Ten years of elevated CO2 affects soil greenhouse gas fluxes in an open top chamber experiment

Abstract

The production and consumption of greenhouse gases (GHGs) in soils are largely regulated by biological processes. Increasing atmospheric CO2 may alter these processes, thereby affecting GHG emissions and their feedbacks to climate. Here, we used an open top chamber (OTC) experiment to examine the effects of elevated CO2 for ten years on soil GHG fluxes in a Quercus mongolica dominated system in northeastern China. Our results showed that elevated CO2 increased soil CO2 emissions, consistent with increased microbial biomass and the abundance of arbuscular mycorrhizal fungi and actinomycetes. Additionally, elevated CO2 increased CH4 uptake due to stimulated growth of methanotrophs. The seasonal mean soil N2O flux was not changed by elevated CO2, consistent with unchanged ammonia oxidizing bacteria, archaea and denitrifiers, which was probably due to large variations between the individual OTCs and with time. However, seasonal cumulative soil N2O emissions increased by 64.7% under elevated CO2. Our results also hinted that nitrification by ammonia oxidizing archaea was the major process of soil N2O emissions. In our study elevated CO2 increased soil GHG emissions and the cumulative global warming potential by 27.8%, causing an important positive feedback to climate change.