The next frontier of plant–soil feedback research: unraveling context dependence across biotic and abiotic gradients

Abstract

Question Plant–soil feedback (PSF) has emerged as a ubiquitous phenomenon and a potentially important predictor of plant community structure and dynamics. However, the predictive power of PSF in field contexts is mixed, and ecologists do not yet understand its relative importance compared to other factors that structure communities. Further progress requires a more nuanced understanding of how PSF interacts with other biotic and abiotic factors. Environmental factors (e.g. natural enemies, moisture, light, nutrients) are known to affect plant interactions with soil and soil organisms, leading to an expectation of environmental context dependence in plant–soil feedback. Such context dependence could explain when PSF is expected to be an important driver of community dynamics, and under what conditions PSF is likely to be positive (destabilizing) vs negative (stabilizing). Methods We conducted a literature review of studies that examined PSF across biotic and abiotic gradients. Results Although few relevant studies have been conducted in this emerging research area, results to date suggest that plant–soil feedback is sensitive to biotic factors, such as above‐ and below‐ground herbivory, and abiotic factors, such as nutrients and light. Conclusions We develop a conceptual framework to predict variation in the direction and strength of PSF depending on the biotic or abiotic drivers of feedback (e.g. pathogens, nutrients) and the environmental context (e.g. intensity of herbivory, soil fertility). We explore the utility of our predictive framework through discussion of case studies from the literature on context dependence in PSF. We also consider how different experimental approaches might yield different insights about PSF–environment interactions, and suggest key future research directions.

Plant–microbial interactions facilitate grassland species coexistence at the community level

“…Our experiment indicates soil nutrient availability did not significantly affect the magnitude of negative PMIs for graminoids. This is in agree with Smith‐Ramesh and Reynolds ().…”

“…Our findings suggest the magnitude and direction of these interactions were not altered by interspecific competition at the plant community level. Microbial influences on plant growth can be altered experimentally by manipulating light (Smith and Reynolds , Pfennigwerth et al ), nutrient availability (Gustafson and Casper , Manning et al ), temperature (Olsen et al ), and other environmental factors (Smith‐Ramesh and Reynolds ) which may also influence plant interspecific competition. Most previous experiments aimed to determine the influence of one specific environmental factor on plant–soil feedbacks.…”

Why are plant–soil feedbacks so unpredictable, and what to do about it?

“…There are numerous additional external drivers of PSF that are beyond the scope of this paper (Box ). However, the factors examined in detail here are known drivers of plant and soil organism performance and the ecosystem processes (e.g., nutrient cycling, productivity, carbon sequestration) they drive and hence would be expected to be important drivers of PSFs (Andriuzzi & Wall, ; Blankinship, Niklaus, & Hungate, ; Smith‐Ramesh & Reynolds, ). We selected these drivers because they are ubiquitous across ecosystems and are strongly associated with pressing ecological concerns (e.g., climate change, sustainable management of soils, trophic cascades), and the substantial research conducted to date allowed us to make robust predictions about how they might drive PSFs under different scenarios.…”

“…For example, combing new experimental work alongside data that have already been collected on plant community composition across these networks could allow us to follow back plant species’ abundance over time, thereby potentially identifying key drivers of PSFs retroactively, once the mechanisms are better understood. Executing PSF experiments across gradients has been proposed previously (Smith‐Ramesh & Reynolds, ), but not with explicit exploration of external drivers; and (5) Finally, using the global data collected to develop ecological mathematical models (e.g., biogeochemical models) will allow us to scale up our findings and make robust, comprehensive predictions about how the drivers of PSF will influence ecosystem processes (e.g., plant community composition shifts, decomposition, formation of soil organic matter, nutrient cycling) at larger, ecologically meaningful spatial and temporal scales. The stepwise procedure highlighted here can be systematically and continuously applied to design more predictive PSF experiments (Figure ).…”

When and where plant‐soil feedback may promote plant coexistence: a meta‐analysis

“…Even when feedback is negative, there is considerable variation in feedback’s strength, which has been linked to species abundance distributions (Klironomos ; Mangan et al ; Johnson et al ) and plant succession (Kardol et al ; Kulmatiski et al ; Bauer et al ). Despite the importance of variation in PSF’s strength and direction for determining plant coexistence and community dynamics, the factors that determine this variation remain largely unknown (Bever et al ; Smith‐Ramesh & Reynolds ).…”