CH₄ flux characteristics and influencing factors in six land use patterns in the Loess Plateau

Change in land use can influence soil micro-environment along with microbial, physiological and biochemical processes, significantly affecting the generation and emission of greenhouse gases. At present, researches on greenhouse gas flux from land use transformation have mainly focused on carbon dioxide (CO₂), largely neglecting methane (CH₄) generation and emission. This study determined the characteristics of soil CH₄ fluxes and the influencing factors, also highlighting the critical factors of different land use patterns (cultivated land, natural grassland, shrub land, arbor and shrub land, arbor land and orchard). The study laid the basis for predicting the contribution of land-use-driven transformation to greenhouse effects in the Loess Plateau region. The study was conducted in Malian Forest Farm of Yongshou County, Shaanxi Province. In the study, soil CH₄ fluxes in different land use types were measured during the period from April 2015 to March 2016 using static chamber chromatograph techniques. The related environmental factors were recorded, including soil temperature, soil moisture, surface temperature and soil total nitrogen content. The results indicated that soils were CH₄ sink under different land use types. There were significant differences (P < 0.05) in CH₄ uptake fluxes in different land use types. Soil CH₄ fluxes in six land use types had similar seasonal variations, higher in summer and autumn than in winter and spring. Average soil CH₄ uptake was in the order of arbor and shrub land (51.24 μg·m^-2·h^-1) > arbor land (44.80 μg·m^-2·h^-1) > shrub land (31.52 μg·m^-2·h^-1) > natural grassland (25.89 μg·m^-2·h^-1) > orchard (18.97 μg·m^-2·h^-1) > cultivated land (14.89 μg·m^-2·h^-1). Soil CH₄ uptake fluxes in different land use types were positively correlated with soil temperature, surface temperature and total nitrogen, and negatively correlated with soil moisture. Soil temperature at the 0-20 cm soil layer was the main layer of production of soil CH₄ fluxes in six land use types. The uptake CH₄ under natural soil conditions was significantly higher than that in agricultural soils. The transformation of cultivated land to forest land increased CH₄ uptake, enhancing the mitigation of greenhouse effect of soil.