Spatial Heterogeneity in Soil Microbes Alters Outcomes of Plant Competition

Abstract

Plant species vary greatly in their responsiveness to nutritional soil mutualists, such as mycorrhizal fungi and rhizobia, and this responsiveness is associated with a trade-off in allocation to root structures for resource uptake. As a result, the outcome of plant competition can change with the density of mutualists, with microbe-responsive plant species having high competitive ability when mutualists are abundant and non-responsive plants having high competitive ability with low densities of mutualists. When responsive plant species also allow mutualists to grow to greater densities, changes in mutualist density can generate a positive feedback, reinforcing an initial advantage to either plant type. We study a model of mutualist-mediated competition to understand outcomes of plant-plant interactions within a patchy environment. We find that a microbe-responsive plant can exclude a non-responsive plant from some initial conditions, but it must do so across the landscape including in the microbe-free areas where it is a poorer competitor. Otherwise, the non-responsive plant will persist in both mutualist-free and mutualist-rich regions. We apply our general findings to two different biological scenarios: invasion of a non-responsive plant into an established microbe-responsive native population, and successional replacement of non-responders by microbe-responsive species. We find that resistance to invasion is greatest when seed dispersal by the native plant is modest and dispersal by the invader is greater. Nonetheless, a native plant that relies on microbial mutualists for competitive dominance may be particularly vulnerable to invasion because any disturbance that temporarily reduces its density or that of the mutualist creates a window for a non-responsive invader to establish dominance. We further find that the positive feedbacks from associations with beneficial soil microbes create resistance to successional turnover. Our theoretical results constitute an important first step toward developing a general understanding of the interplay between mutualism and competition in patchy landscapes, and generate qualitative predictions that may be tested in future empirical studies.

Effect of permafrost thaw on plant and soil fungal community in a boreal forest: Does fungal community change mediate plant productivity response?

“…This does not imply that the interactions between soil nutrients and the different fungal communities present at each site could not affect plant productivity. In fact, the strength of the mycorrhizal symbiosis is affected by changes in N and P (Abbott et al, ; Balzergue, Puech‐Pagès, Bécard, & Rochange, ; Breuillin et al, ; Nouri, Breuillin‐Sessoms, Feller, & Reinhardt, ), and future research is needed to test how soil nutrients and mycorrhizal community composition interact and shape plant community structure in boreal soils undergoing permafrost thaw.…”

Temporal carry‐over effects in sequential plant–soil feedbacks

“…Most plant–soil feedback experiments to date use only one phase of soil conditioning and these data have been the basis for models of PSF effects on plant community changes (Bonanomi et al , Eppinga et al , Fukami and Nakajima , Mack and Bever , Abbott et al ). As far as we are aware, only two experiments tested the effects of repeated conditioning by conspecifics (Mazzola , Packer and Clay ), and we are not aware of any sequential heterospecific feedback experiments.…”

Modelling nutritional mutualisms: challenges and opportunities for data integration

“…; Abbott et al . ). Furthermore, in plant‐microbe nutritional mutualisms characterised to date, spatially structured interactions lead to specialists interacting with subsets of generalists less frequently than expected by chance, which may be due to interspecific competition affecting the range of potential partners (Toju et al .…”

“…Abbott et al . ). These assumptions include both the exploratory and logistical assumptions that drive the construction of the model as well as the critical assumptions that the model is seeking to study (Servedio et al .…”

“…These models predict whether coexistence is feasible based on the availability of resources and nutritive demands of each species, thus providing an additional level of mechanistic detail that can be empirically measured (de Mazancourt & Schwartz 2010). Spatially structured interactions can be modelled through the use of dual-lattice structure (Parker 1999) or a patch environment (Abbott et al 2015). Under either mechanism, populations can interact based on dispersal distances and/or rates within a population dynamics model.…”