Distribution Characteristics Of Soil Carbon,Nitrogen And Phosphorus Contents With Slopes In Seasonal Pasture In Gannan,China

Soil is the core component of the alpine grassland ecosystem,the main site for the life activities of alpine grassland and an important hub for nutrient transformation,and it controls the nutrient cycle and effectiveness of the grassland ecosystem.As indicators for evaluating grassland soil quality and grassland health,soil organic carbon（SOC）,total nitrogen（STN）,and total phosphorus（STP）have a direct impact on grassland soil fertility and grassland productivity.Carbon-phosphorus ratio（C:P）,and nitrogen-phosphorus ratio（N:P）can reflect the changes in the proportion of soil nutrients in the alpine grassland,and indirectly indicate the abundance and deficiency of a certain element in the grassland.Understanding the distribution of soil nutrients in alpine grassland and its main influencing factors has far-reaching significance for the sustainable and healthy development of pastoral grasslands.In this paper,Maqu County on the eastern edge of the Qinghai-Tibet Plateau was taken as the research area,and the slope aspect was the main terrain factor to study and discuss the soil organic carbon,soil organic carbon,The spatial distribution of total nitrogen and total phosphorus content,density,and stoichiometric ratio characteristics and changes in vegetation community characteristics,and combined with correlation analysis to analyze the environmental factors that affect the spatial distribution of soil carbon,nitrogen,and phosphorus.A comparative study of summer and winter pastures was conducted.The main results are as follows:（1）The contents and densities of SOC,STN and STP changed significantly in different slopes between summer and winter pastures.The average contents of SOC,STN and STP in the 0-60 cm soil layers with different slope aspects of the pasture in summer were between 9.41-47.69 g/kg,2.5-5.83 g/kg,0.43-0.72 g/kg,and the soil organic carbon density（SOCD）,soil total nitrogen density（STND）,and soil total phosphorus density（STPD）averaged between 0.87-5.05 kg/m²,0.26-0.61 kg/m²,and0.039-0.071 kg/m².The average contents of SOC,STN and STP in the 0-60 cm soil layers with different slopes in winter pastures were 16.33-60.73 g/kg,2.65-5.62 g/kg,0.47-0.81 g/kg,and the average values of SOCD,STND and STPD were Between1.22-6.86 kg/m²,0.24-0.55 kg/m²,0.041-0.077 kg/m².（2）From the perspective of vertical distribution,the SOC content of different slope aspects of summer and winter pasture showed a significant downward trend with soil depth,and the vertical distribution trend of STN and STP content was basically consistent with SOC content.Soil organic carbon density（SOCD）,soil total nitrogen density（STND）and soil total phosphorus density（STPD）in the 0-60 cm soil layer of summer pasture and winter pasture were all 0-10 cm>10-20 cm>20-40 cm>40-60 cm,showing a significant downward trend with soil depth.From the aspect gradient,the SOC,STN and STP contents of the five aspects of the summer and winter pasture showed similar distribution patterns,and the content decline rateγ_SOC>γ_STN>γ_STP;The content of SOC,STN and STP in winter pastures are the highest in the north slope and the lowest in the south slope,and the content changes basically It follows an increase from the south slope to the north slope,and the content decline rate is consistent with the summer pasture.（3）Comparing the content and density of SOC,STN and STP in the 0-60 cm soil layer in summer and winter pastures,it is found that the SOC content of winter pastures is significantly higher than that of summer pastures;the STP content of winter pastures is slightly higher than that of summer pastures,and the difference is not significant;STN There was basically no difference in content,and the overall content was similar;the SOCD of winter pasture was slightly higher than that of summer pasture,the STPD of summer pasture was not significantly different from that of winter pasture,but the STND of summer pasture was higher than that of winter pasture,showing the opposite trend.（4）The number of species,coverage,aboveground biomass,and species diversity index on the southern slope of the pasture in summer were smaller than those on the northern slope.The number of species and species diversity index of summer pastures are generally larger than those of winter pastures,the number of species is significantly different,and the degree of reduction between the three indices of species diversity is also greater;In terms of coverage and aboveground biomass,the overall winter pastures are higher than summer pastures.（5）The range of C:N,C:P,N:P is 3.05-9.12,21.89-72.15,5.81-8.08 in different slope aspects of pasture in summer,and the depth of 0-60 cm in soil layer in winter pasture is 0-60 cm.C:N,C:P,N:P range is 6.34-11.93,34.38-76.15,6.33-7.52.The C:N and C:P of winter pastures were larger than those of summer pastures,and the N:P was smaller than that of summer pastures.In summer pasture surface soil C:N is lower,the decomposition of soil organic matter is faster,which makes organic nitrogen easier to mineralize;C:P is lower,and the availability of phosphorus in summer pasture is higher;the average ratio of N:P in summer pasture is higher.Compared with the national average of soil stoichiometric ratios,it was found that soil organic carbon in summer pastures and winter pastures decomposed well,producing sufficient nitrogen,and the availability of soil phosphorus was high,and the soil stoichiometric ratio was mainly affected by nitrogen.and the impact on summer pastures was higher than that on winter pastures.（6）The fluctuation range of the correlation between soil physicochemical factors and SOC,STN and STP contents in different slopes of pastures in summer is 0.5-0.86,0.53-0.89,0.51-0.89,and the fluctuations of soil physicochemical factors and SOC,STN and STP contents in different slopes of pastures in winter The range is 0.49-0.88,0.61-0.86,0.52-0.88,among which,soil temperature（ST）,soil water content（θ）,soil conductivity（EC）and other nutrient elements have a high positive correlation with them,respectively,Soil bulk density（ρ）and soil p H showed a negative correlation of more than medium degree,and there was a high correlation degree of more than 0.77between SOC,STN and STP.The correlations between ST,θ,EC and SOC,STN,and STP contents on the northern slopes of summer pastures and winter pastures were higher than those on the southern slopes.Compared with the southern slope,the content has a higher negative correlation.From the perspective of a single soil physicochemical factor,the correlation between ST,θ,EC and SOC,STN,and STP content in each slope aspect is that the winter pasture is greater than the summer pasture,and the relationship betweenρand SOC is higher.The correlation is that summer pastures are greater than winter pastures.This study clarified the differential changes and distribution characteristics of soil carbon,nitrogen and phosphorus content and vegetation communities on the slope gradient in Gannan seasonal pastures,which provided a certain reference for the grazing management of Maqu pastures in the future,and also contributed to the prevention and maintenance of grassland degradation and maintenance.A healthy and balanced alpine meadow ecosystem is of great significance.