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，植物可利用的土壤氮和磷的缺乏常常限制植物的生产。土壤中的微生物可以帮助缓解这种限制，因为固氮细菌将大气中的氮气转化为植物可以使用的氮的形式，而菌根真菌帮助植物获得磷。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因素知之甚少。在东非塞伦盖蒂草原的研究提供了一个前所未有的机会，了解草食动物，他们消费的植物和土壤微生物如何相互作用，共同产生一个非常稳定的生态系统。这项研究将在两个新的操纵实验中应用尖端的分子方法，再加上一个正在进行的长期食草动物封闭实验，以评估食草动物和菌根真菌如何强烈地刺激或限制土壤微生物的丰度和固氮活性，以及这些影响是否由降雨和土壤矿物质介导。如果能够更有效地管理固氮细菌和菌根真菌，就可以减少人类对化肥的依赖。这项工作将为制定管理战略提供科学依据，以便最大限度地利用这些土壤生物体，在半干旱草原、稀树草原和其他热带生态系统中可持续地生产粮食和纤维。研究结果还将使人们能够更准确地估计自然氮输入相对于地球仪上人为氮沉降增加的贡献。这项研究将建设坦桑尼亚的科学能力。

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.