Research Of The Dominant Plants And Soil C,N,P Ecologic Stoichiometry Characteristics On The Grassland From Cultivated Land In A Typical Steppe In Ningxia

Ecological stoichiometry is a new direction in biochemistry and soil chemistry research.This method was applied to the cultivated grassland in typical steppe area of southern Ningxia,using a spatial gradient instead of a temporal gradient.The ecological stoichiometry characteristics of dominant plant and soil C,N,P of cropland restored to grassland in 1995,2000,2005,2007,2011,2013,2014,and 2016,were analyzed to explore the influence of dominant plants and soil C,N,P ecological stoichiometry on vegetation succession.The main conclusions are as follows:(1)There were 24 species in the plots belonging to eight families and 20 genera.Species richness and diversity index showed a decreasing trend and increases with increasing recovery duration.The community succession kept positive and stable,through the self adjustment and selection process of the ecological system.Combined the species composition,dynamic change characteristics of community diversity indices and TWINSPAN classification results,which divided the natural vegetation succession sequence into three main stages:Artemisia scoparia and Leymus secalinus stage(restored less than 3 years),Leymus secalinus and Artemisia scoparia stage(restored for 5?11 years),and Stipa bangeana and Leymus secalinus stage(restored for 16?21 years).This reflects the trend of succession of community vegetation types from annual to perennial vegetation.(2)Aboveground portions of dominant plants had C,N,P content that was greater than the belowground nutrient content.The content of organic carbon with aboveground portion of the dominant plants varied from 55.09 to 63.77%,and the average value(± SD)was 55.31 ±4.25%;the total nitrogen content in 0.37?0.80%,the average value(± SD)was 0.55 ± 0.18%;the total phosphorus content in 0.09-0.35%,the average value(± SD)was 0.15 ± 0.07%.The organic carbon content of the dominant plants increased with increasing restoration years(P<0.05).The content of organic carbon in the aboveground portion of the dominant plants gradually increased from May to September.C:N was low in May,and relatively high in August.C:P and N:P reached the lowest value of the year in September.(3)Community organic carbon content decreased with increasing restoration years,and there were significant differences among different years(P<0.05).C:N,C:P,N:P increased with the increase of restoration years.The C:N of communities was maximum in July and August(P<0.05).C:P and N:P was highest in June(P<0.05).The content of organic carbon in the litter of communities decreased with restoration years.The total N and P increased first and then decreased with restoration years.(4)Soil nutrient(organic carbon,total nitrogen,total phosphorus,available nitrogen,available phosphorus,available potassium)level decreased with the soil depth.Soil C:N decreased gradually from 1995 to 2014 restoration years(restored for 2-21 years).C:N of the wheat field(restored for 0 years)was smaller than the grassland restored from cultivated land in 2013 and 2014(restored less than 3 years),and larger than other land which returned to grassland for more than 5 years.The content of soil nutrients changed little with the seasons.(5)Dominant plant N:P was less than 14,which suggests that dominant plant growth was mainly limited by N.That the correlation between ecological stoichiometry characteristics of dominant plants and soil was not significant,showed that the change of soil ecological stoichiometry was not the main driving factor of vegetation succession in these restored grasslands.