| Soil organic carbon,total nitrogen,and total phosphorus are important nutrients and eco-environmental factors,and their stoichiometric ratios are the main indicators reflecting the internal carbon,nitrogen,and phosphorus cycles in the soil.Accurately understanding the spatial-temporal characteristics of soil organic carbon,total nitrogen,total phosphorus,and their stoichiometric ratios,as well as influencing factors,is of great significance in responding to global warming and biogeochemical cycles.In order to reveal the response mechanism of soil organic carbon,total nitrogen,total phosphorus and stoichiometric ratio to climate change and human disturbance under different land use types,this study was based on 1617 soil surface samples from the second soil census in western Sichuan in 1980 s and1700 soil surface samples sampled in the field in 2010 s,according to geostatistics,used GS+and Arc GIS10.4 software to predict the spatial distribution of SOC,TN,TP and stoichiometric ratio in the study area during 1980 s and 2010 s.Finally,based on the data of temperature,precipitation,soil type,nitrogen and phosphorus fertilizer application in the past 30 years,using descriptive statistical analysis and analysis of variance to explore the spatial variability and influencing factors of soil carbon,nitrogen,phosphorus content and stoichiometric ratio.The result showed:(1)The average of SOC,TN,and TP in the surface soil of western Sichuan were 23.06,2.00,and 0.64 g/kg in the 1980 s,and were 21.15,1.95,and 0.97 g/kg in the 2010 s.During the past 30 years in study area,the average SOC in the study area showed a decreasing trend,TP showed an upward trend,and TN did not change significantly.The decrease in SOC and TN in forest and grassland soil was greater than that in cultivated land,and the increase in TP in forest and grassland soil was less than that in cultivated land.(2)The C/N,C/P,N/P ratios of the surface soils in western Sichuan were 11.79,48.56,and 4.20 in the 1980 s,and were 11.08,24.64,and 2.34 in the 2010 s.During the past 30 years in study area,the C/N,C/P,N/P ratios showed a downward trend.At the same time,the C/N,C/P ratios of cultivated soil and forest and grassland soils decreased similarly,and the N/P ratio of cultivated soils decreased more than forest and grassland soils.(3)SOC,TN,TP and C/N,C/P,N/P ratios in study area in the 1980 s and 2010 s were all affected by structural and random factors.At the same time,SOC,TN,TP content and C/N,C/P,N/P ratios in the two periods showed a decreasing spatial distribution trend from northwest to southeast.The high-value areas are mainly distributed in the northwestern plateau of Sichuan,and the low-value areas are mainly distributed in the mountainous areas of southwestern Sichuan and the basin-peripheral mountains.(4)The decline in SOC,TN and the increase in TP during the past 30 years are related to the increase of temperature,precipitation and increased application of nitrogen and phosphate fertilizers.Increased temperature and precipitation will aggravate the decline of SOC and TN in study area,and inhibit the accumulation of TP in the soil.At the same time,compared with forest and grassland soils,the increase of nitrogen and phosphorus fertilizer application in the soil has slowed down SOC and TN decrease,and promoted the accumulation of TP.(5)The decline of C/N,C/P,N/P ratios in study area during the past 30 years was related to the decrease of SOC,TN and increase of TP.And the decline of TN was significantly smaller than that of SOC,resulting in a downward trend in C/N.While the reason for the C/P and N/P decline is resulted from combine effects of TP accumulation and the reduction of SOC,TN.At the same time,because of the increase in the amount of nitrogen fertilizer applied to cultivated soil,this will supplement part of TN lost due to increased temperature and increased precipitation,caused the decline in the C/N ratio of cultivated soil less than forest grass. |
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