Temporal variability of soil-atmospheric CO2 and CH4 fluxes from different land uses in mid-subtropical China

Different land uses in subtropics play an important role in regulating the global environmental changes. To reduce uncertainties of greenhouse gas (GHG) emissions of agricultural soils in subtropical ecosystem, a four years campaign was started to determine the temporal GHG (CO2 and CH4) fluxes from seven sites of four land use types (1 vegetable field, 3 uplands, 2 orchards, 1 pine forest). The mean annual budgets of CO2, and CH4 were 6.5∼10.5 Mg CO2 ha−1 yr−1, and +0.47 ∼ −2.37 kg CH4 ha−1 yr−1, respectively. Pine forest had significantly lower CO2 emission and higher CH4 uptake than agriculture land uses. Tilled orchard emitted more CO2 and oxidized less CH4 than non-tilled orchard. Upland crops had higher CO2 emissions than orchards, while abrupt differences of CH4 uptake were observed between upland crops and orchards. Every year, the climate was warm and wet from April to September (the hot–humid season) and became cool and dry from October to March (the cool–dry season). Driven by seasonality of temperature and WFPS, CO2 fluxes were significantly higher in the hot–humid season than in cool–dry season. Soil temperature, WFPS, NO3−–N and NH4+–N contents interactively explained CH4 uptake which was significantly higher in cool–dry season than in hot–humid season. We conclude that soil C fluxes from different land uses are strongly under control of different climatic predictors along with soil nutrient status, which interact in conjunction with each other to supply the readily available substrates.