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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. [ABSTRACT FROM AUTHOR]

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The policy‐driven "Grain for Green Programme" (GGP) has resulted in large‐scale land conversion from agricultural land to natural land in the karst area. One research surrounding the GGP is focused on evaluating its ecological implications for total mercury (THg) enrichment in Yinjiang County, Guizhou Province, Southwest China. Results show that 1) THg content in agricultural land (201.85 ± 57.23 µg kg−1) is lower compared to the forest (1048.62 ± 306.19 µg kg−1) and shrub (2582.60 ± 614.76 µg kg−1). 2) The THg content shows a good correlation with Fe (agricultural land: R = 0.75, p < 0.01; shrub: R = 0.88, p < 0.01), pH (shrub: R = 0.87, p < 0.01), and sand proportion (forest: R = −0.65, p < 0.01), rather than soil organic carbon (SOC). In the shrub, the increased pH and iron (Fe) content correspond to THg content between 1804 and 3743 µg kg−1; below the depth of 80 cm of the forest soil, the increased sand proportion correlates to THg content between 1223 and 748 µg kg−1. 3) The risk index of the THg exceeds 320 in the soil and imposes a very high ecological risk to this area. [ABSTRACT FROM AUTHOR]