Nitrate as an alternative electron acceptor destabilizes the mineral associated organic carbon in moisturized deep soil depths

Wei Song; Chunsheng Hu; Yu Luo; Tim J Clough; Nicole Wrage-Mönnig; Tida Ge; Jiafa Luo; Shungui Zhou; Shuping Qin

doi:10.3389/fmicb.2023.1120466

Nitrate as an alternative electron acceptor destabilizes the mineral associated organic carbon in moisturized deep soil depths

Front Microbiol. 2023 Feb 8:14:1120466. doi: 10.3389/fmicb.2023.1120466. eCollection 2023.

Authors

Wei Song¹, Chunsheng Hu², Yu Luo³, Tim J Clough⁴, Nicole Wrage-Mönnig⁵, Tida Ge⁶, Jiafa Luo⁷, Shungui Zhou¹, Shuping Qin²

Affiliations

¹ Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, Fujian, China.
² Hebei Provincial Key Laboratory of Soil Ecology, Center for Agricultural Resources Research, Institute of Genetic and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang, Hebei, China.
³ Zhejiang Provincial Key Laboratory of Agricultural Resources and Environment, Institute of Soil and Water Resources and Environmental Science, Zhejiang University, Hangzhou, China.
⁴ Faculty of Agriculture and Life Sciences, Lincoln University, Lincoln, New Zealand.
⁵ Faculty of Agricultural and Environmental Sciences, Grassland and Fodder Sciences, University of Rostock, Rostock, Germany.
⁶ State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-Products, Key Laboratory of Biotechnology in Plant Protection of Ministry of Agriculture and Zhejiang Province, Institute of Plant Virology, Ningbo University, Ningbo, China.
⁷ AgResearch Ltd., Hamilton, New Zealand.

Abstract

Numerous studies have investigated the effects of nitrogen (N) addition on soil organic carbon (SOC) decomposition. However, most studies have focused on the shallow top soils <0.2 m (surface soil), with a few studies also examining the deeper soil depths of 0.5-1.0 m (subsoil). Studies investigating the effects of N addition on SOC decomposition in soil >1.0 m deep (deep soil) are rare. Here, we investigated the effects and the underlying mechanisms of nitrate addition on SOC stability in soil depths deeper than 1.0 m. The results showed that nitrate addition promoted deep soil respiration if the stoichiometric mole ratio of nitrate to O₂ exceeded the threshold of 6:1, at which nitrate can be used as an alternative acceptor to O₂ for microbial respiration. In addition, the mole ratio of the produced CO₂ to N₂O was 2.57:1, which is close to the theoretical ratio of 2:1 expected when nitrate is used as an electron acceptor for microbial respiration. These results demonstrated that nitrate, as an alternative acceptor to O₂, promoted microbial carbon decomposition in deep soil. Furthermore, our results showed that nitrate addition increased the abundance of SOC decomposers and the expressions of their functional genes, and concurrently decreased MAOC, and the ratio of MAOC/SOC decreased from 20% before incubation to 4% at the end of incubation. Thus, nitrate can destabilize the MAOC in deep soils by stimulating microbial utilization of MAOC. Our results imply a new mechanism on how above-ground anthropogenic N inputs affect MAOC stability in deep soil. Mitigation of nitrate leaching is expected to benefit the conservation of MAOC in deep soil depths.

Keywords: MAOC; deep soil; global warming; greenhouse gas emission; nitrate leaching.

Grants and funding

This work was supported by the National Key R&D Program of China (2021YFD1500400), the National Natural Science Foundation of Hebei Province (D2022503014), and the National Natural Science Foundation of China (No. 41771331).