Simulated nitrogen deposition reduces CH4 uptake and increases N2O emission from a subtropical plantation forest soil in southern China.

Xusheng Dang,Huajun Fang,Shulan Cheng,Minjie Xu,Linsen Li,Lei Wang,Guirui Yu,Yongsheng Wang

doi:10.1371/journal.pone.0093571

Abstract

To date, few studies are conducted to quantify the effects of reduced ammonium (NH4 +) and oxidized nitrate (NO3 −) on soil CH4 uptake and N2O emission in the subtropical forests. In this study, NH4Cl and NaNO3 fertilizers were applied at three rates: 0, 40 and 120 kg N ha−1 yr−1. Soil CH4 and N2O fluxes were determined twice a week using the static chamber technique and gas chromatography. Soil temperature and moisture were simultaneously measured. Soil dissolved N concentration in 0–20 cm depth was measured weekly to examine the regulation to soil CH4 and N2O fluxes. Our results showed that one year of N addition did not affect soil temperature, soil moisture, soil total dissolved N (TDN) and NH4 +-N concentrations, but high levels of applied NH4Cl and NaNO3 fertilizers significantly increased soil NO3 −-N concentration by 124% and 157%, respectively. Nitrogen addition tended to inhibit soil CH4 uptake, but significantly promoted soil N2O emission by 403% to 762%. Furthermore, NH4 +-N fertilizer application had a stronger inhibition to soil CH4 uptake and a stronger promotion to soil N2O emission than NO3 −-N application. Also, both soil CH4 and N2O fluxes were driven by soil temperature and moisture, but soil inorganic N availability was a key integrator of soil CH4 uptake and N2O emission. These results suggest that the subtropical plantation soil sensitively responses to atmospheric N deposition, and inorganic N rather than organic N is the regulator to soil CH4 uptake and N2O emission.

Highlights

Humid tropical biome stores approximately 10% of global soil carbon (C) [1] and plays a vital role in the budget of ecosystem C and nitrogen (N) fluxes
This study emphasizes the contrasting effects of oxidized NO32 and reduced NH4+ inputs on the fluxes of CH4 uptake and N2O emission from a subtropical plantation soil based on high frequency observations
We found that N addition tended to inhibit soil CH4 uptake, and dramatically promoted soil N2O emission

Summary

Introduction

Humid tropical biome stores approximately 10% of global soil carbon (C) [1] and plays a vital role in the budget of ecosystem C and nitrogen (N) fluxes. The amount of nitrous oxide (N2O) emission from the subtropical and tropical forest soils is estimated at 0.9–3.6 T g yr, accounting for 14% to 23% of the global N2O budget [2]. Well-aerated soils in the subtropical and tropical forests potentially function as a significant sink of atmospheric methane (CH4) during the dry season [3,4,5,6]. The uptake of CH4 from the subtropical and tropical forest soils is estimated to be 6.2 T g yr, accounting for 28% of the global CH4 sink [7]. The importance of the subtropical and tropical forest soils as atmospheric CH4 sink and N2O source is well understood, few observations can be available in this region [8,9,10]. Low-frequency measurement of gas fluxes in the few studies is unable to accurately estimate the annual amount of soil CH4 uptake and N2O emission, which leads to a high uncertainty in the budget of global soil CH4 and N2O fluxes

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Conclusion