Collaborative research: Effects of herbivores and mycorrhizas on N-fixers across soil and climate gradients in the Serengeti

在自然和农业生态系统中，植物可利用形式的土壤氮和磷的短缺经常限制植物生产。土壤中的微生物可以帮助缓解这一限制，因为固氮细菌可以将大气中的氮气转化为植物可以利用的氮，而菌根真菌可以帮助植物获取磷。这些微生物被怀疑是生态系统生产力的重要调节者，但令人惊讶的是，人们对控制它们的丰度和活动的原因知之甚少。在东非塞伦盖蒂草原的研究提供了一个前所未有的机会，可以了解食草动物、它们所食用的植物和土壤微生物如何相互作用，从而产生一个非常稳定的生态系统。本研究将在两个新的操作实验和一个正在进行的长期放牧实验中应用尖端的分子方法，以评估食草动物和菌根真菌对土壤微生物丰度和固氮活性的刺激或限制程度，以及这些影响是否由降雨和土壤矿物质介导。如果固氮细菌和菌根真菌能得到更有效的管理，人类对化肥的依赖就能减少。这项工作将为制定管理战略提供科学基础，以最大限度地发挥这些土壤生物在半干旱草原、稀树草原和其他热带生态系统中可持续生产粮食和纤维的好处。这些结果还将使人们有可能更密切地估计自然氮输入的贡献，相对于全球范围内人为引起的氮沉积的增加。这项研究将在坦桑尼亚建立科学能力，因此这个奖项是由NSF的国际科学与工程办公室共同资助的。

Shortages of plant-available forms of soil nitrogen and phosphorus frequently limit plant production in natural and agricultural ecosystems. Microorganisms in the soil can help relieve this limitation, as nitrogen-fixing bacteria convert atmospheric nitrogen-gas into forms of nitrogen that plants can use, and mycorrhizal fungi help plants acquire phosphorus. These microorganisms are suspected to be important regulators of ecosystem productivity, but surprisingly little is known about what controls their abundance and activities. Research in the Serengeti grassland in East Africa provides an unprecedented opportunity to learn how herbivorous animals, the plants they consume, and soil microorganisms all interact together to generate a remarkably stable ecosystem. This research will apply cutting-edge molecular methods in two new manipulative experiments plus an ongoing long-term grazer exclosure experiment to assess how strongly herbivores and mycorrhizal fungi stimulate or limit the abundance and N-fixing activity of soil microbes, and whether these effects are mediated by rainfall and soil minerals. Human reliance on chemical fertilizers could be reduced if nitrogen-fixing bacteria and mycorrhizal fungi could be more effectively managed. This work will provide the scientific basis for developing management strategies to maximize the benefits of these soil organisms for sustainable production of food and fiber in semi-arid grasslands, savannas and other tropical ecosystems. The results will also make it possible to estimate more closely the contribution of natural nitrogen inputs, relative to elevated human-induced nitrogen deposition across the globe. The research will build scientific capacity in Tanzania, and hence this award is co-funded by NSF's Office of International Science and Engineering.