Abstract

Ecosystems dominated by plants featuring ectomycorrhizae (EM) and arbuscular mycorrhizae (AM) promote distinct soil carbon dynamics. AM and EM soil environments can thus have different impacts on litter decomposition. However, current soil carbon models treat mycorrhizal impacts on the processes of soil carbon transformation as a black box. We re-formulated the soil carbon model Yasso15, and incorporated impacts of mycorrhizal vegetation on soil carbon pools of different recalcitrance. We examined alternative conceptualizations of mycorrhizal impacts on transformations of labile and stable carbon, and quantitatively assessed the performance of the selected optimal model in terms of the long-term fate of plant litter. We found that mycorrhizal impacts on pools of labile carbon in the litter are distinct from that on recalcitrant pools. Plant litter of the same chemical composition decomposes slower when exposed to EM-dominated ecosystems compared to AM-dominated ones, and across time, EM-dominated ecosystems accumulate more recalcitrant residues of non-decomposed litter. Overall, adding our mycorrhizal module into the Yasso model improved the accuracy of the temporal dynamics of carbon sequestration predictions. Our results suggest that mycorrhizal impacts on litter decomposition are underpinned by distinct decomposition pathways in AM- and EM-dominated ecosystems. Ignoring mycorrhiza-induced mechanisms will thus lead to an overestimation of climate impacts on decomposition dynamics. Our new model provides a benchmark for mechanistic and quantitative modelling of microbial impact on soil carbon. It helps to determine the relative importance of mycorrhizal associations and climate on organic matter decomposition rate and reduces the uncertainties in estimating soil carbon sequestration.

Highlights

  • IntroductionLong-term soil carbon sequestration is to a large extent determined by complex soil-plant rhizosphere and microbial 30 interactions (Dijkstra and Cheng, 2007; Fernandez and Kennedy, 2016; Fontaine et al, 2007; Ostle et al, 2009)

  • 10 Abstract Ecosystems dominated by plants featuring ectomycorrhizae (EM) and arbuscular mycorrhizae (AM) promote distinct soil carbon dynamics

  • Based on the RMSE, Akaike information criterion (AIC) and Bayesian information criterion (BIC), we selected Myco-Yasso 240 V2 as a model representing the optimal conceptualization of mycorrhizal impact on plant litter decomposition for later analysis

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Summary

Introduction

Long-term soil carbon sequestration is to a large extent determined by complex soil-plant rhizosphere and microbial 30 interactions (Dijkstra and Cheng, 2007; Fernandez and Kennedy, 2016; Fontaine et al, 2007; Ostle et al, 2009). These interactions contribute to atmospheric CO2 balance (Ostle et al, 2009; Todd-Brown et al, 2012) and are increasingly recognized as processes that counteract climate change (Terrer et al, 2016). Mycorrhizal fungi themselves are not capable of meaningfully obtaining carbon from decomposing plant litter (Bödeker et al, 2016; Lindahl and Tunlid, 2015). Instead, they receive carbon from their symbiotic host plants.

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