Variations and controlling factors of carbon dioxide and methane fluxes in a meadow-rice ecosystem in a semi-arid region

Abstract

Although previous studies have illustrated the variations in carbon dioxide (CO2) and methane (CH4) fluxes for different types of wetlands, there have been few reports on those of meadow-rice mixed ecosystems in semi-arid regions. In this study, eddy covariance (EC) technique was utilized to measure CO2 and CH4 fluxes for a meadow-rice mixed ecosystem during the growing season in 2020 in the Horqin Sandy Land, North China. The results indicated obvious diurnal and seasonal variations in gross primary productivity (GPP), ecosystem respiration (Reco), net CO2 exchange (NEE), and CH4 flux, with high levels during the vigorous growing stage and low levels during the early and late growing stages. The mean daily GPP, Reco, NEE, and CH4 were 11.33 g CO2 m−2 d−1, 6.37 g CO2 m−2 d−1, −4.96 g CO2 m−2 d−1, and 81.97 mg CH4 m−2 d−1, respectively. The accumulated values of GPP, Reco, NEE, and CH4 during the growing season were 1,756.54 g CO2 m−2 (478.62 g C m−2), 987.30 g CO2 m−2 (269.02 g C m−2), −769.24 g CO2 m−2 (−209.60 g C m−2), and 12.7 g CH4 m−2 (9.55 g C m−2), respectively, showing that the meadow-rice mixed ecosystem acted as CO2 sink and CH4 source. Low intensity CH4 emissions were maintained during the dry period and were controlled by soil moisture (SM). The seasonal dynamics of GPP, Reco, and CH4 throughout the growing season were mainly controlled by soil temperature (Ts) and air temperature (Ta).