Using root economics traits to predict 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 root traits culture different proportions of pathogens and mutualists and 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 spectrum, which identifies two gradients in root traits. A conservation gradient distinguishes fast vs. slow species, and from the 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 mycorrhizae. We provide a framework, which predicts that the strength and direction of feedback between a pair of species is determined by the functional distance between them along each axis. 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 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.

Contrasted root trait responses between saplings of an arbuscular and an ectomycorrhizal tree species in open field compared to forest conditions

“…Plants show plastic trait responses to many shifts in environmental conditions (Fransen et al, 1998; Gratani, 2014; Tobner et al, 2013; Valverde‐Barrantes et al, 2013; Weemstra et al, 2020), and especially to variations in soil nutrient levels (Adams et al, 2013; Cahill & McNickle, 2011) and spatial distribution (Cahill et al, 2010; Drew, 1975; Hodge, 2004). It is generally assumed that soil microbes mediate species root traits (Baxendale et al, 2014; Cortois et al, 2016; Rutten & Allan, 2022; Rutten & Gómez‐Aparicio, 2018) and play key role in ecological succession, species invasion or communities dynamics (Mack et al, 2019; Mohan et al, 2014; Pausas & Bond, 2022; Rigg et al, 2016). However, it is difficult to capture such plastic plant trait responses and disentangle the signals from mycorrhizal symbiont availability or soil fertility.…”