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

豆科植物的根瘤有胞内细菌，可以将氮气固定成一种植物可以利用的氮。氢气是氮反应的副产物，占流向酶的能量的33%。豆科根瘤产生大量氢气，并将其释放到土壤中。例如，仅在加拿大的苜蓿作物中，我们估计每年可能有多达240亿升的氢气释放到加拿大的农业土壤中。这种氢气生产可以使用整个植物光合作用衍生能量净增益的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细菌的选择没有减少所有豆科植物的能量损失。豆类是与其他作物（特别是谷类作物）轮作的理想作物，可显著提高后续作物的生长和产量。在非豆科作物的生长增长中，只有约25%可归因于氮营养的改善。其余75%的影响无法解释。我们提出根瘤释放的氢刺激和支持某些土壤氧化氢细菌的生长。这些细菌反过来促进植物生长。本研究的目的是：1)利用T-RFLP分析这些土壤群落的细菌群落结构变化，并根据T-RFLP结果通过筛选PCR文库对“不可培养”的结核/ h2增强菌群进行鉴定；2)从氢处理土壤和HUP根瘤根际培养氧化氢细菌；3)在可控的温室条件下对这些微生物（以及先前分离的微生物）进行检测，以获得大量促进生长的特性；最后4)用有希望的菌株接种谷类作物种子，并在田间条件下检测有益效果。我的长期研究目标是了解植物根系与土壤微生物的关系，特别是对非豆科作物植物的促进作用，为农业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.