| In order to clarify the interaction mechanism among carbon,nitrogen and phosphorus and provide the theoretical basis data,it is of great importance to investigate the contents of carbon,nitrogen and phosphorus of vegetation and soil and its stoichiometric characteristics in the alpine ecosystems of the Qinghai-Tibet Plateau.We studied the plant and soil samples of different vegetation types in the middle and eastern Qinghai-Tibet Plateau.Based on field survey and laboratory experiment,the characteristics of C,N,P,C:N,C:P,N:P ratios and their influencing factors were discussed.This study indicated that the mechanism of plant and soil carbon,nitrogen and phosphorus and its stoichiometric characteristics as well as its response to environmental changes in the Qinghai-Tibet Plateau ecosystem.The correlations between plant and soil C,N,P and its stoichiometric characteristics were also concluded.Major results and conclusions are as follows:(1)In this study,the average organic carbon and total nitrogen content of plant samples were 368.23g·kg-1 and 12.66g·kg-1 respectively.The organic carbon and total nitrogen content of forest land were both the highest,while in the shrub grassland were both the lowest.In addition,the average OC content of forest land was higher than that of shrub grassland and wild grass ground significantly.The average TN content of forest land was higher than that of shrub grassland significantly.The average total phosphorus content of vegetation samples were 07g·kg-1.The total phosphorus content of wild grass ground was the highest,and significantly higher than that of shrub grassland and alpine steppe,but not significantly different from forest land,alpine meadow and grassland.(2)The average C:N ratio of vegetation in the study area was 31.23;C:P average value was 401.52 which was significantly higher than the global average of 232;N:P average value was 13.68 which was significantly lower than the global average of 13.8 and lower than the national average of 16.3.Specifically,the vegetation of shrub grassland and alpine steppe were mainly restricted by phosphorus,while vegetation of forest land,wild grass and alpine meadow were mainly affected by nitrogen and phosphorus or neither element was missing,the grass was mainly restricted by nitrogen.(3)In this study,the average value of soil organic carbon,total nitrogen and total phosphorus content were 22.01g·kg-1,1.61g·kg-1 and 0.53g·kg-1 respectively.The SOC,TN and TP content in the forest was the highest,while in the desert land was the lowest.(4)The C:N average of the surface soil was 15.24,which is higher than the C:N value of the surface soil in China(10?12).The average C:P of the soil in the study area was 40.1,which was lower than that of the surface soil C:P(135.88).The average N:P in the surface soil was 3.02,which was lower than the average of 9.3 in China.(5)The SOC TN and TP content in the soil profile decreased with soil depth deepening,and SOC,TN and TP content were mainly concentrated in the surface.The difference between C:N,C:P,N:P values and soil depth was closely related to the difference of soil TN and TP content.As an important physiological index,N:P value of the other vegetation types decreased with soil depth deepening hackly,except for the change of N:P value in alpine grassland and saline soil.(6)There was a significant positive correlation between vegetation total nitrogen and soil NO3--N through Pearson correlation analysis,while there was no significant correlation between plant carbon,phosphorus content with soil carbon,phosphorus content and their stoichiometry.In this study,the correlation between vegetation C,N,P as well as their stoichiometry and soil C:N,C:P,N:P in the soil was not obvious,and the vegetation carbon,nitrogen and phosphorus was not synchronized with the soil in the same period completely.(7)The Stepwise Regression Analysis showed that there was a negative correlation between plant OC and silt.TN was negatively correlated with clay,and TP was positively correlated with soil inorganic carbon.However,there was no significant correlation between vegetation C:N?C:P?N:P and each influential factors,because the variable does not enter the equation.(8)The results showed that the main factor affecting SOC was pH value.The environmental factors on TN ranked in order of importance were soil Alk,pH value and clay content.As for soil TP,the environmental factors ranked in order of importance were pH,altitude and Alk.The main factors affecting the C:N value were the annual mean temperature.For C:P and N:P,the main influential environmental factors were clay content in the Qinghai-Tibet Plateau. |
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