant positions in the plant species composition of the South Mountain ecosystem.The coverage,density,height,aboveground biomass,belowground biomass,species richness,Margalefs richness index,Shannon-Wiener diversity index,Simpson’s dominance index,and Pielou’s evenness index of different grassland types were found to be in the order of natural shrubland>natural grassland>artificial shrubland>artificial grassland.Characteristics of plant nutrients:The leaf carbon content in different grasslands in the study area showed the following trend:natural shrub grassland(344.79 g·kg-1)>natural grassland(300.18 g·kg-1)>artificial shrub grassland(288.39 g·kg-1)>artificial pasture(251.56 g·kg-1).The leaf nitrogen content in different grasslands showed the following trend:artificial shrub grassland(24.41 g·kg-1)>artificial pasture(22.01 g·kg-1)>natural grassland(18.52 g·kg-1)>natural shrub grassland(14.20 g·kg-1).The leaf phosphorus content in different grasslands showed the following trend:artificial shrub grassland(0.87 g·kg-1)>artificial pasture(0.70 g·kg-1)>natural grassland(0.67 g·kg-1)>natural shrub grassland(0.38g·kg-1).The average nitrogen to phosphorus ratio(N/P)in the leaves of the South Mountain grassland was 30.69,which is higher than the global average level of 15.55,indicating that the South Mountain grassland is more limited by phosphorus.Soil nutrient characteristics:The soil water content,SOC,TN,TP,TK,AK,AP,NH4+,and soil enzyme activity of the four different grassland types all showed an overall increasing trend,with the highest values observed in the natural shrubland,followed by natural grassland,artificial shrubland,and artificial pasture.In contrast,bulk density and pH showed a decreasing trend,with the highest values observed in the artificial pasture,followed by artificial shrubland,natural grassland,and natural shrubland.Soil ecological stoichiometry characteristics:The C/N ratios of soils from different grasslands ranged from 17.38 to 18.63,with the ranking of artificial pasture>natural grassland>natural shrub>artificial shrub.The C/P ratios of soils from different grasslands ranged from 46.22 to 117.77,with the ranking of artificial pasture>artificial shrub>natural shrub>natural grassland.The N/P ratios of soils from different grasslands ranged from 2.30 to 6.09,with the ranking of artificial pasture>artificial shrub>natural shrub>natural grassland.Influence of environmental factors on soil ecological stoichiometry:Based on RDA analysis,the main aboveground environmental factors influencing soil ecological stoichiometry of different grassland types are aboveground biomass,belowground biomass,and Shannon-Wiener index.The main belowground environmental factors are TK,soil urease,soil ammonium nitrogen,and soil moisture content. |
