Explaining Variation in Legume-Rhizobium Mutualism

物种之间的合作在许多自然和农业生态系统中都很重要，从珊瑚礁到依赖细菌（根瘤菌）获取氮的大豆植物。考虑到合作的好处，为什么它有时会破裂，就像珊瑚驱逐共生藻类或根瘤菌时发生的白化一样，这些细菌要么寄生在植物宿主身上，要么完全忽视它们？以前由美国国家科学基金会资助的研究表明，植物减少了根瘤菌的资源供应，从而减少了根瘤菌提供的氮，那么为什么不那么有益的根瘤菌在一些土壤中仍然很常见呢？也许它们通过隐藏在根瘤中与更有益的根瘤菌一起逃避宿主植物的制裁，或者它们以某种方式操纵宿主提供它们没有获得的资源。这两种假设都将通过实验进行验证。进一步的实验将确定是否记录的减少对不太有益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，或者其他植物反应是否也很重要。这项工作最早的实际效益可能是农业，但了解物种之间的合作也与各种各样的生态问题有关，从珊瑚礁的减少到入侵植物的传播。在共生关系中获得的理解适用于理解人类社会系统。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.