Nitrogen addition increases the contents of glomalin-related soil protein and soil organic carbon but retains aggregate stability in a Pinus tabulaeformis forest.

Lipeng Sun,Hang Jing,Guoliang Wang,Guobin Liu

doi:10.7717/peerj.5039

Abstract

BackgroundGlomalin-related soil protein (GRSP) and soil organic carbon (SOC) contribute to the formation and stability of soil aggregates, but the mechanism by which global atmospheric nitrogen (N) deposition changes soil aggregate stability by altering the distribution of GRSP and SOC in different aggregate fractions remains unknown.MethodsWe used a gradient N addition (0–9 g N m−2 y−1) in Pinus tabulaeformis forest for two years in northeast China and then examined the changes in SOC contents, total GRSP (T-GRSP), and easily extractable GRSP (EE-GRSP) contents in three soil aggregate fractions (macro-aggregate: >250 μm, micro-aggregate: 250–53 μm, and fine material: <53 μm) and their relationship with aggregate stability.Results(1) The soil was dominated by macro-aggregates. Short term N addition had no significant effect on mean weight diameter (MWD) and geometric mean diameter (GMD). (2) GRSP varied among aggregate fractions, and N addition had different effects on the distribution of GRSP in aggregate fractions. The EE-GRSP content in the macro-aggregates increased initially and then decreased with increasing N addition levels, having a peak value of 0.480 mg g−1 at 6 g N m−2 y−1. The micro-aggregates had the lowest EE-GRSP content (0.148 mg g−1) at 6 g N m−2 y−1. Furthermore, the T-GRSP content significantly increased in the aggregate fractions with the N addition levels. (3) The macro-aggregate had the highest SOC content, followed by the micro-aggregate and the fine material had the lowest SOC content. N addition significantly increased the SOC content in all the aggregate fractions. (4) GRSP and SOC contents were not significantly correlated with MWD.ConclusionGlomalin-related soil protein and SOC contents increased by N addition, but this increase did not enhance aggregate stability in short term, and the improvement of stability might depend on binding agents and incubation time.

Highlights

Human activities have led to a rapid increase in global nitrogen (N) deposition (Dirnbock et al, 2017)
Glomalin-related soil protein and soil organic carbon (SOC) contents increased by N addition, but this increase did not enhance aggregate stability in short term, and the improvement of stability might depend on binding agents and incubation time
We proposed that N addition significantly increases SOC content in fine materials and minimal affect SOC content in other size aggregate fractions

Summary

Introduction

Human activities have led to a rapid increase in global nitrogen (N) deposition (Dirnbock et al, 2017). Some researchers found that N addition significantly increased GRSP content in bulk soil (Zhang et al, 2015; Garcia et al, 2008), but Wuest et al (2005) found that N addition had no significant effects on GRSP content in bulk soil These inconsistent results may be related to the soil initial N content (Treseder, Turner & Mack, 2007), as well as N addition level and duration (Garcia et al, 2008; Treseder, 2004). Conclusion: Glomalin-related soil protein and SOC contents increased by N addition, but this increase did not enhance aggregate stability in short term, and the improvement of stability might depend on binding agents and incubation time

Methods

Results

Discussion

Conclusion