Decomposing litter and associated microbial activity responses to nitrogen deposition in two subtropical forests containing nitrogen-fixing or non-nitrogen-fixing tree species

Guixiang Zhou,Xiaofeng Xu,Jiabao Zhang,Xiuwen Qiu,Feng Wei

doi:10.1038/s41598-018-30666-5

Abstract

Atmospheric nitrogen (N) deposition has caused concern due to its effects on litter decomposition in subtropical regions where N-fixing tree species are widespread. However, the effect of N deposition on litter decomposition in N-fixing plantations remains unclear. We investigated the effects of a 2-year N deposition treatment on litter decomposition, microbial activity, and nutrient release in two subtropical forests containing Alnus cremastogyne (AC, N-fixing) and Liquidambar formosana (LF, non-N-fixing). The decomposition rate in AC was faster than in LF when there was no experimental N deposition. In AC, the initial decomposition rate was faster when additional N was applied and was strongly linked to higher cellulose-degrading enzyme activities during the early decomposition stage. However, N deposition reduced litter decomposition and inhibited lignin-degrading enzyme activities during the later decomposition stage. Nitrogen deposition enhanced carbohydrate and alcohol utilization, but suppressed amino acid and carboxylic acid uptake in the AC plantation. However, it did not significantly affect litter decomposition and microbial activity in the LF plantation. In conclusion, N deposition could inhibit litter decomposition by changing microbial enzyme and metabolic activities during the decomposition process and would increase carbon accumulation and nitrogen retention in subtropical forests with N-fixing tree species.

Highlights

Litter decomposition is a critically fundamental process that affects nutrient cycles and carbon (C) storage in ecosystems[1]
This study reports the effects of simulated N deposition on the litter decomposition rate, nutrient release by the litter, and the enzyme and metabolic activities of decomposers in two subtropical plantations containing Alnus cremastogyne (AC, N-fixing tree species) or Liquidambar formosana (LF, non-N-fixing tree species) in China
Over the 24-month decomposition period, N deposition initially speeded up litter decomposition, but the decomposition rate was slower after N addition during the later stage in the A. cremastogyne (AC) plantation (Fig. 1)

Summary

Introduction

Litter decomposition is a critically fundamental process that affects nutrient cycles and carbon (C) storage in ecosystems[1]. Numerous reports have suggested that the activities of microbial enzymes associated with litter cellulose and lignin degradation are linked to litter decomposition rates in different ecosystems[10,14,15]. The effects of N addition on enzyme activities often varied across sites due to differences in nutrient availability[18], litter quality[10,19], and the composition of the microbial community[20] during the decomposition process. This study reports the effects of simulated N deposition on the litter decomposition rate, nutrient release by the litter, and the enzyme and metabolic activities of decomposers in two subtropical plantations containing Alnus cremastogyne (AC, N-fixing tree species) or Liquidambar formosana (LF, non-N-fixing tree species) in China. A 2-year experiment was conducted to test the following hypotheses: (1) N deposition would inhibit the decomposition rate of AC litter in the AC plantation and increase the decomposition rate of LF litter in the LF plantation; and (2) N addition would suppress the cellulose-degrading and oxidative enzymes in the AC plantation and enhance these enzymes in the LF plantation

Methods

Results

Conclusion