Organic phosphorus cycling by soil microbiota is crucial to maintaining sustainable agricultural systems in the Amazon

Most soils in the Amazon rainforest are highly weathered, acidic, and nutrient-poor. Under those conditions, most soil phosphorus (P) is bound to minerals, making it unavailable to plants and turning P into a limiting factor for plant growth. To adapt, plants in the Amazon have developed complex interactions with soil microorganisms to facilitate nutrient cycling, depending heavily on the soil organic P pool for nutrient uptake. However, converting forests into agriculture poses significant threats by disrupting the intricate interactions that maintain soil nutrient cycles and plant productivity, ultimately impacting the region's long-term stability. Our study investigated the long-term (30-year) effects of converting Primary Forest into two distinct agricultural systems: Agroforestry and Citrus monoculture. We assessed how bacterial and fungal communities interacted with soil physicochemical attributes and different P pools, such as labile, moderately labile, and non-labile P. Our preliminary results indicated that Agroforestry soils retained properties similar to those of Forest soils. In contrast, Citrus soils exhibited higher pH and micronutrient levels and reduced organic matter and dissolved organic carbon content. Total soil P was higher in Citrus soils due to fertilization, while Forest and Agroforestry had larger organic P pools, considering both soil and litter layer. Additionally, phosphatase activity and the abundance of P-cycling genes were higher in Forest and Agroforestry, suggesting greater organic P cycling and stronger reliance on microbial processes for nutrient acquisition. Bacterial and fungal composition were strongly influenced by soil micronutrient levels and the moderately labile P pool. These findings indicate that microbial processes are crucial to maintaining P cycling in Forest and Agroforestry, whereas monocultures primarily depend on synthetic fertilizers to support plant productivity. Further, our ongoing metagenomics and metabolomics analyses will provide deeper insights into functional and metabolic pathways through which organic P is cycled by soil microbiota in the Amazon region.

 

Keywords: Metagenomics; Metabolomics; Microbial Ecology; Conservative agriculture; Tropical Forest; Soil restoration.