Plant-soil feedback and species coexistence: interactions among soil pathogens, irradiance, and species life histories

长期以来，生态学家一直对这么多树种如何在给定的森林中共存感到困惑。该项目的主要目标是将两种看似不相关且相互竞争的机制联系起来，这两种机制已被提出用于树种共存。这是树木对光照的反应，以及对同一物种其他个体密度的增加或接近度的反应。树苗对土壤真菌的响应可能是树苗对光有效性和同一树种其他个体密度响应的关键。对于许多物种来说，在低光环境中，与其自身物种相关的土壤病原体对幼苗的死亡率可能会提高，而在被认为“不耐阴”的物种中，这种情况更为普遍。此外，这些生物植物-土壤反馈可能在加强物种对光反应差异方面发挥重要作用。该研究可能有助于更好地定义树荫耐受性和解释树种共存；这两个结果对于有效保护和管理温带森林都是至关重要的。例如，研究结果可能对森林恢复或木材工业产生影响，涉及需要特殊光照或再生困难的树种。此外，该项目将在植物和土壤微生物生态学方面对本科生进行教育、培训和指导，并为当地K-12教师和学生提供公共宣传。该项目的主要目标是研究生物植物-土壤反馈，这些反馈可以影响距离和密度依赖的幼苗在不同光照梯度和具有不同生活史特征的树种之间的生存和生长。研究人员将采用一种新的基于真菌排除罐的田间移植试验，研究树木幼苗对以下两种情况的响应机制：1)植物与土壤微生物群落之间的反馈作为光有效性的函数；2)幼苗对弱光的响应作为这些反馈的函数，这些反馈在幼苗的遮荫耐受性、当地成虫丰度以及与丛枝菌根真菌和外生菌根真菌的关联方面存在差异。因此，本研究将探讨植物-土壤反馈不仅通过负密度依赖过程促进物种共存的程度，而且还作为物种轻梯度分配的驱动因素。该项目还将调查哪些因素（例如，土壤病原体密度和组成，和/或幼苗性状）在弱光条件下造成疾病和植物-土壤反馈的更大负面影响。

Ecologists have long been puzzled about how so many tree species can coexist within a given forest. The main goal of the project is to link two seemingly unrelated and competing mechanisms that have been proposed for tree species coexistence. These are how tree species respond to light availability and to increasing density or proximity of other individuals of the same species. Tree seedling response to soil fungi may hold the key to tree seedling response to light availability and densities of other individuals of the same species. Seedling mortality to soil pathogens associated with their own species is likely enhanced in low light environments for many species, and much more prevalent in species considered 'shade intolerant'. In addition, these biotic plant-soil feedbacks may play a large role in heightening differences among species in their responses to light. This research may help to better define shade tolerance and explain tree species coexistence; both results are vital for effective conservation and management of temperate forests. For instance, results may have implications for forest restoration or the timber industry with regards to tree species with specific light requirements or regeneration difficulties. Additionally, this project will educate, train and mentor undergraduate students in plant and soil microbial ecology as well as provide public outreach to local K-12 teachers and students. The primary goal of the project is to investigate biotic plant-soil feedbacks that can affect distance- and density-dependent seedling survival and growth across light gradients and among tree species with varying life-history traits. The researchers will employ a novel field-based transplant experiment using fungal exclusion pots, which will investigate the mechanisms of tree seedling response to: 1) feedbacks between plants and the soil microbial community as a function of light availability, and 2) response to low light as a function of these feedbacks for eight temperate tree species that vary in seedling shade tolerance, local adult abundance and association with arbuscular and ectomycorrhizal fungi. Thus, this research will investigate the degree to which plant-soil feedbacks contribute to species coexistence through not only negative-density dependent processes, but also as a driver of species light gradient partitioning. The project will also investigate which factors (e.g., soil pathogen density and composition, and/or seedling traits) contribute to greater negative effects from disease and plant-soil feedback in low light.