Carbon exchange of a rainfed spring maize cropland under plastic film mulching with straw returning on the Loess Plateau, China

•The seasonal variations of carbon fluxes are mainly controlled by GLAI.•The diurnal and seasonal variations of Re are driven by GPP.•The seasonal variations of α, Pmax, and R10 are mainly controlled by GLAI.•The cropland acts as a carbon sink with mean annual sequestration of 59 g C m− 2.

Increasing attention has been paid to the potential of croplands to mitigate rising atmospheric CO2 concentrations by adopting appropriate cultivation practices. Plastic film mulching with straw returning to promote crop yields is widely used in rainfed agriculture; however, information about the effect of this practice on carbon exchange is limited. Eddy covariance measurements were used to investigate carbon fluxes in a rainfed spring maize cropland under plastic film mulching with straw returning on the Chinese Loess Plateau in 2013 and 2014. Carbon fluxes showed a clear seasonal variation, with the green leaf area index (GLAI) being the dominant control factor. The diurnal and seasonal ecosystem respiration (Re) values were driven by gross primary productivity (GPP), and the daily Re per unit daily GPP increased by 0.32 g C m− 2 d− 1. The ecosystem apparent quantum yield (α), ecosystem maximum photosynthetic capacity (Pmax), and ecosystem respiration rate at 10 °C (R10) also showed clear seasonal variations, and the mean monthly α, Pmax, and R10 per unit mean monthly GLAI increased by 1.44 × 10− 2 μmol CO2 μmol PAR− 1, 1.12 mg CO2 m− 2 s− 1, and 2.08 × 10− 2 mg CO2 m− 2 s− 1 respectively. The temperature sensitivity of ecosystem respiration was insensitive to GLAI, and ranged from 1.58 to 2.85, with the maximum value appearing in the non-growth seasons. Annual GPP values were 1547 and 1370 g C m− 2 in 2013 and 2014, respectively, approximately 60% of which was lost through Re, which resulted in annual net CO2 uptakes of 618 and 540 g C m− 2 in 2013 and 2014 respectively. Compared to the non-mulching spring maize field with straw returning, the spring maize field under plastic film mulching with straw returning was a stronger carbon sink (76 and 41 g C m− 2 in 2013 and 2014, respectively). Plastic film mulching with straw returning is recommended as an effective approach to sequester carbon in rainfed spring maize cropland on the Loess Plateau and to mitigate greenhouse effects.