土壤微生物对硫素转化及有效性的控制作用

Roles of Microbial Biomass in Controlling the Transformations and Availability of Sulphur in soil

土壤微生物不仅是一个重要的S(硫)养分库,而且控制土壤S的转化及其作物有效性。在不同土壤,微生物生物量变化很大,从贫瘠耕地土壤(表层)的1t/hm 2(干物质)以下到肥沃草地土壤的10t/hm 2 以上。耕地表层土壤微生物生物S含量通常为4- 43kg/hm 2,一般相当或大于土壤有效S含量和植物S吸收量。土壤微生物生物S的全周转时间估计小于1 年。由于建立了新的土壤微生物生物S测定方法并结合同位素35S标记技术,S的微生物转化动力学研究取得了很多的进展。研究表明,外源有机物S在土壤中能迅速的转化为无机S和被微生物同化和转化,但对土壤有效S含量的影响却取决于它本身的C∶S比率。无机SO2-4 - S的转化是通过微生物的同化和有机转化进行的。元素S的氧化速度在不同土壤相差极大,其产生的SO2-4 - S有相当一部分(29% —57% )被微生物利用和转化为非提取态有机S。

Soil S deficiency rapidly spreads in the world and significantly affects the yields and quality of grain and animal production. As S is actively involved into complicate cycling in the atmosphericbiologicalsoil ecosystems, to improve understanding on the dynamics in the procceses of S cycling is the key toward an effective manipulation of S deficiency.Soil microbial biomass serves as an important reservoir of available S to plants and also is the needdle of S cycling in soils. In soils, the amount of the microbial biomass(dry matter) varys largely, from smaller than l t ha -1 in infertile arable soils to larger than 10 t ha -1 in rich grassland soils. Quantities of microbial biomass S in the surface layer(023 cm) of arable soils generally varies between 4 and 43 kg ha -1 , which in general is equivalent to or larger than those of soil available S and plant uptake S. It is estimated that the turnover time of the microbial biomass S is below l year.Reliable methods have been developed to measure the amount of microbial biomass S and to monitor the microbial transformations of S in soil. This leads breakthrough in understanding the dynamics (processes and rates ) in the transformations of S. Studies showed that S in organic materials incorporated into soils can rapidly be released to sulphateS, immobilized by the microbial biomass or transformed into soil organic fractions. However, effects of such incorporations on the amount of available S in soil are dependent on the C∶S ratio of the organic materials. The immobilization and subsequent organic incorporations of inorganicS(sulphate) are regulated by the microbial uptake and its turnover. The transformations of oxided elemental S show similar dynamic characters, as following oxidation, 29%57% of elemental S added to 3 Uk arable soils transformed into microbial biomass or nonextractable organic fractions.