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

Utah State University, Logan UT

Investigators

Abstract

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.