Decadal variation in CO 2 fluxes and its budget in a wheat and maize rotation cropland over the North China Plain

Zhang, Quan; Lei, Huimin; Yang, Dawen; Xiong, Lihua; Liu, Pan; Fang, Beijing

Carbon sequestration in agroecosystems has great potential to mitigate global greenhouse gas emissions. To assess the decadal trend of inline-formulaCO2 fluxes of an irrigated wheat–maize rotation cropland over the North China Plain, the net ecosystem exchange (NEE) with the atmosphere was measured by using an eddy covariance system from 2005 to 2016. To evaluate the detailed inline-formulaCO2 budget components of this representative cropland, a comprehensive experiment was conducted in the full 2010–2011 wheat–maize rotation cycle by combining the eddy covariance NEE measurements, plant carbon storage samples, and a soil respiration experiment that differentiated between heterotrophic and below-ground autotrophic respirations. Over the past decade (from 2005 to 2016), the cropland exhibited a statistically nonsignificant decreasing carbon sequestration capacity; the average of total NEE, gross primary productivity (GPP), and ecosystem respiration (ER), respectively, were inline-formula−364, 1174, and 810 gC minline-formula−2 for wheat and inline-formula−136, 1008, and 872 gC minline-formula−2 for maize. The multiple regression revealed that air temperature and groundwater depth showed pronounced correlations with the inline-formulaCO2 fluxes for wheat. However, in the maize season, incoming shortwave radiation and groundwater depth showed pronounced correlations with inline-formulaCO2 fluxes. For the full 2010–2011 agricultural cycle, the inline-formulaCO2 fluxes for wheat and maize were as follows: for NEE they were inline-formula−438 and inline-formula−239 gC minline-formula−2, for GPP 1078 and 780 gC minline-formula−2, for ER 640 and 541 gC minline-formula−2, for soil heterotrophic respiration 377 and 292 gC minline-formula−2, for below-ground autotrophic respiration 136 and 115 gC minline-formula−2, and for above-ground autotrophic respiration 128 and 133 gC minline-formula−2. The net biome productivity was 59 gC minline-formula−2 for wheat and 5 gC minline-formula−2 for maize, indicating that wheat was a weak inline-formulaCO2 sink and maize was close to inline-formulaCO2 neutral to the atmosphere for this agricultural cycle. However, when considering the total inline-formulaCO2 loss in the fallow period, the net biome productivity was inline-formula−40 gC minline-formula−2 yrinline-formula−1 for the full 2010–2011 cycle, implying that the cropland was a weak inline-formulaCO2 source. The investigations of this study showed that taking cropland as a climate change mitigation tool is challenging and that further studies are required for the inline-formulaCO2 sequestration potential of croplands.

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Zhang, Quan / Lei, Huimin / Yang, Dawen / et al: Decadal variation in CO2 fluxes and its budget in a wheat and maize rotation cropland over the North China Plain. 2020. Copernicus Publications.

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