[CH₄ Uptake in Different Saline-alkaline Soils in Hetao Irrigation District, Inner Mongolia]

Soil salinization poses a great threat to sustainable land use and the limitation of greenhouse gas emissions. In this study, three saline alkali soils, saline soil[electrical conductivity (EC) 4.80 dS·m^-1], high saline-alkaline soil (EC 2.60 dS·m^-1), and low saline-alkaline soil (EC 0.74 dS·m^-1) in the Hetao Irrigation District of Inner Mongolia were selected as research plots. Field experiments were conducted to study the uptake of methane (CH₄) in the crop-growing season (April-October) for three years (2014-2016) using the static box method. There were significant differences in the soil CH₄ uptake among the soil types in 2014 (F=18.0, P<0.001), 2015 (F=23.6, P<0.001), and 2016 (F=28.4, P<0.001). The uptake of CH₄ by the soil decreases with increasing soil salinity. The accumulated CH₄ uptake was 150.0 mg·m^-2, 119.6 mg·m^-2, and 99.9 mg·m^-2 in the low saline-alkaline, high saline-alkaline, and saline soil in 2014, respectively. The cumulative uptake of CH₄ was 27%, 28%, and 19% lower in the high saline-alkaline soil and 35%, 35%, and 53% lower in the saline soil than in the low saline-alkaline soil in 2014, 2015, and 2016, respectively. Redundancy analysis shows that the projection of the CH₄ uptake flux and EC of saline-alkaline soil are in the positive direction, and in the opposite direction to the first principal component axis. The higher the soil EC, the lower the CH₄ uptake flux. Soil EC was found to be the key factor controlling the uptakes of CH₄, with a correlation coefficient (r) of -0.8809 (P<0.01, n=9).