Study On Ecological Stoichiometry Characteristics Of Soil Organic Carbon, Nitrogen And Phosphorus In Tianlaochi Catchment Of Qilian Mountains

Tianlaochi catchment is a typical district in the upper reaches of Heihe River.Its soil is chosen as a research object in four vegetation types.Statistical analyses are used to study the distribution of soil organic carbon,nitrogen and phosphorus,and its ecological stoichiometry in picea crassifolia,Sabina przewalskii,subalpine shrub and Steppe.Meanwhile,we investigate the relationships between soil physical properties and soil organic carbon,nitrogen and phosphorus,and between soil physical properties and its ecological stoichiometry characteristics.Our results provide evidences about the spatial features of soil nutrients and theoretical support for evaluating water conservative function.The main conclusions are as following:(1)The contents of carbon,nitrogen and phosphorus in four vegetation types increase with elevation.However,The contents of phosphorus decrease with elevation in subalpine meadows.No significant differences in C:N ratio are found among vegetation types,and C:P and N:P ratio increase with elevation.(2)The contents of carbon,nitrogen and phosphorus decrease with increased soil depth in four vegetation types,having obvious surface assembly.The nutrient contents of 0~20cm soil depth are almost a half of 0~50cm soil depth.There are no significant differences between C:N ratio and soil depth,while C:P and N:P ratio decrease with increased soil depth.(3)In four vegetation types,the average contents of carbon are as follows: picea crassifolia> Sabina przewalskii> subalpine shrub> Steppe;The average contents of nitrogen are as follows: picea crassifolia> subalpine shrub> Sabina przewalskii > Steppe;The average contents of phosphorus are as follows: subalpine shrub > Sabina przewalskii > picea crassifolia > Steppe.C:N,C:P and N:P ratio in different vegetation types are revealed: picea crassifolia> Sabina przewalskii> subalpine shrub> Steppe.No significant differences in C:N,C:P and N:P ratio between Sabina przewalskii and subalpine shrub are detected.(4)Except for evaluation,soil depth and vegetation types,soil physical properties are are correlated with soil carbon,nitrogen and phosphorus and its ecological stoichiometry characteristics.Soil physical properties indirectly influence its distribution by affecting soil water contents,vent ability,soil water and heat status.According to the correlation and principal component analysis,the variability in soil carbon,nitrogen and phosphorus are affected by plenty of factors.The influences of each factor are random,and we hardly find a dominant factor which can decide the spatial distribution of soil carbon,nitrogen and phosphorus.(5)We obtain three principal components through principal component analysis.That is soil water condition,soil texture and soil pH.These components can,respectively,account for 53.11%,26.27% and 8.62% of the variability in soil C,N,P contents.This result indicates that the altitudinal gradient of soil carbon,nitrogen and phosphorus is mostly affected by soil water content,followed by soil texture and soil pH.In addition,bulk density,porosity and other factors can also affect the accumulation of soil carbon,nitrogen and phosphorus.