Nutrients Stoichiometry Of Soil And Plant At Different Vegetation Degradation Stages In Northern Greater Xing’an Mountains

Greater Xing’an Mountains is one of important forestry base in China. However, under frequent fires and excessive logging, there is serious vegetation degradation in Greater Xing’an Mountains. The objective of this study was to determine the impact of vegetation degradation on nutrient concentrations and stoichiometry of soil and plant. Different vegetation degradation stages in aridity sunny-slope of Greater Xing’an Mountains were sampled, and different vegetation degradation stages were respectively Quercus mongolica forest, shrub, shrub-grass, and grassland. Nutrient concentrations and stoichiometry of soil and plant, and species diversity of plant community at different vegetation degradation stages were researched. The results showed:1. Soil nutrient concentrations decreased with vegetation degradation, while soil C, N, P stoichiometry increased. With vegetation degradation, soil total C concentration was shrub> Quercus mongolica forest> shrub-grass> grassland; soil total N, total P, available P, total K and available K concentrations were Quercus mongolica forest> shrub> shrub-grass> grassland; soil NH4+-N and NO3--N concentrations were Quercus mongolica forest> shrub> grassland> shrub-grass. With vegetation degradation, soil C:N ratio gradually increased, and soil C:N ratio in Quercus mongolica forest was significantly lower than shrub, shrub-grass, grassland (P<0.05);0-10cm soil C:P ratio gradually increased, while10～20cm soil C:P ratio increased after the first drop, and10～20cm soil C:P ratio in grassland was significantly higher than shrub-grass, shrub (P<0.05); soil N:P ratio decreased first and then increased, and soil N:P ratio in grassland was significantly higher than shrub-grass, shrub (P<0.05).2. Vegetation degradation remarkably effected leaf C, N, P concentrations and stoichiometry of plant community. With vegetation degradation, leaf C concentration of plant community was shrub> Quercus mongolica forest> shrub-grass> grassland, and the average range was439.42～464.71g/kg; leaf N, P concentration decreased with vegetation degradation, and the average ranges were respectively16.25～21.66g/kg,1.22～2.99g/kg; C:N, C:P and N:P ratios of plant community were Quercus mongolica forest> shrub> shrub-grass> grassland, and the average ranges were respectively21.27～27.14,155.52～368.15,7.35～13.61. The leaf N concentration and P concentration of plant community respectively had very significant positive correlation with0-10cm soil total N and total P (P<0.01), while had no significant correlation with10～20cm soil total N and total P (P>0.05).3. The leaf N:P ratios of all common species in Quercus mongolica forest and shrub were below14, while the leaf N:P ratios of8common species in shrub-grass were below14, one was14～16, and the leaf N:P ratios of7common species in grassland were below14, the other two were above16. These results suggest that the vegetation growth at different vegetation degradation stages in Greater Xing’an Mountains is generally N-limited.4. Nutrient concentrations and stoichiometry of soil at different vegetation degradation stages abivously affected the species diversity of plant community, while the species diversity of plant community had some impact on nutrient concentrations and stoichiometry of plant community. Species richness, Simpson index, Shannon index, evenness index had significant correlation with soil available nutrients concentrations (P<0.05), while had no significant correlation with soil total nutrients concentrations, stoichiometry (P>0.05). Species richness, Simpson index, Shannon index, evenness index had significant correlation with leaf C, N, P, concentrations of plant community (P<0.05), while had no significant correlation with leaf C:N, C:P, N:P ratios (P>0.05).