Microbial necromass, carbon and agriculture: combining living and dead microbes to reveal carbon dynamics under agroforestry in the Amazon

• Ano de defesa: 2024
• Autor(a) principal: Rocha, Alberto Vinicius Sousa
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Agroforestry systems; carbono orgânico do solo; comunidades microbianas do solo; cultivo de dendê; microbial necromass; necromassa microbiana; oil palm plantation; Sistemas agroflorestais; soil microbial communities; soil organic carbon
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/11/11140/tde-10092024-152039/

Soil microbes are reported to mediate and, more recently, also contribute to soil organic carbon (SOC) persistence through microbial necromass. However, factors such as climate, land use, and microbial attributes (activity and diversity) strongly influence microbial life and death cycles and therefore the accumulation of microbialderived C, mainly in tropical regions. Thereby, we used replicated oil palm (Elaeis guineenses) plots in an oil palm-cropland agroforestry system (AFS) and in oil palm monoculture (hereafter conventional agriculture, CA) in the Brazilian Amazon to investigate the impacts of land use (agricultural management), soil depth, and seasonality on extracellular enzymatic activity and the microbial necromass C pool. In addition, we also assessed C contents in the physical fractions of soil organic matter (SOM) (C-POM and C-MAOM) and on the assembly of soil bacterial and fungal communities associated with each land use. Collectively, our results demonstrated that the adoption of AFS, based on land cover diversification, significantly increases SOC, C-POM, C-MAOM and the activity of enzymes related to the C (β-glucosidase, in general), S (arylsulfatase) and partially P (acid phosphatase) cycles compared to CA along the vertical soil profile. It also promotes the content of fungal and total necromass, but not necessarily bacterial necromass, with the volume of necromass being dominated by fungal necromass. Interestingly, the microbial necromass:SOC ratio was lower in AFS and/or equal to CA and sometimes increased with soil depth (maximum accounted was ~28%). Moreover, the composition, richness and diversity of microbial communities (bacteria and fungi) were assembled according to land use and promoted important effects on soil functioning, including C fluxes. Lastly, C-POM, C-MAOM and the activity of β-glucosidase and arylsulfatase, as well as fungal diversity indices, exchangeable Ca2+ and clay content were the most important attributes to predict necromass. Our findings showed a critical role of land cover in soil C dynamics and underline the real effect of agroforestry on promoting total C and functionally distinct forms of C in organic matter, as well as specific microbial traits. In addition, they provide the first insights into the pathways of necromass C accumulation in agricultural systems in the Brazilian Amazon.