Explaining Variation in Legume-Rhizobium Mutualism

在许多自然和农业生态系统中，从珊瑚礁到依赖细菌(根瘤菌)获取氮的大豆植物，物种之间的合作非常重要。考虑到合作的好处，为什么有时合作会崩溃，就像珊瑚驱逐共生藻类或根瘤菌时漂白的情况一样，根瘤菌要么寄生在植物宿主上，要么完全忽视它们？之前由美国国家科学基金会资助的研究表明，植物减少了对根瘤菌的资源供应，而根瘤菌提供给它们的氮素更少，那么为什么在一些土壤中，不那么有益的根瘤菌仍然很常见？也许它们通过隐藏在根瘤中更有益的根瘤来逃避宿主植物的制裁，或者它们可能以某种方式操纵宿主提供它们没有赢得的资源。这两个假说都将得到实验验证。其他实验将确定，记录在案的减少对效益较低的根瘤菌的氧气供应是植物减少这些根瘤菌繁殖和传播的主要方式，还是其他植物反应也很重要。这项工作最早的实际好处可能是农业，但了解物种之间的合作也与各种各样的生态问题有关，从珊瑚礁的衰落到入侵植物的传播。在共生中获得的理解适用于理解人类的社会制度。这些研究将为各级学生提供研究机会。

Cooperation between species is important in many natural and agricultural ecosystems, from coral reefs to soybean plants that depend on bacteria (rhizobia) for nitrogen. Given the benefits of cooperation, why does itsometimes break down, as in the case of bleaching when corals expel symbiotic algae, or rhizobia that either parasitize their plant hosts or ignore them altogether? Previous NSF-funded research showed that plantsreduce resource supply to rhizobia that provide them with less nitrogen, so why are less-beneficial rhizobia still common in some soils? Maybe they escape host plant sanctions by hiding inside root nodules with morebeneficial rhizobia, or maybe they somehow manipulate their hosts into providing resources they haven't earned. Both hypotheses will be tested experimentally. Additional experiments will determine whether a documented reduction in oxygen supply to less-beneficial rhizobia is the primary way that plants reduce the reproduction and spread of these rhizobia, or whether other plant responses are also important. The earliest practical benefits of this work are likely to be agricultural, but understanding cooperation between species is also relevant to a wide variety of ecological problems, from the decline of coral reefs to the spread of invasive plants. The gained understanding in symbiosis applies to understanding human social systems. The studies will provide research opportunities for students at all levels.