高寒草灌植被类型对不同坡位土壤碳氮磷化学计量特征的影响OA

The alpine meadow on the Qinghai-Tibet Plateau plays a crucial role in forage production,carbon sequestration,and nutrient and water cycling.However,under the combined effects of climate warming and overgrazing,the exacerbating shrub encroachment of the alpine meadows has led to vegetation community succession,which in turn constrains the sustainable development of alpine grassland livestock husbandry.Slope aspect and position are key topographic factors influencing vegetation types,soil nutrient balance,and spatial distribution at the hillslope.Nevertheless,the intrinsic mechanisms by which slope position and grass-shrub vegetation types synergistically regulate the spatial patterns of plant communities and soil nutrients remain to be elucidated.This study was conducted on a typical hillslope in the Zoige Plateau,selecting different slope positions and vegetation types to reveal the interactive relationships between plant community characteristics and soil nutrients through field community surveys,topsoil(0-10 cm)sampling,and analytical testing.The results showed that the grassland plant community characteristics within grass-shrub patches exhibited significant variation along the slope position.At the upper and middle slope positions,total cover,biomass,and diversity were higher in the grass-shrub patches,whereas the grassland patches had higher species richness.Within the grass-shrub patches,total cover,biomass,and diversity at the upper and middle positions were higher than at the lower position,where total cover and biomass decreased by 37％and 131％,respectively,compared to the maximum values at the middle position.In addition,the grassland patches showed the highest species richness at the lower slope position.This pattern reflects a"fertility island effect",where organic matter and nutrients were enriched at the middle and upper positions within grass-shrub patches,and the organic matter content at the lower position was 29％and 60％lower than at the upper and middle positions,respectively.Conversely,the grassland patches exhibited nutrient enrichment at the lower slope position.The N:P ratio was significantly lower in grass-shrub patches than in grassland patches,while their C:P and C:N ratios decreased down the slope,with C:P decreasing by 78％.In grass-shrub patches,nutrient cycling was significantly correlated with plant community diversity(P<0.05),and soil carbon,nitrogen,and phosphorus stocks and their stoichiometric characteristics were co-regulated by soil organic matter,bulk density,and nitrogen.Consequently,by revealing the co-regulation of soil carbon,nitrogen,and phosphorus stocks and stoichiometry by shrub encroachment and slope position in alpine grasslands,this study provides a scientific basis for the management of alpine shrub-encroached grasslands.