Chemical changes in organic matter after fungal colonization in a nitrogen fertilized and unfertilized Norway spruce forest

César Nicolás,Adam Bahr,Håkan Wallander,Per Persson,Anders Tunlid,Sharon E Bone,John R Bargar,Juan P Almeida,Nicholas P Rosenstock,Magnus Ellström

doi:10.1007/s11104-017-3324-8

César Nicolás, Adam Bahr + Show 8 more

Open Access

https://doi.org/10.1007/s11104-017-3324-8

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Abstract

Background and aimsDecomposition and transformation of organic matter (OM) in forest soils are conducted by the concomitant action of saprotrophic and mycorrhizal fungi. Here, we examine chemical changes in OM after fungal colonization in nitrogen fertilized and unfertilized soils from a Norway spruce forest.MethodsSand-filled bags amended with composted maize leaves were placed in the forest soil and harvested after 17 months. Infrared and near edge X-ray absorption fine structure spectroscopies were used to study the chemical changes in the OM. Fungal community composition of the bags was also evaluated.ResultsThe proportion of ectomycorrhizal fungi declined in the fertilized plots, but the overall fungal community composition was similar between N treatments. Decomposition of the OM was, independently of the N level or soil horizon, accompanied by an increase of C/N ratio of the mesh-bag content. Moreover, the proportions of carboxylic compounds in the incubated OM increased in the mineral horizon, while heterocyclic-N compounds decreased, especially in unfertilized plots with higher N demand from the trees.ConclusionsOur results indicate that more oxidized organic C and less heterocyclic-N proportions in the OM remain after fungal colonization in the mineral layers, and suggest that ectomycorrhizal fungi transfer less heterocyclic-N from the mesh bags to the host trees under high N levels.

Highlights

Saprotrophic fungi are one of the major decomposers of organic matter (OM) in boreal and northern temperate forests
The proportion of ectomycorrhizal fungi declined in the fertilized plots, but the overall fungal community composition was similar between N treatments
Our results indicate that more oxidized organic C and less heterocyclic-N proportions in the OM remain after fungal colonization in the mineral layers, and suggest that ectomycorrhizal fungi transfer less heterocyclic-N from the mesh bags to the host trees under high N levels

Summary

Introduction

Saprotrophic fungi are one of the major decomposers of organic matter (OM) in boreal and northern temperate forests. These microorganisms harbour a wide range of hydrolytic and oxidative enzymes such as cellobiohydrolases, laccases, peroxidases or lytic polysaccharide mono-oxygenases that allow them to break down plant litter (Baldrian 2006; Bugg et al 2011; Hemsworth et al 2013; Kohler et al 2015) and use it as a C source. Recent studies have shown that ECM fungi have retained similar oxidative capacity as saprotrophic fungi (Shah et al 2016) This oxidative capacity has been suggested to primarily assist the ECM fungi to mobilizing nutrients from soil OM such as N embedded in the soil organic complexes, rather than to obtain C from the soil OM (Lindahl and Tunlid 2015; Shah et al 2016).

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