Shifts in the Abundances of Saprotrophic and Ectomycorrhizal Fungi With Altered Leaf Litter Inputs.

Sara Marañón-Jiménez,Marion Schrumpf,Matthias Cuntz,Corinna Rebmann,Erik Verbruggen,Dajana Radujković,Josep Peñuelas,Oriol Grau,Andreas Richter

doi:10.3389/fpls.2021.682142

Abstract

Ectomycorrhizal (EcM) and saprotrophic fungi interact in the breakdown of organic matter, but the mechanisms underlying the EcM role on organic matter decomposition are not totally clear. We hypothesized that the ecological relations between EcM and saprotroph fungi are modulated by resources availability and accessibility, determining decomposition rates. We manipulated the amount of leaf litter inputs (No-Litter, Control Litter, Doubled Litter) on Trenched (root exclusion) and Non-Trenched plots (with roots) in a temperate deciduous forest of EcM-associated trees. Resultant shifts in soil fungal communities were determined by phospholipid fatty acids and DNA sequencing after 3 years, and CO2 fluxes were measured throughout this period. Different levels of leaf litter inputs generated a gradient of organic substrate availability and accessibility, altering the composition and ecological relations between EcM and saprotroph fungal communities. EcM fungi dominated at low levels of fresh organic substrates and lower organic matter quality, where short-distances exploration types seem to be better competitors, whereas saprotrophs and longer exploration types of EcM fungi tended to dominate at high levels of leaf litter inputs, where labile organic substrates were easily accessible. We were, however, not able to detect unequivocal signs of competition between these fungal groups for common resources. These results point to the relevance of substrate quality and availability as key factors determining the role of EcM and saprotroph fungi on litter and soil organic matter decay and represent a path forward on the capacity of organic matter decomposition of different exploration types of EcM fungi.

Highlights

Plants adjust the amount of carbon (C) invested in abovevs. belowground parts in response to soil nutrient availability to optimize biomass returns of invested carbon (Shipley and Meziane, 2002; Dybzinski et al, 2011)
We investigated the similarity of the soil fungal communities amongst root and leaf litter inputs treatments by non-metric multidimensional scaling (NMDS) ordinations with the readabundance data using the Bray–Curtis index (“BiodiversityR” package; Kindt and Coe, 2005)
Our results show the proliferation of saprotrophs and EcM fungi of different exploration types based on their acquisition strategies and the available target substrates

Summary

Introduction

Plants adjust the amount of carbon (C) invested in abovevs. belowground parts in response to soil nutrient availability to optimize biomass returns of invested carbon (Shipley and Meziane, 2002; Dybzinski et al, 2011). EcM fungi may compete with the saprotrophic community for limiting water, nutrients or space (Lindahl et al, 2001; Koide and Wu, 2003; Bödeker et al, 2016). This competition has been long hypothesized to slow down decomposition rates (i.e., “Gadgil effect,” Gadgil and Gadgil, 1971, 1975), leading to the prediction of larger C storage in forest soils (Orwin et al, 2011; Averill et al, 2014). EcM fungi have shown both no effect (Mayor and Henkel, 2006; but see McGuire et al, 2010) and a stimulation of decomposition rates (Entry et al, 1991; Zhu and Ehrenfeld, 1996; Brzostek et al, 2015) and the mechanisms underlying the EcM role on organic matter decomposition are not totally clear (Fernandez and Kennedy, 2015)

Methods

Results

Discussion

Conclusion