SG: Quantifying the contribution of plant-soil feedbacks to coexistence in a sagebrush steppe

在许多自然生态系统中，可以发现几十种植物在非常小的区域内生长在一起。然而，100多年来，研究人员一直在努力解释为什么没有一个单一的物种可以排除所有其他物种。人们认为，只有当每个物种的竞争能力受到不同因素的限制时，它们才能共存。例如，它们可能需要不同的资源来生长，可能被不同的东西感染或吃掉，或者需要不同的环境条件。然而，事实证明，要证明这一观点在自然界中成立是困难的。该项目将建立在现有的关于鼠尾草草原植物共存的研究基础上。这项研究表明，最常见的植物物种是共存的，因为限制幼苗成功建立的因素不同。这些建立上的差异被怀疑是由于生活在土壤中并感染不同物种的根的真菌病原体的差异造成的。在这项研究中，研究人员将使用田间实验、温室实验和基于历史和实验数据的计算机模型来了解真菌病原体在维持植物物种共存方面的作用有多大。这项工作将研究的鼠尾草草原是一个具有经济和保护重要性的濒危生态系统。这项研究将对在这些系统中工作的土地管理者有用，因为它将增加对重要的本土植物物种在其更新中的帮助的理解。因此，这将导致改善管理和恢复这一生态系统的方式。研究结果将被用于编制供土地管理者使用的情况说明书，并将通过州、联邦、大学和非政府组织现有的对鼠尾草草原保护感兴趣的人员网络提供给他们和其他人。经验共存研究的进展需要将现代的、定量的方法，如人口模型，与经典的机械论方法，如针对特定共存机制的实验相结合。该提案将这些方法结合在一起，侧重于一种潜在的机制，该机制最近引起了人们的极大兴趣，可能对多年生植被很重要：植物-土壤反馈(PSF)。首先，田间试验将量化真菌PSFs在种内和种间对萌发、出苗和建立的影响。一个配套的温室实验将解决关于现场和基于实验室的PSF研究之间的差异的问题，并将此案例研究置于当前文献的背景下。其次，实地试验的结果将被纳入现有的现象学多物种种群模型，从而能够比较在只有PSF驱动招募阶段互动的情况下共存的总体稳定性，以及包括对招募的种内和种间影响的所有可能来源的情况下共存的总体稳定性。通过结合野外实验、温室研究、长期人口统计数据和模型，这项工作将量化PSFs对山艾树草原群落共存的总体稳定性的贡献。这种新颖的实验和建模框架可以在未来扩展到其他社区和共存机制。

In many natural ecosystems, dozens of plant species can be found growing together in very small areas. However for over 100 years researchers have struggled to explain why no single species can exclude all the others. It is thought that species can coexist only when the ability of each to outcompete the others is limited by something different. For example, they may each need different resources for growth, be infected by or eaten by different things, or need different environmental conditions. However, showing that this idea holds in nature has proven difficult. This project will build on existing research on plant coexistence in sagebrush steppes. This research shows that the plant species that are most common coexist because of differences in what limits how successful seedlings are at getting established. These differences in establishment are suspected to be caused by differences in the fungal pathogens living in the soil and infecting roots of the different species. In this study, the researchers will use a field experiment, greenhouse experiment, and computer models based on historical and experimental data to find out how big the role of fungal pathogens is in maintaining the coexistence of plant species. The sagebrush steppe that this work will study is an at-risk ecosystem that has economic and conservation importance. This research will be useful to land managers working in these systems, because it will increase understanding of how important native plant species can be helped in their regeneration. Therefore it will lead to improved ways to manage and restore this ecosystem. The results will be used to create fact sheets for use by land managers, and will be made available to them and to others through existing networks of state, federal, university and NGO personnel interested in sagebrush steppe conservation.Progress in empirical coexistence research requires integration of modern, quantitative approaches such as population modeling, with classical mechanistic approaches such as experiments targeting specific coexistence mechanisms. This proposal combines these approaches by focusing on one potential mechanism that has recently generated tremendous interest and is likely important in perennial vegetation: plant-soil feedbacks (PSF). First, a field experiment will quantify intra- and interspecific effects of fungal PSFs on germination-emergence and establishment. A companion greenhouse experiment will address questions about differences between field and lab-based PSF studies, and place this case study in the context of the current literature. Second, results from the field experiment will be incorporated in an existing, phenomenological multispecies population model, enabling comparisons of the overall stability of coexistence under a scenario in which only PSFs drive interactions at the recruitment stage, and a scenario including all possible sources of intra- and interspecific effects on recruitment. By combining field experiments, greenhouse studies, long-term demographic data, and models, this work will quantify the contribution of PSFs to the overall stability of coexistence in a sagebrush steppe community. This novel experimental and modeling framework can be extended to other communities and coexistence mechanisms in the future.