Nitrogen enrichment impacts on boreal litter decomposition are driven by changes in soil microbiota rather than litter quality

Nadia I Maaroufi,Annika Nordin,Kristin Palmqvist,Michael J Gundale

doi:10.1038/s41598-017-04523-w

Abstract

In nitrogen (N) limited boreal forests, N enrichment can impact litter decomposition by affecting litter quality and by changing the soil environment where litter decomposes. We investigated the importance of litter quality and soil factors on litter decomposition using a 2-year reciprocal transplant experiment for Picea abies needle litter, derived from plots subjected to 17 years of N addition, including control, low and high N treatments (ambient, 12.5 and 50 kg N ha−1 yr−1, respectively). Our data show that changes in soil factors were the main pathway through which N impacted litter decomposition, with rates reduced by ~15% when placed in high N relative to control plots, regardless of litter origin. Litter decomposition was correlated to soil microbiota, with Picea abies litter decomposition positively correlated with gram negative and fungal functional groups. Our results suggest that previous findings of increase soil C accumulation in response to N deposition is likely to occur as a result of changes in soil microbiota rather than altered litter quality.

Highlights

Anthropogenic activities have increased global emissions of reactive nitrogen (Nr), which have resulted in higher rates of atmospheric Nr deposition[1]
The litter decomposition significantly declined by ~15% and non-significantly declined by ~7% when located in the high N (50 kg N ha−1 yr−1) and low N (12.5 kg N ha−1 yr−1) plots relative to the control plots, respectively, regardless of the litter origin (Fig. 1a; Table 1)
Variation partitioning analysis showed that the variation of litter decomposed in the control plots was mainly explained by fungal (24–34%) and actinomycetes (4–26%) phospholipid fatty acids method (PLFA) biomasses, as well as the litter’s % lignin (0–18%) and % cellulose (13–24%) (Fig. 2)

Summary

Introduction

Anthropogenic activities have increased global emissions of reactive nitrogen (Nr), which have resulted in higher rates of atmospheric Nr deposition[1]. We tested the following hypotheses: (i) That potential changes in litter quality caused by N enrichment will lead to reduced decomposition rates of the most abundant evergreen species (P. abies) in our study system, and (ii) that N enrichment caused changes in soil biota (e.g. reduced total and fungal biomasses) will lead to reduced decomposition rates. By testing these hypotheses together, our study provides a rare opportunity to separate the relative effect of two pathway mechanisms that have been proposed to influence soil C accumulation in N limited northern forest environments[2, 4]

Objectives

Methods

Results

Conclusion