Nitrogen deposition enhances soil organic carbon and microbial residual carbon in a tropical forest

Zhang, J. and Zhou, J. and Sayer, E.J. and Lambers, H. and Liu, Z. and Lu, X. and Li, Y. and Li, H. and Wang, F. (2023) Nitrogen deposition enhances soil organic carbon and microbial residual carbon in a tropical forest. Plant and Soil, 484. pp. 217-235. ISSN 0032-079X

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Abstract

Background: Two carbon (C) sources are of particular interest for soil organic carbon (SOC) storage under nitrogen (N) deposition: 1) glomalin-related soil protein (GRSP) and 2) microbial residual carbon (MRC) derived from microbial metabolites and residues. Both soil C sources are purported to have long residence times, but their contribution to SOC may be modified by changing soil N status. Methods: We assessed how N deposition influences GRSP and MRC as sources of SOC using soils from a long-term (11 years) N-addition site in a tropical forest in south China. We assessed differences in MRC and GRSP, microbial biomarkers, soil physico-chemical properties, and particle-size fractions between N-fertilized soils and controls. Results: Total GRSP, MRC, and SOC concentrations were higher under N-addition, but soil microbial biomass and community composition were largely unaffected, indicating that higher GRSP and MRC concentrations resulted from long-term accumulation and reduced microbial degradation. However, the relative contributions of GRSP or MRC to SOC were unchanged or lower than the controls due to a greater contribution of other C sources to SOC which were largely unstabilized by association with soil minerals. Conclusion: Tropical forests have great potential for SOC sequestration in response to N deposition which may help mitigate climate change. However, most of the additional SOC in N-fertilized soils was not associated with soil minerals, and thus prone to decomposition.