Rotation benefit and population changes of soil hydrogen oxidizing bacteria in legume crop fields

豆类的根瘤具有胞内细菌，可以将氮气固定为植物可以利用的一种形式的氮气。氢气是氮气反应的副产品，约占流向该酶的能量的33%。豆科植物根瘤会产生大量的氢气，并将其释放到土壤中。例如，仅在加拿大的紫花苜蓿作物中，我们估计每年可能有多达24亿升氢气释放到加拿大农业土壤中。这种氢气生产可以使用整个工厂光合作用产生的能量净收益的6%。我们不明白为什么进化过程、农作物的植物育种或最佳固氮菌的选择不能减少所有豆类的能量损失。豆类是与其他作物(特别是谷类作物)轮作的理想作物，可显著提高后一种作物的生长和产量。只有大约25%的非豆科作物的生长增长可以归因于氮素营养的改善。其余75%的影响无法解释。我们提出，根瘤释放的氢能刺激和支持某些土壤氢氧化菌的生长。这些细菌反过来又促进了植物的生长。本研究的目的是：1)利用T-RFLP分析土壤细菌群落结构的变化，并根据T-RFLP分析结果，通过PCR文库筛选出不可培养的根瘤菌群；2)从氢气处理的土壤和HUP根瘤根际培养氢氧化菌；3)在温室条件下对这些微生物(以及以前分离的微生物)进行多种促生长特性的测定；最后，将优良的细菌菌株接种到粮食作物种子，并在大田条件下进行有益效果的测试。本研究的长期目标是了解植物根系与土壤微生物的关系，特别是那些促进非豆科作物生长的微生物，为农业生产提供实用的方案或接种剂。

Root nodules of legumes have intracellular bacteria that can fix nitrogen gas into a form of nitrogen that the plant can use. Hydrogen gas is a byproduct of the nitrogen reaction, claiming about 33% of the energy that flows to the enzyme. Legume nodules produce a large quantity of hydrogen gas, and release this into soils. For example, in Canadian alfalfa crop alone, we have estimated that there may be as much as 2.4 thousand million liters of hydrogen gas released to Canadian agricultural soils every year. This hydrogen gas production can use up to 6% of the net gain of photosynthetically derived energy of the entire plant. We do not understand why evolutionary processes, plant breeding of agricultural crops, or selection of optimal nitrogen fixing bacteria has not reduced this energy loss in all legumes. Legumes are ideal crops to use in rotation with other crops (especially cereal crops), resulting in a significant increase in the growth and yield of the subsequent crop. Only about 25% of the increase in the growth of the non-legume crop can be attributed to improved nitrogen nutrition. The remaining 75% of the effect have eluded explanation. We are proposing that the hydrogen released by nodules stimulates and support growth of certain soil hydrogen-oxidizing bacteria. These bacteria in return promote plant growth. The purposes of this study are to 1) analyze the soil bacterial community structure changes in these soil communities by T-RFLP, and characterize the "unculturable" nodule/H2-enhanced bacterial populations by screen PCR library according to the T-RFLP results; 2) culture hydrogen oxidizing bacteria from hydrogen-treated soil and the rhizosphere of HUP- nodules; 3) assay these microbes (and previously isolated microbes) for a multitude of growth-promoting traits under controlled greenhouse conditions, and finally 4) inoculate cereal crop seeds with promising bacterial strains, and assay for beneficial effects under field conditions. The long-term goal of my research is to understand the relationship between the plant roots and soil microorganisms, especially the ones promoting the non-legume crop plants, to provide the practical protocols or inoculants for agriculture.