Nutrient dynamics (N, P, S) through soil microbial biomass in root-zone

微生物量(生物量)作为氮、磷、硫等矿质养分的源和汇，对土壤肥力起着非常重要的作用(S)。在生物质周转期间，植物可以利用生物质中所含的营养物质。关于根分泌物在生物量形成中的作用或生物量中所含的营养物质对植物营养的作用的研究很少。通过土壤培养试验和土壤-植物根系试验，研究了生物量对根源化合物的利用，估算了生物量形成的养分需要量(N、P、S)和植物对生物量中养分的利用，研究了生物量形成对土壤中磷迁移的影响。植物体内约0.5%的~(14)C-光合作用产物被掺入生物量。这表明生物量利用根系释放的有机碳化合物作为碳源进行生物合成和能量供应(Supple.土壤姐妹和植物营养，46，32,20000)2.生物质中N、P和S的临界浓度(定义为达到生物质C最大合成的80%所需的浓度)分别为85、62和11mgg~(-1)生物量。氮素示踪结果表明，土壤含N量在20mgN kg~(-1)以上时，植物可利用生物量中的N。生物量P的周转时间是生物量C的两倍多，葡萄糖的周转时间约为37天，黑麦草(土壤生物)的周转时间约为42天。&Bioch.，32,845-852,2000，Biol.费蒂尔。土壤，32,310-317,2000，土壤生物学。用改良的多个隔室组成的根箱系统研究了土壤-植物根系中磷的分布。生物量的形成似乎促进了磷在土壤中的运移。

The microbial biomass (biomass) plays a very important role in soil fertility both as a source and sink for mineral nutrients, such as nitrogen (N), phosphorus (P) and sulfur (S). The nutrients held in the biomass may become available to plants during biomass turnover. There have been very few studies on the role of roots exudates in biomass formation or the role of nutrients held in the biomass for plant nutrition. Soil incubation experiments and soil-plant roots system experiments were conducted 1) to investigate the utilization of root-derived ^<14>C-labelled compound by biomass, 2) to estimate nutrient requirements (N, P, S) of biomass formation and the utilization of nutrients held in the biomass by plant-roots, and 3) to study the effects of biomass formation on the movement of P in soil.1. About 0.5% of ^<14>C-photosynthate in plants was incorporated into the biomass. This shows that ^<14>C-organic compound released by the roots is utilized by the biomass as C-substrate for biosynthesis and energy supply (Supple. of Soil Sce ＆ Plant Nutri., 46, 32,20000).2. The critical N, P and S concentration in biomass (defined as that required to achieve 80% of the maximum synthesis of biomass C) was estimated to be 85, 62 and 11mg g^<-1> biomass respectively. It was clarified by using ^<15>N tracer that N held in the biomass could be utilized by plants under the N concentration above 20mgN kg^<-1> soil. Turnover time of biomass P was more than twice as fast as that of biomass C and it was estimated to be about 37 days for glucose and 42 days for ryegrass (Soil Biol. ＆ Biochem., 32, 845-852, 2000, Biol. Fertil. Soils, 32, 310-317, 2000, Soil Biol. ＆ Biochem (in press))3. The distribution of P in soil-plant roots system was examined by the improved rhizobox system composed of several compartments. It seemed that the movement of P in soil was stimulated by the biomass formation.