Spatial variation analysis of soil carbon, nitrogen and phosphorus eco-stoichiometric ratios in karst and non-karst areas of Guangnan county, Yunnan, China

The ratio of soil carbon, nitrogen and phosphorus is an important indicator of soil organic matter composition and quality. However, soil has a high degree of spatial heterogeneity. In karst areas, the composition of soil geochemical elements is special, the ecological environment is vulnerable, and the natural environment is vignificantly different from non-karst areas. Therefore, it is necessary to understand spatial and temporal distributions and the migration mechanism of essential elements, such as carbon, nitrogen and phosphorus, for vegetation growth in the soils of both karst areas and non-karst areas. The study area of current study is located in Guangnan county, Yunnan Province, where karst areas account for 197.52 km2 and non-karst areas for 205.39 km2. The soil composition data for 102 surface composite soil samples and 24 deep composite soil samples were obtained from the soil geochemical survey on the scale of 1∶250,000. In this paper, one-way ANOVA, multiple comparison analysis and geostatistical method were utilized to compare the characteristics of soil carbon, nitrogen and phosphorus eco-stoichiometry and spatial variability between karst areas and non-karst areas, so as to explore the possible factors leading to this spatial variability and provide a reliable basis for ecological environment management and soil remediation. The results showed that in general, the contents of soil organic carbon(SOC), total nitrogen(TN) and total phosphorus(TP) in the karst area were significantly higher than those in the non-karst area, while the carbon to nitrogen ratio(C∶N) , carbon to phosphorus ratio(C∶P) and nitrogen to phosphorus ratio(N∶P) were significantly lower than non-karst area. Whether in karst areas or in non-karst areas, the content of SOC, TN and the C∶N, C∶P, N∶P ratio in the surface soil (0-20 cm) were significantly higher than those in the deep soil (>100 cm). Kriging interpolation results indicated that the contents of SOC, TN, TP in the surface soil were characterized by low in west and high in east of the study area; while the C∶N, C∶P, N∶P had a spatial distribution pattern of low values concentrated in the east and high values scattered in the west. In addition, there were differences in nutrient contents among different soil types, with the highest content of SOC, TN and TP in yellow-purple-mud soil and the lowest content of them in acid yellow-red soil. Natural factors, such as pedogenic parent rocks and soil types, have seriously controlled spatial variation of the soil carbon, nitrogen and phosphorus. Meanwhile, anthropic factors, such as land use change, also play an important role, which can not be ignored.