Carbon isotope fractionation (CIF) of agro ecosystem respiration has a fundamental value for probing the microcosmic mechanism of ecological process in agriculture carbon cycle. The North China Plain (NCP) is the typical high-yield area of a winter-wheat (Carbon 3)/summer-maize (Carbon 4) double cropping system. The CIF of respiration process in this special system is still not well understood. This study was conducted in a winter-wheat (Carbon 3)/summer-maize (Carbon 4) double cropping rotation system in 2015 in the NCP. Ecosystem respiration (FR) and its carbon isotope signature (δFR) were measured in situ by using an eddy covariance system and a CO2 isotope analyzer system, respectively. Soil respiration (FRs), soil heterotrophic respiration (FR,sh) and their carbon isotope signatures (δSR) were measured by using static chamber-gas chromatograph technique and mass spectrometry technique, respectively. The objectives of this study were to clarify the CIF during respiration process at soil-atmosphere interface and find the mechanism of the effects of abiotic factors on the CIF of respiration process in a winter-wheat/summer-maize double cropping system in the NCP.
Results/Conclusions
We found the evolution of net ecosystem carbon exchange (NEE) and ecosystem respiration (FR) clearly depicts the double cropping system (a typical double-peak curve), which is characteristic for the NCP. The values were fairly small during the autumn and winter seasons; while these became fairly high during the spring and summer seasons, which related to crop development. The FR, FRs, FR,sh, FR,ag (above-ground respiration) and FR,bg (below-ground respiration) showed the same trends with the average values of 642.5, 352.4, 164.3, 290.1 and 188.1 mg CO2 m-2 hr-1 in wheat season and 1112.9, 519.3, 312.5, 593.5 and 206.8 mg CO2 m-2 hr-1 in maize season, respectively. Meanwhile, the δR, δRs, δR,sh, δR,ag and δR,bg were more depleted during the vigorous growth stages in both wheat and maize seasons. And the average values of those were -24.9, -21.7, -19.8, -26.5 and -23.0‰ in wheat season and -22.8, -20.5, -18.8, -24.1 and -22.9‰ in maize season, respectively. Furthermore, our results indicated that the signatures of CIF in respiration processes were fairly sensitive to changes in soil and air temperatures (p˂0.05). In conclusion, we quantified the CIF effects during respiration processes in a winter-wheat (Carbon 3)/summer-maize (Carbon 4) double cropping system in the NCP.