Plant‐derived compounds to improve soil inoculation for restoration

Abstract

Restoring the soil microbiome is increasingly recognized as an important requirement for the success of ecosystem restoration. Soil inoculation can reintroduce the missing taxa, but its application is limited by the large amount of donor soil that is needed and by the poor persistence of the inoculants, because of habitat filtering, priority effects and the loss of plant–microbe feedbacks. Here we propose the metabolite‐inoculum approach, a framework that combines the chemical diversity of plants with soil inoculation, in order to improve the establishment, persistence and effectiveness of introduced microbial communities. In this framework, the chemical input is delivered as fresh and dead plant material, as extracts of this material or as purified compounds that are applied together with the inoculum, and not by adding or manipulating the living plant community. We first synthesize the evidence that plant metabolites, from both above‐ and below‐ground tissues, act as selective regulators of soil microbial composition and diversity. Building on this, we propose a framework for the selection of plant materials and metabolites at the species, tissue and compound levels, and we introduce the parallel concepts of core and keystone metabolites that are matched to their corresponding microbial groups. We then identify the main challenges of the approach, the mismatch in timescale, the non‐target effects and the feasibility, and we translate them into testable hypotheses. Finally, we discuss the contexts in which the approach is likely to work and the contexts in which it is not. In this way, we frame the metabolite‐inoculum approach as a research agenda through bridging chemical ecology and microbial ecology, offering a potential solution to reduce dependency on donor soil, improve inoculant effectiveness and accelerate the recovery of degraded soils toward desired ecosystem states. Read the free Plain Language Summary for this article on the Journal blog.