资源环境科技发展态势分析平台

Understanding how phosphorus (P) and nitrogen (N) fertilization influence the dynamics of other nutrients [particularly sulfur (S)] is essential for improving the integrated nutrient management of tropical plantations. This study investigated how adding P and N fertilizers would affect S dynamics in the soils of two tropical forest plantations. Specifically, we tested whether the addition of P and N alters the availability of exchangeable S and microbial biomass S (MBS) and, hence, arylsulfatase activity (AS) and ratios of AS to C- and/or N-acquiring enzyme activity in the 0-5 cm soil layer were measured. The sites contained both control plots (no fertilizer application) and plots with 6-year continuous fertilizer (P and N) application. Soil exchangeable S clearly decreased, while AS activity marginally increased in P-fertilized plots. The ratios of soil AS activity to C- and/or N-acquiring enzyme activity tended to increase, possibly because the requirements of microbes for S relative to C and N were elevated, with P fertilization exacerbating shortages in S. In comparison, N fertilization did not influence exchangeable S, soil pH, and MBS. This lack of response might be attributed to continuous deposition of high levels of background N at the study sites. Soil AS activity and the ratios of soil AS activity to C- and/or N-acquiring enzyme activity tended to be lowered by N fertilization; thus, AS activity might be more sensitive to N fertilization than to soil pH. In conclusion, P fertilization must be carefully managed in tropical forest plantations to minimize its negative impact on soil S availability.