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

通过温室试验，分析了土壤中碳、氮的动态变化，包括水稻对有机氮的吸收。为了示踪土壤中的C和N，使用了低分子量和高分子量的标记材料，如葡萄糖、NH4CL和稻草堆肥、细菌和真菌。试验一，稻草堆肥、细菌和真菌对水稻吸收的回收率；基施时土壤中葡萄糖碳含量为根1.8%，叶和茎0.8%，穗0.9%，说明水稻根系吸收了大量的碳。氮素利用率较高的依次为根(9.2%)、叶和茎(16.2%)、穗(27.2%)。生长前期和中期的半衰期分别为16天和210天。结果表明，葡萄糖中的~(13)C能迅速被土壤微生物吸收代谢，但次生代谢产物的周转率较低。在试验2中，水稻秸秆堆肥对碳的吸收回收率为：根2.23%，叶和茎1.35%，穗1.16%。在试验3中，所用细菌(枯草芽孢杆菌)中的13&gt；C在根中的分配比例为2.13%，在叶和茎中的分配比例为7.41%，在穗中的分配比例为4.94%。~-lt；13&gt；C在真菌中的分布较高，根19.3%，叶和茎2.61%，穗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或稻草堆肥的4-13倍。因此，土壤微生物可能既是分解者，又是水稻根系直接吸收的重要底物。

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.