DISSERTATION RESEARCH: Mechanisms of microbe-mediated plant species coexistence across spatial and temporal scales

植物和它们看不见的微生物伙伴之间的相互作用在自然界中无处不在，但它们在推动植物多样性和共存中的作用尚未得到很好的理解。微生物促进植物共存的一种方式是通过植物-土壤的负反馈：植物经常在根部和土壤中积累特定物种的病原体。随着植物物种数量的增加，它们的病原体也在增加，这限制了它们的无限制生长，并可能成为一种允许多种植物物种共存的机制。这一机制已经在温室中进行了测试，但我们对其在自然界中的重要性知之甚少。本研究旨在研究植物-土壤反馈及其对植物物种之间竞争和共存的影响，首先在温室中进行测试，然后在田间试验中进行检验。新项目的重点是在田间和温室实验中培养和测序与植物相关的真菌，将回答以下问题：哪些微生物在植物-土壤反馈中最重要？它们对植物寄主有什么影响？这些影响是否取决于气候？这些调查结果将揭示两种基本干旱草地共存的驱动因素，并将与土地管理者分享，以改善管理。这项研究还将为本科生提供研究机会，并通过为学童提供夏令营经验和推广活动，增加公众对干旱土地生态系统的了解。大量的理论和机制模型预测植物-微生物的相互作用有助于物种共存，温室实验显示了微生物驱动的植物-土壤反馈（PSF）的大量证据。然而，对长期植被动态中PSF作用的实地试验对于确定PSF与其他共存机制（如在自然界中运行的空间非生物生态位变化）相比的相对重要性至关重要。论文工作通过将PSF的强度（在现场实验中测量）与共存稳定性的数十年变化联系起来，填补了这一空白。提出的改进将通过使用下一代测序方法和真菌培养物的定向温室接种来表征PSF的地下机制，从而解决论文工作中出现的问题。结果将通过增加从温室到田间的植物-微生物相互作用的规模能力来推进知识，解决真菌群落组成在空间和时间尺度上解释植被动态的程度，并确定一组知之甚少的真菌（暗隔内生菌）的生态作用，这有可能彻底改变目前关于植物如何应对非生物胁迫的范式。

Interactions between plants and their unseen microbial associates are ubiquitous in nature, yet their role in driving the diversity and coexistence of plants is not well understood. One way microbes could enhance plant coexistence is through negative plant-soil feedbacks: Plants often accumulate species-specific pathogens in their roots and soils. As a plant species increases in number, so do their pathogens, which limits unrestricted growth and can be a mechanism to allow coexistence of many plant species. This mechanism has been tested in the greenhouse, but we have little knowledge of its importance in nature. This research aims to investigate plant-soil feedbacks and its consequences for competition and coexistence between plant species by first testing it in the greenhouse, and then examining it in a field experiment. New projects that focus on culturing and sequencing the fungal associates of plants in the field and greenhouse experiments will answer questions such as: Which microbes are most important in plant-soil feedbacks? What are their effects on plant hosts? Are these effects dependent on climate? The results of these investigations will shed light on the drivers of coexistence in two foundational arid-land grasses, and will be shared with land managers to improve stewardship. This research will also provide research opportunities for undergraduate students, as well as increase public understanding of arid-land ecosystems via summer camp experiences for school children and outreach.Substantial theory and mechanistic models predict that plant-microbe interactions contribute to species coexistence, and greenhouse experiments show considerable evidence of microbe-driven plant-soil feedback (PSF). However, field tests of the role of PSF in long term vegetation dynamics are critical to determining the relative importance of PSF compared to other mechanisms of coexistence, such as spatial abiotic niche variation, operating in nature. Dissertation work fills that gap by linking the strengths of PSF (measured in field experiments) to decades-long variation in the stability of coexistence. Proposed improvements will resolve questions that have arisen from dissertation work by characterizing the belowground mechanisms of PSF using next-generation sequencing methods and targeted greenhouse inoculation of fungal cultures. Results will advance knowledge by increasing the ability to scale plant-microbe interactions from the greenhouse to the field, resolving the degree to which fungal community composition explains vegetation dynamics over spatial and temporal scales, and determining the ecological roles of a poorly understood group of fungi (dark septate endophytes), which has the potential to revolutionize current paradigms on how plants respond to abiotic stress.