Using root economics traits to predict biotic plant soil-feedbacks

Abstract

Plant-soil feedbacks have been recognised as playing a key role in a range of ecological processes, including succession, invasion, species coexistence and population dynamics. However, there is substantial variation between species in the strength of plant-soil feedbacks and predicting this variation remains challenging. Here, we propose an original concept to predict the outcome of plant-soil feedbacks. We hypothesize that plants with different combinations of root traits culture different proportions of pathogens and mutualists in their soils and that this contributes to differences in performance between home soils (cultured by conspecifics) versus away soils (cultured by heterospecifics). We use the recently described root economics space, which identifies two gradients in root traits. A conservation gradient distinguishes fast vs. slow species, and from growth defence theory we predict that these species culture different amounts of pathogens in their soils. A collaboration gradient distinguishes species that associate with mycorrhizae to outsource soil nutrient acquisition vs. those which use a “do it yourself” strategy and capture nutrients without relying strongly on mycorrhizae. We provide a framework, which predicts that the strength and direction of the biotic feedback between a pair of species is determined by the dissimilarity between them along each axis of the root economics space. We then use data from two case studies to show how to apply the framework, by analysing the response of plant-soil feedbacks to measures of distance and position along each axis and find some support for our predictions. Finally, we highlight further areas where our framework could be developed and propose study designs that would help to fill current research gaps.

A trait‐based framework linking the soil metabolome to plant–soil feedbacks

“…Additional manipulation of the soil biota may provide important insights about the direct and indirect effects of the soil metabolome in mediating plant–soil interactions. These PSF experiments would be ideal to test the trait‐based framework described in this paper, as well as to test the extent to which greater phylogenetic or functional distance between a focal species and a species that produces the soil chemical legacy lead to stronger PSF effects (Semchenko et al ., 2022; Rutten & Allan, 2023).…”

“…better performance in live conspecific soil than in sterilised control). The potential for PSF to modulate species coexistence via species‐specific microbial legacies is further predicted to depend on the distance between co‐occurring species in functional trait space, with stronger feedbacks occurring among species with more contrasting trait values (Semchenko et al ., 2022; Rutten & Allan, 2023). These predictions are generally supported by several empirical studies (Lemmermeyer et al ., 2015; Fitzpatrick et al ., 2017; Kulmatiski et al ., 2017; Lekberg et al ., 2018; Xi et al ., 2021), although the strength of trait–PSF relationships varies between studies (Bukowski et al ., 2018; Heinen et al ., 2018) and evidence for root economic traits remains limited (Cortois et al ., 2016; Semchenko et al ., 2018; Spitzer et al ., 2022).…”

Plant-soil feedback: the next generation

“…This could partly be due to many experiments being conducted under highly-controlled settings that do not consider a range of other important factors present under natural conditions. For example, Rutten and Allan (2023) proposed a framework aiming to enhance the predictability of the direction and strength of plant-soil feedback effects by incorporating root trait gradients of the root economics spectrum (i.e., 'conservation' and 'collaboration' gradients) and their interactions. Next, using data from two previous plant-soil feedback studies, Rutten and Allan (2023) demonstrated that their framework could substantially explain plant-soil feedback between species.…”

Between‐ versus within‐species variation in plant–soil feedback relates to different functional traits, but exudate variability is involved at both scales

“…Several studies investigated the potential for principal gradients of functional trait variations to predict PSF (Cortois et al., 2016; Rutten & Allan, 2023; Semchenko et al., 2022). Two principal gradients associating with PSF have emerged: the conservation gradient and the collaboration gradient (Bergmann et al., 2020).…”