A quantitative synthesis of soil microbial effects on plant species coexistence

Abstract

Soil microorganisms play a major role in shaping plant diversity, not only through their direct effects as pathogens, mutualists, and decomposers, but also by altering interactions between plants. In particular, previous research has shown that the soil community often generates frequency-dependent feedback loops among plants that can either destabilize species interactions, or generate stabilizing niche differences that promote species coexistence. However, recent insights from modern coexistence theory have shown that microbial effects on plant coexistence depend not only on these stabilizing or destabilizing effects, but also on the degree to which they generate competitive fitness differences. While many previous experiments have generated the data necessary for evaluating microbially mediated fitness differences, these effects have rarely been quantified in the literature. Here we present a meta-analysis of data from 50 studies, which we used to quantify the microbially mediated (de)stabilization and fitness differences derived from a classic plant-soil feedback model. Across 518 pairwise comparisons, we found that soil microbes generated both stabilization (or destabilization) and fitness differences, but also that the microbially mediated fitness differences dominated. As a consequence, if plants are otherwise equivalent competitors, the balance of soil microbe-generated (de)stabilization and fitness differences drives species exclusion much more frequently than coexistence or priority effects. Our work shows that microbially mediated fitness differences are an important but overlooked effect of soil microbes on plant coexistence. This finding paves the way for a more complete understanding of the processes that maintain plant biodiversity.

A quantitative synthesis of soil microbial effects on plant species coexistence

“…The compiled meta-dataset and all analysis code have been deposited at https://doi.org/10.5281/zenodo.6513066 ( 99 ).…”

Mycorrhizal nutrient acquisition strategies shape tree competition and coexistence dynamics

“…Microbial effects can be quantified by comparing interaction coefficients calculated from competition treatments using either Live or Sterilized soils of species j . Here, we quantify microbial effects using plant performance in sterilized soil as a reference, thereby capturing the overall impact of soil microbes (see also recent discussion on the usage of other reference soils such as unconditioned field soil, Abbott et al, 2021; Yan et al, 2022). Plant–plant interaction, in the presence of soil microbial effects, can be calculated as: and in the absence of microbial effects as:where B i , j ,live and B i , j ,sterilized represent the biomass of species i under the competitive impact of species j in Live and Sterilized inoculum of soil j , respectively, B i ,0,sterilized represents the biomass of species i grown individually in Sterilized inoculum, and Δ N j represents the density of species j competitors (in this case, Δ N j = 1).…”

“…Microbial effects can be quantified by comparing interaction coefficients calculated from competition treatments using either Live or Sterilized soils of species j. Here, we quantify microbial effects using plant performance in sterilized soil as a reference, thereby capturing the overall impact of soil microbes (see also recent discussion on the usage of other reference soils such as unconditioned field soil, Abbott et al, 2021;Yan et al, 2022). Plant-plant interaction, in the presence of soil microbial effects, can be calculated as: and in the absence of microbial effects as:…”