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

豆科植物的根瘤有细胞内的细菌，可以将氮气固定成植物可以使用的氮的形式。氢气是氮反应的副产物，占流向酶的能量的33%。豆类根瘤产生大量的氢气，并将其释放到土壤中。例如，仅在加拿大苜蓿作物中，我们估计每年可能有多达240亿升的氢气释放到加拿大农业土壤中。这种氢气生产可以使用整个植物光合衍生能量净增益的高达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并没有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，可显著提高后茬作物的生长和产量。非豆科作物生长的增长中只有约25%可归因于氮素营养的改善。剩下的75%的影响无法解释。我们提出，结核释放的氢刺激和支持某些土壤氢氧化细菌的生长。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技术分析这些土壤群落中细菌群落结构的变化，并根据T-RFLP结果筛选PCR文库，对“不可培养”的根瘤/H_2增强细菌种群进行表征：2）从氢处理土壤和HUP-根瘤根际培养氢氧化细菌; 3）在受控的温室条件下测定这些微生物（和先前分离的微生物）的多种生长促进特性，最后4）用有希望的细菌菌株接种谷类作物种子，并在田间条件下测定有益效果。本研究的长期目标是了解植物根系与土壤微生物之间的关系，特别是促进非豆科作物生长的微生物，为农业提供实用的协议或接种剂。

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.