模拟氮沉降对华西雨屏区苦竹林土壤有机碳和养分的影响

从2007年11月至2009年10月, 对华西雨屏区苦竹(Pleioblastus amarus)人工林进行了模拟氮(N)沉降试验, N沉降水平分别为对照(CK, 0 g N·m^-2·a^-1)、低N (5 g N·m^-2·a^-1)、中N (15 g N·m^-2·a^-1)和高N (30 g N·m^-2·a^-1)。在N沉降进行1年后, 每月采集各样方0-20 cm的土壤样品, 连续采集12个月, 测定其土壤总有机C、微生物生物量C、浸提性溶解有机C、活性C、全N、微生物生物量N、NH₄⁺-N、NO₃^--N、有效P和速效K。结果表明: N沉降显著增加了土壤总有机C、微生物生物量C、全N、微生物生物量N、NH₄⁺-N和有效P含量, 对其余几个指标无显著影响。土壤微生物生物量C和微生物生物量N的季节变化明显, 并与气温极显著正相关。土壤有效P、速效K与微生物生物量C、微生物生物量N呈极显著负相关关系。N沉降提高了土壤中C、N、P元素的活性, 并通过微生物的转化固定作用使得C、N、P元素在土壤中的含量增加。苦竹林生态系统处于N限制状态, 土壤有机C和养分对N沉降呈正响应, N沉降的增加可能会提高土壤肥力并促进植被的生长, 进而促进生态系统对C的固定。

Response of soil organic carbon and nutrients to simulated nitrogen deposition in Pleioblastus amarus plantation, Rainy Area of West China

Aims Our objectives were to determine the effect of increased nitrogen deposition on soil organic carbon and nutrients of Pleioblastus amarus plantations. Methods Beginning in November 2007, we conducted a two-year field experiment of simulated nitrogen deposition in a P. amarus plantation, Rainy Area of West China. The levels of nitrogen deposition were 0, 5, 15 and 30 g N·m^–2·a^–1 for control (CK), low, medium and high nitrogen, respectively. For one year beginning in November 2008, we monthly collected 0–20 cm horizon soil samples and measured soil total organic carbon (TOC), microbial biomass carbon (MBC), extractable dissolved organic carbon (EDOC), liable carbon (LC), total nitrogen (TN), microbial biomass nitrogen (MBN), NH₄⁺-N, NO₃^–-N, available phosphorus (AP) and available potassium (AK). Important findings Nitrogen deposition increased concentrations of TOC, MBC, TN, MBN, NH₄⁺-N and AP in soil and had no effect on the other indicators. MBC and MBN exhibited significant seasonal patterns that were positively related to temperature. AP and AK were significant negatively correlated with MBC and MBN. Nitrogen deposition stimulated availabilities of C, N and P and increased the accumulation of these elements in the soil. Results suggested the P. amarus plantation ecosystem is N-limited and soil organic carbon and nutrients respond positively to nitrogen deposition. Increasing nitrogen deposition may enhance fertility of the soil, stimulate growth of plants and increase future carbon fixation.