Abstract
Oxisol soils are widely distributed in the humid tropical and subtropical regions and are generally characterized with high contents of metal oxides. High metal oxides are believed to facilitate organic carbon (C) accumulation via mineral-organic C interactions but Oxisols often have low organic C. Yet, the causes that constrain organic C accumulation in Oxisol soil are not exactly clear. Here we report results from a microcosm experiment that evaluated how the quantity and size of crop residue fragments affect soil C retention in a typical Oxisol soil in southeast China. We found that there were significantly higher levels of dissolved organic C (DOC), microbial biomass C (MBC) and C accumulation in the heavy soil fraction in soil amended with fine-sized (<0.2 mm) compared with coarse-sized (5.0 mm) fragments. Attenuated total reflectance-Fourier transform infrared spectroscopy analysis further showed that fine-sized residues promoted stabilization of aliphatic C-H and carboxylic C=O compounds associated with mineral phases. In addition, correlation analysis revealed that the increased content of organic C in the heavy soil fraction was positively correlated with increased DOC and MBC. Together, these results suggest that enhancement of contact between organic materials and soil minerals may promote C stabilization in Oxisols.
Highlights
Emerging evidence from advanced isotopic and spectroscopic studies has recently shown that physicochemical and biological influences of the surrounding environment, rather than the recalcitrance of organic matter, play a primary role in soil organic carbon (SOC) stabilization[1, 2]
Because microbial biomass and dissolved organic C (DOC) produced during microbial decomposition of plant residues constitute a major component that interacts with soil minerals[22, 23], higher microbial activities and growth may increase DOC and microbial biomass, and facilitate soil C retention
We observed significant correlation between microbial biomass C (MBC) and SOC in the heavy soil fraction (Fig. 4a). These results suggest that over time, the MBC and MBC-derived C under the fine-sized residue treatment may constitute a significant source of stable SOC through strong physical and chemical bonding to the mineral soil matrix[20, 23]
Summary
Emerging evidence from advanced isotopic and spectroscopic studies has recently shown that physicochemical and biological influences of the surrounding environment, rather than the recalcitrance of organic matter, play a primary role in soil organic carbon (SOC) stabilization[1, 2]. Several long-term fertilization studies have shown that incorporation of organic fertilizers into the degraded Oxisol soil profile significantly enhanced the content of SOC17, 18 These results suggest that limited contact between residues and soil minerals may be an important cause that constrains organic C accumulation in Oxisols and enhancement of physical contact between crop residues and soil minerals may be a key for C sequestration. We hypothesized that (1) high residue inputs enhance C retention in the stabilized C pool due to both high plant- and microbe-derived organic C, and (2) compared to coarse-sized residue fragments, fine-sized residues increase microbial C use efficiency (that is, higher proportion for biomass production and lower for respiration) and lead to more microbially-derived DOC for organo-mineral associations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
