Minjie Xu

Responses of CO2 efflux from an alpine meadow soil on the Qinghai Tibetan Plateau to multi-form and low-level N addition

AimsTo assess the effects of atmospheric N deposition on the C budget of an alpine meadow ecosystem on the Qinghai–Tibetan Plateau, it is necessary to explore the responses of soil-atmosphere carbon dioxide (CO2) exchange to N addition.MethodsBased on a multi-form, low-level N addition experiment, soil CO2 effluxes were monitored weekly using the static chamber and gas chromatograph technique. Soil variables and aboveground biomass were measured monthly to examine the key driving factors of soil CO2 efflux.ResultsThe results showed that low-level N input tended to decrease soil moisture, whereas medium-level N input maintained soil moisture. Three-year N additions slightly increased soil inorganic N pools, especially the soil NH4+-N pool. N applications significantly increased aboveground biomass and soil CO2 efflux; moreover, this effect was more significant from NH4+-N than from NO3−-N fertilizer. In addition, the soil CO2 efflux was mainly driven by soil temperature, followed by aboveground biomass and NH4+-N pool.ConclusionsThese results suggest that chronic atmospheric N deposition will stimulate soil CO2 efflux in the alpine meadow on the Qinghai–Tibetan Plateau by increasing available N content and promoting plant growth.

Simulated Nitrogen Deposition Reduces CH4 Uptake and Increases N2O Emission from a Subtropical Plantation Forest Soil in Southern China

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.