Mineralization of Goethite-Adsorbed and -Encapsulated Organic Carbon and Its Priming Effect in Paddy Soil
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X144

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The National Natural Science Foundation of China (General Program, Key Program, Major Research Plan)

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    Abstract:

    [Objective] The paddy soil in South China rich in iron oxides has soil organic carbon (OC) stored for a long time in association with iron oxides. As the iron oxide and organic carbon in the soil exist mainly in adsorbed-, bonded, and encapsulated forms, the carbon-goethite association vary in stability with the form. Although a large volume of studies have analyzed how OC and iron oxides associate in the soil and what form they exist in. However, so far little is known about mechanism of the association, relative to type, between iron oxides and OC affecting mineralization of OC and its priming effects (PE) in paddy soil.[Method] Glucose was used as the typical low molecular weight exogenous C, and prepared into goethite-adsorbed glucose (Goe-G) and goethite-encapsulated glucose (Goe*G), which were then incubated in the experiment to explore characteristics of the mineralization of the two iron oxides-glucose associations and their PE in paddy soil.[Result] Results show that compared with the pots amended with glucose alone, the pots amended with the two types of carbon-goethite association, separately, had CO2 and 13CO2 emission increased by 0.39-0.53 times and 0.87-1.07 times, respectively, and CH4 and 13CH4 emission decreased by 0.44-0.59 fold and 0.25-0.44 fold, respectively. Relative to amendment of goethite-adsorbed glucose, amendment of goethite-encapsulated glucose significantly inhibited CH4 release. What is more, amendment of carbon-goethite association, regardless of type, promoted the mineralization of SOC into CO2 but inhibited the release of native SOC-derived CH4. The inhibitory effect of goethite-encapsulated glucose on the release of native SOC-derived CH4 was significantly greater than that of goethite adsorbed glucose. The fast pool of goethite-encapsulated glucose was higher than that of goethite adsorbed glucose, and its half-life (T1/2) was 10.85 times longer than that of goethite adsorbed glucose, and the turnover rate of the fast pool (k1) and slow pool (k2) was 10.74 and 19 times smaller than that of the goethite adsorbed glucose, respectively. Secondly, the goethite encapsulated glucose-induced a weak positive PE for CO2 emission (6.44 mg·kg-1), but a negative PE for CH4 emission (-15.49 mg·kg-1). The findings suggest that the amendment of goethite-encapsulated glucose inhibits mineralization of native SOC(-9.05 mg·kg-1) and enhances the potential of C assimilation in the paddy soil. Though the addition of either carbon-goethite association has the effect inhibiting mineralization of native SOC, the amendment of goethite-encapsulated OC is more beneficial than that of goethite-adsorbed OC to soil C stabilization and sequestration.[Conclusion] The findings in the experiment suggest that iron-oxides-bonded low molecular weight OC is higher in biological stability than soluble OC, but relatively low in mineralization rate, thus inhibiting mineralization of native SOC and inducing negative priming effect. Therefore, amendment of OC bonded with iron oxides is beneficial to long-term C sequestration effect in paddy soils.

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JIANG Jiabin, ZHU Zhenke, LIN Sen, LI Yuhong, LI Kelin, WANG Xiaoli, GE Tida, WU Jinshui. Mineralization of Goethite-Adsorbed and -Encapsulated Organic Carbon and Its Priming Effect in Paddy Soil[J]. Acta Pedologica Sinica,2021,58(6):1530-1539.

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History
  • Received:May 05,2020
  • Revised:June 26,2020
  • Adopted:August 20,2020
  • Online: December 31,2020
  • Published: November 11,2021