Abstract: Cropland is an important type of terrestrial ecosystem. Maize is the grain crop with the largest planting area and production in China. In the context of climate change, accurately evaluating the carbon source and sink characteristics of summer maize cropland is of great significance to improving cropland carbon sequestration capacity. In this study, we collected the meteorological data during 1991-2022 from Zhengzhou National Basic Meteorological Station and the data of CO₂ flux, meteorological factors, and biomass and yield of summer maize during 2008-2022 from Zhengzhou Agrometeorology Experiment Station. Based on these data, we analyzed the change characteristics of climate variables and CO₂ flux and the carbon source and sink characteristics of summer maize cropland. The results showed that there were obvious daily and seasonal change characteristics of CO₂ flux of summer maize cropland ecosystem. It was a carbon sink from July to September but a carbon source in June. The CO₂ flux of summer maize cropland was different under different climate year types. The annual average of gross primary productivity (GPP) and ecosystem respiration (R_eco) of summer maize cropland was 1197.5±129.9 g C·m^-2·a^-1 and 711.2±129.9 g C·m^-2·a^-1, respectively. Without including grains after harvest, summer maize cropland ecosystem was a carbon sink, with multi-year mean value of net ecosystem exchange (NEE) being -342.8±52.3 g C·m^-2·a^-1. After the grains were harvested and removed from the cropland, summer maize cropland exhibited a weak carbon sink, with a net biome productivity (NBP) of -41.3 g C·m^-2·a^-1 (12.0% of NEE) based on calculated theoretical yield. Based on actual yield, summer maize cropland exhibited a strong carbon sink, with a NBP of -105.9 g C·m^-2·a^-1 (30.9% of NEE). The climate in this area showed a warm-dry tendency. Temperature and precipitation did not affect CO₂ flux of summer maize cropland ecosystem. In contrast, sunshine duration had a significant impact on GPP of summer maize cropland ecosystem (P<0.05), and indirectly affected net ecosystem productivity (NEP) and R_eco through GPP (P<0.05). In the summer maize growing season, GPP and NPP increased by 19.4 g C·m^-2·a^-1 and 6.6 g C·m^-2·a^-1 respectively when sunshine duration increased by 15.6 h·a^-1. Our results indicate that summer maize cropland ecosystem has a large carbon sequestration potential.

Key words: climate change, summer maize cropland ecosystem, carbon source/sink, net ecosystem carbon exchange, carbon peak and carbon neutrality