EAGER: Collaborative research: Shifting control from negative plant-microbe feedback to nutrient limitation: predictions from dominant tree traits and ecosystem nutrient economies

森林生态系统因其生物多样性和对碳和养分循环的影响而具有全球重要性。在世界各地的森林中，真菌和树根形成了一种互利的关系，为真菌提供食物，以帮助树木获得土壤养分。这种关系日益被认为是预测森林长期动态的一个关键特征。根据真菌是生长在根细胞内（“丛枝菌根”）还是生长在根表面（“外生菌根”），树种可分为两类。本研究探讨了菌根树类型之间的生化差异是否对土壤微生物群落和植物群落的其他成员具有级联效应。具体来说，该项目将检验一个新的假设，即森林中优势树木形成的菌根类型决定了树木和其他植物是更有可能受到营养还是疾病（病原体）的限制。外生菌根树产生的叶和根组织比丛枝菌根树的组织更难分解，这降低了养分的有效性，但也降低了植物病原体持续存在的能力，因为许多病原体在活宿主之间的死亡植物组织上生长。因此，预计优势树种的菌根类型会创造一种土壤环境，要么降低养分有效性（在外生菌根树下），要么提高植物与病原体相互作用的速度和严重程度（在丛枝菌根树下）。该项目融合了关于植物种群和群落驱动因素的生态学理论，提供了一个强大的总体框架，可能会改变我们对树种组成变化如何影响未来生态系统动态的理解。项目成果还包括培训下一代科学家和一个公共森林恢复项目，该项目将建立不同菌根树类型的地块，吸引志愿者，帮助教育公众，并促进我们对森林恢复的理解。该研究将涉及实验操作和生物分析，以验证一个总体假设，即温带森林中营养限制和病原体介导的负反馈的相对重要性取决于优势树种的菌根共生类型，这是一套综合叶和根性状的指标。将研究三个具有先前表征的菌根梯度的地理区域。实验将包括控制养分和病原体丰度，以确定成树根系和树苗对不同土壤中假设的限制因素的反应。此外，微生物群落中的病原体将通过测序和分离来表征，流行的分离物将用于生物测定，以测试Koch的假设并确定它们影响植物群落组装的能力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Forest ecosystems are globally important due to their biological diversity and influence on carbon and nutrient cycles. In forests worldwide, fungi and tree roots form a mutually-beneficial relationship that provides food to fungi in return for helping trees gain access to soil nutrients. This relationship is increasingly recognized as a key trait for predicting long-term forest dynamics. Tree species can be divided into two categories based on whether the fungi grow inside the root cells ("arbuscular mycorrhiza") or on root surfaces ("ectomycorrhiza"). This research addresses whether biochemical differences between mycorrhizal tree types have cascading effects on the soil microbial community and other members of the plant community. Specifically, the project will test the novel hypothesis that the type of mycorrhizae formed by the dominant trees in a forest determines whether the trees and other plants are more likely to be limited by nutrients or by disease (pathogens). Ectomycorrhizal trees produce leaf and root tissue that is more difficult to decompose than the tissue from arbuscular mycorrhizal trees, reducing nutrient availability but also the ability of plant pathogens to persist since many pathogens grow on dead plant tissue when between live hosts. Thus, the mycorrhizal type of the dominant tree species is predicted to create a soil environment that either reduces nutrient availability (under ectomycorrhizal trees) or enhances the speed and severity of plant-pathogen interactions (under arbuscular mycorrhizal trees). This project merges ecological theories about drivers of plant populations and communities, providing a powerful general framework that may transform our understanding of how shifts in tree species composition affect future ecosystem dynamics. The project outcomes will also include training the next generation of scientists and a public forest restoration project that will establish plots of differing mycorrhizal tree types, engage volunteers, help educate the public, and contribute to our understanding of forest restoration.The research will involve experimental manipulations and bioassays to test the overarching hypothesis that the relative importance of nutrient limitation and pathogen-mediated negative feedbacks in temperate forests depends on the type of mycorrhizal symbiosis of dominant tree species, which is an indicator for an integrated set of leaf and root traits. Three geographic areas with previously characterized mycorrhizal gradients will be studied. Experiments will involve manipulating nutrient and pathogen abundance to determine the response of adult tree roots and establishing seedlings to the hypothesized limiting factors in different soils. In addition, pathogens in the microbial communities will be characterized through both sequencing and isolation, and prevalent isolates will be used in bioassays to test Koch's postulates and determine their ability to affect plant community assembly.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.