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

微生物生物量作为氮(N)、磷(P)和硫(S)等矿质养分的来源和汇，在土壤肥力中起着非常重要的作用。生物量中的营养物质在生物量周转过程中可以被植物利用。关于根系分泌物在生物量形成中的作用或生物量中所含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：1)生物量对根源性^<14> c标记化合物的利用；2)估算生物量形成对养分（N、P、S）的需求以及植物根系对生物量中所含养分的利用；3)研究生物量形成对土壤中磷运移的影响。植物中约0.5%的c -光合产物被纳入生物量。这表明根系释放的c -有机化合物被生物量用作c -底物进行生物合成和能量供应。土壤安全与植物营养， 46, 32,20000).2。生物量的临界N、P和S浓度（定义为达到最大生物量C的80%所需的浓度）估计分别为85、62和11mg g^<-1>生物量。用N <15>示踪剂澄清了在N浓度大于20mgN kg^< 1>土壤下，生物量中所含的N可以被植物利用。生物量P的周转时间是生物量C的两倍多，葡萄糖周转时间约为37 d，黑麦草周转时间约为42 d。学生物化学&。生物工程学报，32 (2):845-852,2000；Fertil。土壤，32(2),2000，土壤生态学报。生物化学（已出版）采用改良的多室根箱系统研究了磷在土壤-植物根系中的分布。土壤中磷的流动似乎受到生物量形成的刺激。

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.