Abstract
Abstract. Carbon sequestration in agroecosystems has great potential to mitigate global greenhouse gas emissions. To assess the decadal trend of CO2 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 CO2 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 −364, 1174, and 810 gC m−2 for wheat and −136, 1008, and 872 gC m−2 for maize. The multiple regression revealed that air temperature and groundwater depth showed pronounced correlations with the CO2 fluxes for wheat. However, in the maize season, incoming shortwave radiation and groundwater depth showed pronounced correlations with CO2 fluxes. For the full 2010–2011 agricultural cycle, the CO2 fluxes for wheat and maize were as follows: for NEE they were −438 and −239 gC m−2, for GPP 1078 and 780 gC m−2, for ER 640 and 541 gC m−2, for soil heterotrophic respiration 377 and 292 gC m−2, for below-ground autotrophic respiration 136 and 115 gC m−2, and for above-ground autotrophic respiration 128 and 133 gC m−2. The net biome productivity was 59 gC m−2 for wheat and 5 gC m−2 for maize, indicating that wheat was a weak CO2 sink and maize was close to CO2 neutral to the atmosphere for this agricultural cycle. However, when considering the total CO2 loss in the fallow period, the net biome productivity was −40 gC m−2 yr−1 for the full 2010–2011 cycle, implying that the cropland was a weak CO2 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 CO2 sequestration potential of croplands.
Highlights
The widely used eddy covariance technique (Aubinet et al, 2000; Baldocchi et al, 2001; Falge et al, 2002a, b) has enabled us to better understand the terrestrial CO2 exchange with the atmosphere, and has thereby fostered our understanding of the mechanisms through which terrestrial ecosystems contribute to mitigating ongoing climate change (Falkowski et al, 2000; Gray et al, 2014; Poulter et al, 2014; Forkel et al, 2016)
The seasonal maximum and minimum Ta occurred in July and January, respectively, and the variations in vapor pressure deficit (VPD) followed the Ta well
This study investigated the decadal variations in the net ecosystem exchange (NEE), gross primary productivity (GPP) and ecosystem respiration (ER) for an irrigated wheat–maize rotation cropland over the North China Plain, and the results exhibited a decreasing trend of the CO2 sink capacity during the past decade
Summary
The widely used eddy covariance technique (Aubinet et al, 2000; Baldocchi et al, 2001; Falge et al, 2002a, b) has enabled us to better understand the terrestrial CO2 exchange with the atmosphere, and has thereby fostered our understanding of the mechanisms through which terrestrial ecosystems contribute to mitigating ongoing climate change (Falkowski et al, 2000; Gray et al, 2014; Poulter et al, 2014; Forkel et al, 2016). Agroecosystems play an important role in regulating the global carbon balance (Lal, 2001; Bondeau et al, 2007; Özdogan, 2011; Taylor et al, 2013; Gray et al, 2014) and are believed to have great potential to mitigate global carbon emissions through cropland management Some studies proposed using agroecosystems as “natural climate solutions” to mitigate global carbon emissions (e.g., Griscom et al, 2017; Fargione et al, 2018). Field management practices (e.g., irrigation, fertilization and residue removal, etc.) impact the cropland CO2 fluxes (Baker and Griffis, 2005; Béziat et al, 2009; Ceschia et al, 2010; Eugster et al, 2010; Drewniak et al, 2015; de la Motte et al, 2016; Hunt et al, 2016; Vick et al, 2016), but their relative importance in determining the cropland CO2 budget remain unclear because of limited field observations (Kutsch et al, 2010), motivating comprehensive CO2 budget assessments across different cropland management styles
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