利用15N2直接标记法研究水稻种植对稻田固氮量和固氮活性的影响

稻田固氮对土壤维持肥力有着重要的作用,但水稻种植与固氮菌及其活性之间的关系尚不清楚。本试验利用15N2直接标记法测定了下位砂姜土发育的简育水耕人为土在种水稻和不种水稻条件下的生物固氮量,及其在土壤不同层次(0~1、1~5、5~15 cm)和水稻中的分配,并通过实时荧光定量PCR技术测定了土壤中固氮菌nifH DNA及RNA基因数量。结果表明:种水稻处理显著提高了土壤各层固氮量,尤其提高了1~5 cm和5~15 cm土层土壤固氮量对总固氮量的贡献;种水稻处理的总固氮量是不种水稻处理的10.3倍;水稻植株中生物固定的氮占总固氮量的31.48%;在0~1 cm土层,种水稻处理显著提高了nifH RNA基因数量,而对nifH DNA基因数量的增加不显著。可见,水稻种植没有增加固氮菌的数量,稻田固氮量的增加是因为水稻种植极大地促进了固氮菌nifH基因的表达,提高了固氮菌的固氮活性。

Effects of Rice Planting on Nitrogen Fixation Amount and Activity in Paddy Field Using 15N2 Direct Labeling Method

Paddy N2 fixation plays an important role for soil fertility maintenance, however, the relationship between rice planting and activity of diazotrophs to fix N2 remains elusive. In this paper the amount of biological nitrogen fixation (BNF) and its distribution in different soil layers (0-1cm, 1-5cm, 5-15cm) and rice were measured by 15N2 direct labeling method. The abundances of bacteria, nitrogen fixing bacteria, active bacteria and active nitrogen fixing bacteria in soil were determined by real-time quantitative PCR(qPCR). The results showed that planting rice significantly increased the nitrogen fixation amount in each soil layer, and also increased the contribution of 1-5cm and 5-15cm layers to total nitrogen fixation. The total nitrogen fixation amount in rice planting treatment was 10.3 times higher than in the CK treatment. The fixed N2 allocated to rice plants accounted for 31.48% of the total nitrogen fixation. In the 0-1cm soil layer, rice planting significantly increased the total transcription number of nifH gene, but did not significantly increase the number of nitrogen fixing microorganisms. These results indicate that rice planting did not increase the number of nitrogen fixing bacteria. The increase of nitrogen fixation amount in rice field is because rice planting greatly promoted the expression of nifH gene of nitrogen fixing bacteria, thus improving the nitrogen fixation activity of nitrogen fixing bacteria.