Studies on Role of Soil Microorganisms in Organic Nitrogen Uptake by Plants

通过绿色温室试验，分析了土壤中C和N的动态，包括水稻对有机氮的吸收。在示踪土壤中碳和氮时，<13><15>采用了低分子量和高分子量的碳和氮标记材料，如<13>碳-葡萄糖、氯化铵<15>、<13>碳和氮<15>双标记稻草堆肥、细菌和真菌。试验1中，水稻从基施葡萄糖中吸收碳的回收率<13>为：根1.8%，叶和茎0.8%，穗0.9%，表明水稻通过根吸收了大量的碳。在氮素处理中，根、茎叶和穗的回收率分别为9.2%、16.2%和27.2%。生长<13>前期和中期的半衰期分别为16和210天。说明<13>葡萄糖中的^ C被土壤微生物迅速吸收和代谢，但次生代谢产物的周转率较低。试验2中，水稻根系、茎叶和穗部对稻草堆肥中碳的吸收回收率分别为2.23%、1.35%和1.16%。在试验3中，施用的<13>细菌（枯草芽孢杆菌）中的^ C在根中的分配为2.13%，在叶和茎中的分配为7.41%，在穗中的分配为4.94%。真菌<13>（Aspergillusnigar）的碳在根中的分布较高，为19.3%，在叶和茎中为2.61%，在穗中为24.0%。这些结果表明，水稻从土壤微生物中吸收碳的能力是葡萄糖和稻草堆肥的4-13倍。因此，土壤微生物不仅可能是水稻根系直接吸收的分解者，而且可能是水稻根系直接吸收的重要基质。

Green house experiments were conducted in order to analyze C and N dynamics in soil, including organic nitrogen uptake by rice plant. For tracing C and N in soil, ^<13>C and ^<15>N labeled materials with low or high molecular weight were used such as ^<13>C-glucose, ^<15>NH4CL and ^<13>C and ^<15>N dual-labeled rice straw compost, bacteria, and fungi In experiment 1, the recovery percentages of rice uptake of ^<13>C from glucose applied into the soil at the basal fertilization were 1.8 % in root, 0.8 % in leaf and stem, and 0.9% in ear, indicating paddy rice absorbed a significant amount of C by root. On the other hand in nitrogen, higher recovery was observed as following, root (9.2 %), leaf and stem (16.2 %), and ear (27.2 %). The half life period of ^<13>C at early and mid growth stage was 16 and 210 days, respectively. It indicated that the ^<13>C in glucose was quickly absorbed and metabolized by soil microbes but the secondary metabolic products had a lower turnover rates. In experiment 2, recovery rate of plant uptake of C from rice straw compost were 2.23 % in root, 1.35 % in leaf and stem, and 1.16 % in ear. In experiment 3, ^<13>C in bacteria (Bacillus subtilis) applied was distributed to 2.13 % in root, 7.41 % in leaf and stem, and 4.94 % in ear. Higher distribution was observed in ^<13>C in fungi (Aspergillus nigar) as 19.3 % in root, 2.61 % in leaf and stem, and 24.0 % in ear. These results indicate that rice plant took up C more favorably at 4-13 times from soil microbes than glucose or rice straw compost. Therefore, soil microorganisms possibly play not only a role of decomposer but also that of important substrates for direct absorption by rice root.