Study On Spatial Distribution Pattern Of Soil Carbon-Nitrogen-Phosphorus In Alpine Grassland On Qinghai-Tibet Plateau

In order to clarify the spatial distribution pattern of soil carbon-nitrogen-phosphorus in alpine grasslands on the Qinghai-Tibet Plateau,this study took the vegetation and soil of alpine meadows and alpine grasslands in the alpine grassland ecosystem of the Qinghai-Tibet Plateau as the research object.and indoor measurement,2420,2400,2200,1800 soil samples were collected and measured at depths of 0-10,10-20,20-30,and 30-50 cm,respectively.Soil organic carbon,total nitrogen,total phosphorus,available nitrogen,Available phosphorus as research indicators,with biological factors,climate factors,geographical factors,soil properties as influencing factors,to explore the spatial distribution of soil carbon-nitrogen-phosphorus and its dominant environmental factors.The content of soil carbon-nitrogen-phosphorus in the alpine grassland ecosystem on the Qinghai-Tibet Plateau and its response mechanism to environmental factors were preliminarily explored,which provided an important theoretical basis for the study of the carbon-nitrogen-phosphorus cycle between soils in the alpine grassland ecosystem on the Qinghai-Tibet Plateau.Through the data analysis of the large-scale field survey and the second national soil survey from 2014 to 2016,the changes of soil carbon-nitrogen-phosphorus pools in the alpine grasslands of the Qinghai-Tibet Plateau were estimated,and the changes of soil carbon-nitrogen-phosphorus under the conditions of global climate change were discussed.It provides basic data for predicting the source-sink effect of the Qinghai-Tibet Plateau in the future and realizing the carbon-nitrogen-phosphorus sustainability of the ecosystem.The main research conclusions are as follows:（1）The spatial heterogeneity of soil carbon-nitrogen-phosphorus distribution on the Qinghai-Tibet Plateau showed an increasing trend from northwest to southeast.（2）The average soil organic carbon content of 0-10,10-20,20-30,and 30-50cm alpine meadows was 63.04±3.97,40.19±2.82,35.77±5.47,31.63±7.71 mg/g;alpine grassland soils The average value of organic carbon content in each layer was12.94±1.41,11.79±1.1,8.67±0.94,6.68±0.71 mg/g.The organic carbon content of each layer of soil in the alpine meadow was significantly higher than that in the alpine steppe.In the vertical direction,the soil organic carbon content of different vegetation types showed a downward trend,and the phenomenon of surface aggregation generally existed.Surface soil organic carbon（0-20 cm）in alpine meadow was mainly affected by soil properties and biological factors.Soil pH and above-ground biomass were the dominant factors driving the change of soil organic carbon.The 20-50cm soil organic carbon was mainly affected by climatic factors and biological factors.Annual precipitation and above-ground biomass were the dominant factors driving the change of soil organic carbon.Alpine steppe soil is mainly affected by biological factors and climatic factors.Above-ground biomass and precipitation are the dominant factors driving soil organic carbon changes.（3）The average value of soil total nitrogen content in alpine meadow is4.66±0.33,3.06±0.19,2.51±0.29,1.86±0.28 mg/g;the average value of soil total nitrogen content in alpine steppe is 1.28±0.15,1.24±0.15,0.94±0.12,0.87±0.11mg/g.The total nitrogen（0-20 cm）of the topsoil in the alpine meadow was mainly affected by soil properties and biological factors.Soil bulk density and above-ground biomass were the dominant factors driving the change of soil total nitrogen.The 20-50cm soil total nitrogen was mainly affected by climatic factors and biological factors,and precipitation was the dominant factor driving the change of soil total nitrogen.The surface soil total nitrogen（0-20 cm）of the alpine steppe is mainly affected by geographical and climatic factors.Longitude,annual mean temperature and annual precipitation are the dominant factors driving the change of soil total nitrogen.The total nitrogen in the 20-50 cm soil was mainly affected by soil properties and biological factors.Soil pH and above-ground biomass were the dominant factors driving the change of the 20-50 cm soil total nitrogen.