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.
Soil physical properties and maize root growth under different tillage systems in the North China Plain