Carbon Balance Characteristic And Its Controlling Factors In A Winter Wheat-summer Maize Rotation Cropland Over The North China Plain

The North China Plain is an important region for food production in China,obataining its carbon cycle and controlling factors therefore contributes to evaluate thecarbon emission of this region. We conducted field experiment to measure componentsof carbon balance, and the corresponding controlling mechanisms were theninvestigated. The measurements were used to calibrate and validate the carbon cyclemodel DNDC. The calibrated DNDC was then used to simulate the variations of carbonflux for this typical cropland from1984to2007, the sensitivities of carbon flux andcarbon balance to field management practices were also investigated.Soil respiration is the second largest carbon flux between the terrestrial ecosystemand the atmosphere. We conducted soil respiration measurements to obtain thecharacteristics of soil respiration and its controlling mechanisms in the North ChinaPlain. The “root exclusion method” was applied to partition soil respiration into itsheterotrophic and autotrophic components. In diurnal scale, heterotrophic respirationcorrelates linearly with relative humidity, while autotrophic respiration correlates wellwith photosynthesis rate. In seasonal scale, heterotrophic respiration is mainlycontrolled by soil temperature and soil moisture, while autotrophic respiration is mainlycontrolled by soil temperature and photosynthesis rate. The contribution ratio ofautotrophic respiration to total soil respiration were36%and29%for the wheat andmaize season, respectively. In diurnal scale, a hysteresis exists between soil respirationand soil temperature. A model of simulating subsurface gas-phase CO2transport wasdeveloped to investigate this hysteresis phenomenon. The results showed that soilmoisture and photosynthesis regulate the hysteresis phenomenon.Integrating measurements of soil respiration and the eddy covariance allowsinvestigating the seasonal variations of all carbon components (Gross PrimaryProductivity (GPP), Ecosystem Respiration (ER), as well as the three component of ER,i.e., soil heterotrophic respiration, soil autrotrophic respiration and plant above groundautotrophic respiration). Furthermore, Net Primary Productivity (NPP), Net EcosystemProductivity (NEP), and Net Biome Productivity (NBP) were estimated based on thesemeasurements. For the2010~2011whole seasons of the wheat and the maize, NPPwere769.0and561.3gC m-2, respectively. NEP were417.6and269.1gC m-2, respectively. NBP was70.9and3.9gC m-2, respectively. NBP was12.3gC m-2for thewhole2010~2011rotation season of wheat and maize, the typical cropland wastherefore a tiny carbon sink for the atmosphere.These measurements were then used to calibrate and validate the carbon cyclemodel DNDC, and results showed that DNDC is capable of simulating NEE, GPP, NPPand food production. The DNDC model was then used to simulate the variations ofcarbon flux of this typical cropland from1984to2007. DNDC was finally used toinvestigate the sensitivity of carbon flux and carbon balance to cropland managementpractices, and results showed that carbon flux are significantly influenced by irrigationand fertilization, while tillage depth has little effect on carbon flux. Irrigation andfertilization have little effect on NBP, while no-tillage helps increase NBP, i.e., increasethe capacity of carbon sink of the cropland.