陕北黄土区生物结皮条件下土壤养分的积累及流失风险

Soil nutrients accumulation and their loss risk under effects of biological soil crust in Loess Plateau of northern Shaanxi Province,China

分析了陕北黄土高原典型流域生物结皮的形成和发育对土壤养分的积累效应,同时对生物结皮条件下土壤养分的流失风险进行评价.结果表明:生物结皮生长发育后能够迅速增加结皮层及2cm土层的养分含量,但对深层土壤影响较小;退耕0～20年间结皮层的养分含量与退耕年限之间的关系可用指数函数(y=a[b-exp(-cx)])拟合,其中有机质、全氮和碱解氮在退耕20年间的增加速度变化不大,而全磷、速效磷和速效钾在退耕初期增加迅速,后期增加缓慢;自然发育生物结皮对土壤养分的年均净贡献量为:有机质50.15g.m-2、全氮1.95g.m-2、全磷0.44g.m-2、碱解氮164.33mg.m-2、速效磷9.64mg.m-2和速效钾126.21mg.m-2,人工培育条件下生物结皮发育更快,对养分尤其是速效养分的贡献速率更高;生物结皮条件下养分含量的提高增加了养分流失风险,尤其是养分随泥沙流失大幅度增加,生物结皮增加的养分中平均有39.06%随泥沙流失,仅有60.94%得以保留.总之,生物结皮可迅速、全面增加表层土壤养分,但同时会加大养分流失风险.尽管如此,土壤养分的净增加量仍相当可观,显示生物结皮具有较好的土壤养分积累效应.

The study on the soil nutrients accumulation and their loss risk under effects of biological soil crust （BSC） in a typical basin of Loess Plateau in northern Shaanxi Province showed that with the development of BSC, the nutrient contents in BSC and in 0-2 cm soil layer increased rapidly, but those in deeper layers had less change. Within the 20 years of rehabilitation, the relationship between the nutrient contents in BSC and the rehabilitation age could be described by the exponential equation （y = a[ b- exp（-cx） ] ）. The increasing rates of organic matter （OM）, total nitrogen （TN）, and available nitrogen （AN） in the 20 years changed less, but the contents of total phosphorus （ TP）, available phosphorus （ AP）, and available potassium （AK） increased very fast at first 5 years. The yearly average contribution of naturally developed BSC to soil nutrients was 50. 15 g · m^-2 of OM, 1.95 g · m^-2 of TN, 0.44 g· m^-2 of TP, 164. 33 mg· m^-2 of AN, 9.64 mg · m^-2 of AP, and 126. 21 mg · m^-2 of AK. Compared with naturally developed BSC, cultivated BSC had a faster growth rate, and its contribution to soil nutrients, especially to soil available nutrients, was greater. However, the increase of soil nutrients under effects of BSC could intensify the loss risk of soil nutrients with sediments. In this study, 39.06% of increased soil nutrients by BSC were lost with sediments, and 69. 04% of them were conserved. Therefore, even though the loss risk of soil nutrients was increased, their net accumulation was still significant, indicating that BSC had better effects on soil nutrients accumulation.