Distribution characteristics and impact factors of soil microbial biomass car-bon, nitrogen and phosphorus in western Sichuan plain

The characteristics of soil microbial biomass carbon (MBC), soil microbial biomass nitrogen (MBN), and soil microbial biomass phosphorus (MBP) contents, and their responses to climate, altitude, parent material and land use in the western Sichuan plain were investigated by regional survey and statistical analysis. The key influencing factors were subsequently revealed, which provided theoretical guidance for soil quality management in western Sichuan plain. Results showed that MBC, MBN and MBP were significantly higher in alluvial soil than in paddy soil, fluvo-aquic soil, and yellow earth (P < 0.05); moreover, MBC/MBN of fluvo-aquic soil was significantly higher than that of paddy soil. With respect to the influence of climate and elevation, MBC, MBN, and MBP exponentially declined with increasing accumulated temperature above 0℃, accumulated temperature above 10℃, mean annual temperature (MAT) and mean annual precipitation (MAP). However, they were augmented with increasing aridity and altitude. For different parent soil materials, the soil that developed from gray alluvial soil had higher MBC, MBN and MBP contents than those developed from glacial till. Meanwhile, they were significantly higher in the grassland than in paddy field and dry land. However, there were no significant differences between paddy field, dry land, and forest land. Pearson correlation and redundancy analyses revealed that the MBC and MBN had highly significant negative relationships with accumulated temperature above 0℃ and MAT, while, they had highly significant positive relationships with altitude (P < 0.01). In addition, MBP had a highly significant negative relationship with parent material. Furthermore, stepwise regression analysis showed that the main impact factors for MBC were MAT, MAP, and parent material, and aridity; MBN was affected by altitude, aridity, and MAP; MBP was primarily controlled by parent material, accumulated temperature above 10℃, and MAP. Therefore, soil MBC, MBN and MBP can sensitively reflect the climate change in different sampling points in western Sichuan plain, providing an essential basis for predicting the response of soil carbon, nitrogen, and phosphorus to climatic changes.