Effects of Elevated CO2 and Nitrogen Deposition on Ecosystem Carbon Fluxes on the Sanjiang Plain Wetland in Northeast China

Jianbo Wang,Jifeng Wang,Tingcheng Zhu,Hongwei Ni,Haixiu Zhong,Xiaoling Fu,Ben Bond-Lamberty

doi:10.1371/journal.pone.0066563

Jianbo Wang, Jifeng Wang + Show 5 more

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https://doi.org/10.1371/journal.pone.0066563

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Abstract

BackgroundIncreasing atmospheric CO2 and nitrogen (N) deposition across the globe may affect ecosystem CO2 exchanges and ecosystem carbon cycles. Additionally, it remains unknown how increased N deposition and N addition will alter the effects of elevated CO2 on wetland ecosystem carbon fluxes.Methodology/Principal FindingsBeginning in 2010, a paired, nested manipulative experimental design was used in a temperate wetland of northeastern China. The primary factor was elevated CO2, accomplished using Open Top Chambers, and N supplied as NH4NO3 was the secondary factor. Gross primary productivity (GPP) was higher than ecosystem respiration (ER), leading to net carbon uptake (measured by net ecosystem CO2 exchange, or NEE) in all four treatments over the growing season. However, their magnitude had interannual variations, which coincided with air temperature in the early growing season, with the soil temperature and with the vegetation cover. Elevated CO2 significantly enhanced GPP and ER but overall reduced NEE because the stimulation caused by the elevated CO2 had a greater impact on ER than on GPP. The addition of N stimulated ecosystem C fluxes in both years and ameliorated the negative impact of elevated CO2 on NEE.Conclusion/SignificanceIn this ecosystem, future elevated CO2 may favor carbon sequestration when coupled with increasing nitrogen deposition.

Highlights

Atmospheric CO2 concentrations are predicted to double by the end of the century [1]
We examined soil microclimate (Tsoil and soil water content) and ecosystem C fluxes (NEE, ecosystem respiration (ER) and Gross primary productivity (GPP)) results for the entire 2010–2011 period and used repeated measures of ANOVAs to test for main effects and interactions, and whether these changed over time
The seasonal dynamics of ecosystem carbon uxes observed in this study were high in mid-summer and low in the early and late growing seasons, which reected air temperature (Fig. 1, 2)

Summary

Introduction

Atmospheric CO2 concentrations are predicted to double by the end of the century [1]. Different ecosystem respiration responses to N addition have been reported in previous studies, including increases [10,11,12], decreases [13,14] and no significant changes [15]. It remains unclear whether N deposition leads to net ecosystem C sequestration [16,17]. Increasing atmospheric CO2 and nitrogen (N) deposition across the globe may affect ecosystem CO2 exchanges and ecosystem carbon cycles. It remains unknown how increased N deposition and N addition will alter the effects of elevated CO2 on wetland ecosystem carbon fluxes

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