Mineralization And Potential Carbon Sequestration Effect Of Rice Straw-derived Biochar In Flooded Paddy Soil

To tackle with the increasing global warming, it is urgent to take research on the technique of carbon capture and storage (CCS). Biochar can persist in the natural environment for centuries to millennia due to its chemical and biological recalcitrance. Therefore, it is widely recognized that biochar application in soil ecosystem is a promising method for carbon sequestration. Biochar stability and carbon sequestration effect in soil ecosystem, which determines the capability of biochar application as an effective CCS technique, is not only influenced by biochar physicochemical characteristics but also soil properties and environmental conditions. In addition, in order to evaluate environmental effect of biochar application from a comprehensive perspective, biochar carbon sequestration effect in soil ecosystem is needed to be predicted and estimated. In this thesis, rice straw-derived (RS) biochar carbon mineralization in different types of paddy soils was investigated using stable carbon isotope labeling and analysis. Moreover, through the simulation of carbon mineralization process using double exponential model, mean residence time (MRT) and carbon sequestration effect of RS biochar in paddy soil was estimated. The obtained results could provide powerful theoretical evidence for evaluating the carbon sequestration effect of straw biochar application to paddy soil. The main results are summarized as follow:(1) RS biochar carbon mineralization was investigated in five selected paddy soils, which are different from each other in latitude. Results showed that biochar carbon cumulative mineralization rates ranged from 0.17%-0.28% in different types of paddy soils during 390 days of incubation. It may suggest that this herbaceous plants derived biochar at 500℃ is similarly recalcitrant with woody plant biochar. In addition, biochar carbon cumulative mineralization rates after 150 days were significantly positively correlated with total organic carbon (TOC) in different paddy soils. This suggested that microbial co-metabolism function increased with the increasing TOC and thus increased biochar carbon cumulative mineralization rates at the later incubation stage.(2) MRT of RS Biochar and its carbon sequestration effect in different paddy soils were analyzed through the simulation of carbon mineralization process using double exponential model. Results showed that MRT of biochar labile carbon components ranged from 18-37 days, while stable carbon components ranged from 617-2829 years and were significantly correlated with soil TOC. It suggested that from the perspective of long-term carbon sequestration, biochar application is more suitable for paddy soils with low TOC.(3) FTIR and XPS analyses showed that oxidation occurred for RSD biochar in paddy soils by changing C components from C-C/C-H/C=C to C in oxidation states (C-O、C=O and COO). After being incubated with GD soil, the relative content of C-C/C-H/C=C in RSD biochar declined more compared with other soils. It suggested that RSD biochar incubated with GD soil showed more oxidation than other soils, which could be due to the adsorption of C-O-C functional groups derived from organic matter in GD soil.