（4）The average value of total phosphorus content in alpine meadow soil in each layer is 0.79±0.03,0.73±0.03,0.67±0.03,0.59±0.03 mg/g;the average value of total phosphorus content in alpine grassland soil in each layer is 0.5±0.03,0.49±0.03,0.47±0.03,0.51±0.04 mg/g.In the vertical direction,there was no significant change in soil total phosphorus among different vegetation types.Topsoil total phosphorus（0-30 cm）in alpine meadow was mainly affected by soil properties and geographical factors.Soil pH,soil bulk density and longitude were the dominant factors driving changes in soil total phosphorus.Soil total phosphorus（0-30 cm）in the alpine steppe was mainly affected by biological factors and geographical factors.Above-ground biomass and longitude of above-ground species diversity were the dominant factors driving changes in soil total phosphorus.The total phosphorus in 30～50 cm soil was mainly affected by geographical factors.（5）The ammonium nitrogen content of the alpine meadow soil was 24.34±1.33,16.7±0.89,13.44±0.79,12.24±0.79 mg/kg in each layer,and the distribution of the alpine grassland soil ammonium nitrogen content was 14.07±0.96,12.06±0.83,11.71±0.9,13.31±1.31 mg/kg;the nitrate nitrogen content of alpine meadow in each layer was 16.32±2.71,8.59±0.9,7.28±0.72,5.42±0.61 mg/kg,and the nitrate nitrogen content of alpine grassland The content in each layer was 11.81±3.29,6.77±1.16,5.00±0.67,4.11±0.47 mg/kg.The vertical influencing factors of ammonium nitrogen in alpine meadows changed from soil properties and geographical factors to climatic factors,and the dominant driving factors changed from soil pH and longitude to annual precipitation.The vertical influence factors of ammonium nitrogen in the alpine steppe changed from soil properties and biological factors to climatic factors,and the dominant driving factors were driven by soil pH and longitude changed to annual average temperature.（6）The content of available phosphorus in the soil of the alpine meadow was2.39±0.24,1.18±0.13,0.76±0.16,0.74±0.25 mg/kg in each layer,and the content of available phosphorus in the soil of the alpine grassland was 0.61±0.07,0.43±0.06,0.39±0.04,0.37±0.11 mg/kg.Soil available phosphorus in alpine meadow was mainly affected by above-ground biomass;soil available phosphorus in alpine grassland was mainly affected by soil properties.（7）The organic carbon density of the 0-20 cm soil in the alpine grassland ecosystem of the Qinghai-Tibet Plateau was 4.29 kg/m²,and the storage was 5.88 Pg.The density and storage of soil organic carbon in the alpine meadow were 5.58kg/m²and 5.88 Pg(1 Pg=10¹⁵g),which were significantly higher than those in the alpine steppe,which were 2.99 kg/m²and 2.18 Pg.The results show that alpine grasslands have acted as carbon sinks in the past three decades.（8）The nitrogen density of the 0-20 cm soil in the alpine grassland of the Qinghai-Tibet Plateau is 0.36 kg/m²,and the reserve is 0.49 Pg.The soil total nitrogen density and storage in the alpine meadow were 0.44 kg/m²and 0.29 Pg,respectively,which were significantly higher than those in the alpine steppe,which were 0.27 kg/m²and 0.2 Pg.Over the past three decades,soil nitrogen pools in alpine grasslands have shown an increase.（9）The 0-20 cm soil phosphorus density in the alpine grassland of the Qinghai-Tibet Plateau is 0.1 kg/m²,and the reserve is 0.14 Pg.The soil total phosphorus density and storage in the alpine meadow were 0.09 kg/m²and 0.06Pg,respectively,which were lower than 0.11 kg/m²and 0.08 Pg in the alpine grassland.Over the past three decades,soil phosphorus pools in alpine grasslands have decreased.