Microbial transitions in soil ecosystems under land use and climate change

背景资料：土壤微生物组包括多种多样的微生物生命，在调节土壤地球化学循环和植物生长方面起着至关重要的作用。然而，我们对调节土壤微生物组动态和功能的因素及其抵抗和恢复扰动的能力的理解仍然很差，例如与集约土地利用和气候变化相关的扰动。除此之外，人们对土壤微生物组向替代状态过渡的脆弱性也知之甚少，这对土壤功能和植物生长具有潜在的有害影响。在包括人类肠道在内的其他生态系统中，对扰动的反应是突然过渡到替代状态，这已被广泛记录;但在土壤微生物群落中缺乏对过渡到替代稳定状态以及触发它们的因素的研究。鉴于土壤微生物群落日益受到与土地使用和气候变化有关的多种同时发生的扰动的挑战，以及新出现的证据表明：（a）严重干旱等离散扰动可引发突然转变为其他微生物状态，对土壤功能产生影响，这是一个重要的知识空白;和（B）土地利用历史可以改变土壤微生物群落对干旱的反应，更容易在以前集约农业下的土壤中过渡到替代状态。该奖学金将解决这些知识差距，并提供对反复干旱引发土壤微生物组分类和功能状态转变的能力的综合理解，以及这些转变的阈值如何通过土地利用历史进行修改。该奖学金将专注于干旱，因为干旱的风险是全球普遍存在的，预计在世界大部分地区，干旱频率和强度增加，并在草原土壤上，鉴于我们过去的BBSRC资助的工作表明，他们的微生物群落对土地利用变化高度敏感。目的：该研究旨在了解是什么使土壤微生物组容易过渡到替代状态，并确定土壤功能和植物生长的后果。具体来说，学生将测试的假设：（a）反复干旱触发土壤微生物组的变化，土壤养分循环和植物性能的负面影响的替代状态;和（B）土壤微生物组形集约土地利用更容易过渡到替代状态比那些具有可持续管理的历史。通过测试这些假设，这项研究将不会促进对土壤微生物组易受替代分类和功能状态转变影响的因素的理解，但它也将告知这种脆弱性如何通过土地利用历史进行修改，这是可持续管理的关键。方法和方针：学生将使用一系列高度集成的受控环境和实地实验来测试这些假设，并将使用最先进的基因组和生物地球化学技术来询问土壤微生物组的分类和功能属性，并量化营养转移通过土壤系统响应扰动。具体而言，这将包括综合使用扩增子和宏基因组测序，结合干旱强度和频率的新实验操作，以测试微生物群落向替代状态过渡的脆弱性，并确定这些过渡的关键阈值，以及它们如何被土地利用历史所改变。实验将使用从良好的特性，长期的草地实验与治疗反映不同的土地利用历史，在过去的BBSRC资助的研究所使用的土壤。

Background: The soil microbiome, which encompasses a vast diversity of microbial life, plays a crucial role in regulating biogeochemical cycles and plant growth. Yet, our understanding of the factors that regulate the dynamics and functioning of the soil microbiome, and its capacity to resist and recover from perturbations, such as those associated with intensive land use and climate change, remains poor2. Added to this, remarkably little is also known about the vulnerability of the soil microbiome to transitions to alternative states, with potentially deleterious consequences for soil functioning and plant growth. Abrupt transitions to alternative states have been widely documented in other ecosystems in response to perturbations, including the human gut; but studies of transitions to alternative stable states, and the factors that trigger them, are lacking in soil microbial communities. This represents an important gap in knowledge given that soil microbial communities are increasingly challenged by multiple co-occurring perturbations associated with land use and climate change, and emerging evidence that: (a) discrete perturbations, such as severe drought, can trigger abrupt transitions to alternative microbial states with consequences for soil functioning; and (b) land use history can modify the response of soil microbial communities to drought, being more vulnerable to transitions to alternative states in soils previously under intensive agriculture. This studentship will tackle these gaps in knowledge and deliver an integrated understanding of the capacity of repeated drought to trigger transitions in the taxonomic and functional state of soil microbiomes and how thresholds for these transitions are modified by land use history. The studentship will focus on drought because the risk of drought is globally pervasive, with increases in drought frequency and intensity expected in most parts of the world, and on grassland soils, given our past BBSRC funded work showing that their microbial communities are highly sensitive to land use change4. Objectives: This studentship seeks to understand what makes soil microbiomes vulnerable to transitions to alternative states and determine consequences for soil functioning and plant growth. Specifically, the student will test the hypotheses that: (a) repeated drought triggers shifts in soil microbiomes to alternative states with negative consequences for soil nutrient cycling and plant performance; and (b) soil microbiomes shaped intensive land use are more vulnerable to transitions to alternative states than those with a history of sustainable management. By testing these hypotheses, this studentship will not advance understanding of the factors that make the soil microbiome vulnerable to transitions to alternative taxonomic and functional states, but also it will inform on how this vulnerability is modified by land use history, which is key to sustainable management. Methods and approach: The student will test these hypotheses using a series of highly integrated controlled-environment and field-based experiments and will use state-of-the-art genomic and biogeochemical technologies to interrogate taxonomic and functional attributes of the soil microbiome and quantify nutrient transfers through the soil system in response to perturbations. Specifically, this will include integrated use of amplicon and metagenomics sequencing, in combination with novel experimental manipulation of drought intensity and frequency, to test the vulnerability of microbial communities to transitions to alternative states and to identify critical thresholds for these transitions, and how they are modified by land use history. Experiments will be done using soils taken from well characterized, long-term grassland experiments with treatments reflecting different land use histories, as used in past BBSRC funded research.