Yongsheng Wang

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.

Nitrous oxide and methane emissions during rice growth and through rice plants: effect of dicyandiamide and hydroquinone

Abstract. There is growing interest in N2O and CH4 transport through rice plants, but very little information is available on the effects of inhibitors on these gaseous emissions during rice growth and through rice plants. The closed chamber technique was used to study the effect of the urease inhibitor hydroquinone (HQ) and the nitrification inhibitor dicyandiamide (DCD) on N2O and CH4 emissions. As rice plants grew, the N2O emission through rice plants was significantly reduced in all treatments; N2O emissions were always lower in the presence than in the absence of inhibitor(s). These variations paralleled those in NO3–-N content of fresh rice plants. During the rice growth period, increasing NO3–-N content in rice plants paralleled the increase in the N2O emission through rice plants. Hence, NO3–-N in young rice plants can substantially contribute to the plant-mediated N2O flux. A substantial CH4 emission through rice plants occurred at their vigorous growth stage; CH4 emissions were always lower in the presence than in the absence of inhibitor(s). Under the experimental conditions, application of DCD, especially of DCD+HQ, could significantly improve the growth of rice, and reduce the emissions of N2O and CH4 during rice growth.

Contrasting effects of ammonium and nitrate inputs on soil CO2 emission in a subtropical coniferous plantation of southern China

Increased nitrogen (N) deposition has been found controversial affecting soil CO2 emission in terrestrial ecosystems, which leads to serious debate on the efficiency of estimated C sequestration induced by N enrichment. The forms of input N might be responsible for this controversy. This study aims to explore the effects of NH4+ (reduced N) and NO3− (oxidized N) on soil CO2 flux and the underlying microbial mechanisms. An N addition experiment, two N fertilizers (NH4Cl and NaNO3) and two rates (40 and 120xa0kgxa0Nxa0ha−1xa0year−1), was carried out in a slash pine plantation of southern China. Soil-atmospheric CO2 exchange, soil microbial biomass, and community composition were measured using static chamber-gas chromatography and phospholipid fatty acid (PLFA) analyses in the active growing and nonactive growing seasons, respectively. Low level of NaNO3 addition significantly increased soil CO2 flux in the active growing season, whereas other N treatments did not change soil CO2 flux. High level of NH4Cl addition significantly reduced soil fungal biomass (fungal PLFA) and changed microbial community composition (ratio of fungal to bacterial (F/B) PLFAs). The positive relationships between the change in soil CO2 flux and the change in fungal biomass, as well as between the change in soil CO2 flux and the change in community composition, were observed in the nonactive growing season. The N forms as NO3− or NH4+ are important factors affecting C cycles in the subtropical coniferous plantation. These results suggested that the variations of soil CO2 emission and microbial biomass and community composition in the subtropical plantation depended on the seasons and the levels and forms of N addition.

Elevated atmospheric carbon dioxide concentration stimulates soil microbial activity and impacts water-extractable organic carbon in an agricultural soil

Carbon dioxide (CO2) enrichment and increased nitrogen (N) deposition can change microbial activity and dissolved organic carbon (DOC) turnover, consequently affecting carbon sequestration in soils. However, we do not have much available information on the relationship between soil DOC and microbial activity under CO2 enrichment and N addition in semi-arid agroecosystems. Using free air CO2 enrichment (FACE), soybean and winter wheat were grown in the field under ambient CO2 (350xa0μmolxa0mol−1) and elevated CO2 (550xa0μmolxa0mol−1) conditions subjected to two N fertilizer regimes (132 and 306xa0kg Nxa0ha−1xa0year−1). Rhizosphere soils and bulk soils at three depths, 0–10, 10–20 and 20–40xa0cm, were collected to determine water extractable organic matter (WEOM) characteristics with fluorescence spectroscopy and parallel factor analyses of excitation/emission matrix, as well as five extracellular enzymes activities. All significant effects were observed in the topsoil (0–10xa0cm): elevated CO2 decreased water extractable organic carbon concentration of the rhizosphere soils and bulk soils by 8.5 and 10.1xa0%, respectively. Furthermore, elevated CO2 changed the composition and structure of soil WEOM by increasing the plant- and microbial-derived components in the rhizosphere and solubilizing soil organic matter (SOM). The activities of β-1,4-glucosidase, cellobiohydrolase, phenol oxidase, and peroxidase were stimulated by elevated CO2 in the rhizosphere soils and bulk soils. Our findings suggest that the stimulation of microbial activity elicited by elevated CO2 increased the turnover of labile WEOM and the solubilization of SOM in the topsoils, which could be adverse to the accumulation and stability of soil carbon in the semi-arid agroecosystems in northern China.