Long-term residue returning increased subsoil carbon quality in a rice-wheat cropping system

Yinan Xu; Yalin Yu; Jing Sheng; Yuekai Wang; Haishui Yang; Feng-Min Li; Shiping Liu; Zheng-Rong Kan

doi:10.1016/j.jenvman.2024.121088

Long-term residue returning increased subsoil carbon quality in a rice-wheat cropping system

J Environ Manage. 2024 May 11:360:121088. doi: 10.1016/j.jenvman.2024.121088. Online ahead of print.

Authors

Yinan Xu¹, Yalin Yu², Jing Sheng¹, Yuekai Wang², Haishui Yang², Feng-Min Li², Shiping Liu³, Zheng-Rong Kan⁴

Affiliations

¹ Institute of Agricultural Resources and Environment, Jiangsu Academy of Agricultural Sciences, Nanjing, 210014, China.
² College of Agriculture, Nanjing Agricultural University, Nanjing, 210095, China.
³ Yangzhou University, Yangzhou, 225000, China. Electronic address: spliu@yzu.edu.cn.
⁴ College of Agriculture, Nanjing Agricultural University, Nanjing, 210095, China. Electronic address: kzr@njau.edu.cn.

PMID: 38735070
DOI: 10.1016/j.jenvman.2024.121088

Abstract

Residue returning (RR) was widely implemented to increase soil organic carbon (SOC) in farmland. Extensive studies concentrated on the effects of RR on SOC quantity instead of SOC fractions at aggregate scales. This study investigated the effects of 20-year RR on the distribution of labile (e.g., dissolved, microbial biomass, and permanganate oxidizable organic) and stable (e.g., microbial necromass) carbon fractions at aggregate scales, as well as their contribution to SOC accumulation and mineralization. The findings indicated a synchronized variation in the carbon content of bacterial and fungal necromass. Residue retention (RR) notably elevated the concentration of bacterial and fungal necromass carbon, while it did not amplify the microbial necromass carbon (MNC) contribution to SOC when compared to residue removal (R0) in the topsoil (0-5 cm). In the subsoil (5-15 cm), RR increased the MNC contribution to SOC concentration by 21.2%-33.4% and mitigated SOC mineralization by 12.6% in micro-aggregates (P < 0.05). Besides, RR increased soil β-glucosidase and peroxidase activities but decreased soil phenol oxidase activity in micro-aggregates (P < 0.05). These indicated that RR might accelerate cellulose degradation and conversion to stable microbial necromass C, and thus RR improved SOC stability because SOC occluded in micro-aggregates were more stable. Interestingly, SOC concentration was mainly regulated by MNC, while SOC mineralization was by dissolved organic carbon under RR, both of which were affected by soil carbon, nitrogen, and phosphorus associated nutrients and enzyme activities. The findings of this study emphasize that the paths of RR-induced SOC accumulation and mineralization were different, and depended on stable and labile C, respectively. Overall, long-term RR increased topsoil carbon quantity and subsoil carbon quality.

Keywords: Carbon fractions; Carbon mineralization; Microbial necromass carbon; Residue returning; Soil depth.