Effects of soil microbes on plant competition: a perspective from modern coexistence theory

Abstract

ETH Z€ urich, 8092 Z€ urich, Switzerland Citation: Ke, P.-J., and J. Wan. 2020. Effects of soil microbes on plant competition: a perspective from modern coexistence theory. Ecological Monographs 90(1):Abstract. Growing evidence shows that soil microbes affect plant coexistence in a variety of systems. However, since these systems vary in the impacts microbes have on plants and in the ways plants compete with each other, it is challenging to integrate results into a general predictive theory. To this end, we suggest that the concepts of niche and fitness difference from modern coexistence theory should be used to contextualize how soil microbes contribute to plant coexistence. Synthesizing a range of mechanisms under a general plant-soil microbe interaction model, we show that, depending on host specificity, both pathogens and mutualists can affect the niche difference between competing plants. However, we emphasize the need to also consider the effect of soil microbes on plant fitness differences, a role often overlooked when examining their role in plant coexistence. Additionally, since our framework predicts that soil microbes modify the importance of plant-plant competition relative to other factors for determining the outcome of competition, we suggest that experimental work should simultaneously quantify microbial effects and plant competition. Thus, we propose experimental designs that efficiently measure both processes and show how our framework can be applied to identify the underlying drivers of coexistence. Using an empirical case study, we demonstrate that the processes driving coexistence can be counterintuitive, and that our general predictive framework provides a better way to identify the true processes through which soil microbes affect coexistence.

The analysis of plant root responses to nutrient concentration, soil volume and neighbour presence: Different statistical approaches reflect different underlying basic questions

“…Meanwhile, we should also make sure that a proper design for a specific component effect should also help to eliminate or at least minimize the impacts from other confounding (or unwanted) effects. Since the methodologies for studying the effects of allelopathy (Inderjit & Callaway, 2003) and mediations from soil microbes (Hoeksema, 2015; Ke & Wan, 2020) have been well established, here we only focus on the other two, which are also the main interests in the current study.…”

Quantifying microbially mediated fitness differences reveals the tendency for plant-soil feedbacks to drive species exclusion among California annual plants

“…Theoretical and empirical studies have shown that plant-soil feedbacks can influence whether a pair of species coexist if they drive stabilizing feedback loops that favor species that fall to low abundance and disadvantage more abundant species (or destabilizing loops that favor more abundant species and disadvantage rare ones) (Bever et al 1997, Crawford et al 2019). However, recent theoretical advances have clarified that species coexistence is also determined by the degree to which soil micobes mediate an average fitness difference that gives one species a demographic advantage over its competitor, regardless of its abundance in the system (Chesson 2000, Kandlikar et al 2019, Ke and Wan 2019). Here, we show that empirically quantifying the microbially mediated fitness difference and comparing it to the degree of microbial stabilization in Bever et al (1997)’s classic model of plant-soil feedback is essential for understanding how soil microbes shape plant species coexistence.…”

Natural Enemies and the Maintenance of Tropical Tree Diversity: Recent Insights and Implications for the Future of Biodiversity in a Changing World

“…Many factors produce both effects (Song et al, 2019). In particular, Janzen-Connell effects produce a stabilizing mechanism; however, they can also produce competitive differences if species are differently susceptible to their natural enemies (Stump & Comita, 2018;Ke & Wan, 2019;Kandlikar et al, 2019), or if enemy spillover is occurring (Stump, 2017). Thus, a more modern view of the Janzen-Connell hypothesis is that Janzen-Connell effects are a factor producing stabilizing mechanisms-likely one of manyand that they can allow coexistence if they are stronger than any competitive differences in the community.…”

“…4). Differential susceptibility also produces competitive differences (Stump & Comita, 2018;Ke & Wan, 2019;Kandlikar et al, 2019): if a species is highly susceptible to its natural enemies, and most seeds of that species are unable to disperse away from those enemies, then that species will be at a disadvantage compared to species that can tolerate their natural enemies (Stump & Comita, 2018) (Fig. 4).…”