Soil Carbon, Nitrogen and Phosphorus Fractions and Response to Microorganisms and Mineral Elements in Zanthoxylum planispinum ‘Dintanensis’ Plantations at Different Altitudes

Abstract

The Carbon (C), nitrogen (N) and phosphorus (P) fractions, mineral element concentrations, microbial density, and biomass in 0–10 and 10–20 cm soil fractions under Zanthoxylum planispinum ‘dintanensis’ plantations, were measured at altitudes of 531, 640, 780, 871, and 1097 m in the mountainous karst areas of Guizhou Province, Southwest China, and the correlations between altitude and the soil variables were analyzed. The results showed that: (1) with the increase in altitude, there was no significant linear change in C fractions, total N, effective N, microorganism density, or mineral element concentration in each soil layer; however, ammonium-N and nitrate-N concentrations gradually decreased, and the P fraction was higher at the highest altitude; (2) soil C, N, and P fractions, concentrations of microorganisms and mineral elements at the same altitude showed a surface aggregation effect; (3) principal component analysis identified the main indicators affecting C, N and P fractions as total calcium, effective calcium, effective iron, total zinc, and bacteria; (4) correlation analysis showed that both total N and C fractions were positively correlated with effective N and P fractions and that mineral element concentrations were more closely correlated with C, N, and (especially) P fractions than with microorganism abundance. Overall, the effect of altitude on C, N, and P fractions showed that the correlation with soluble organic carbon was stronger than particulate organic carbon and easily oxidized carbon, inorganic N was closer correlated than organic N, and organic P was closer correlated than inorganic P. In conclusion, it shows that research focusing on soil N conservation, nutrient stoichiometry balance, and application of mineral-rich element fertilizers is important for Zanthoxylum planispinum ‘dintanensis’ plantation maintenance.