Seminar: Guilherme Lucio Martins

In the Amazon rainforest, soil phosphorus (P) is a limiting factor for vegetation growth. To overcome this, Amazonian plants heavily rely on organic matter cycling, mediated by soil microorganisms. However, converting forest to agriculture disrupts these critical soil-plant-microbe interactions, threatening P cycling and ecosystem stability. Our study examined the 30-year effects of converting Primary Forest into two agricultural systems: Agroforestry and Citrus monoculture. We evaluated how microbial and dissolved organic matter (DOM) composition interacted with soil physicochemical attributes and P fractions (labile, moderately labile, and non-labile). Agroforestry soils retained chemical and biological attributes similar to Forest soils, whereas Citrus soils showed higher pH and micronutrient levels but showed reduced organic matter and dissolved organic carbon content, particularly in deeper layers. Total P was greater in Citrus soils due to fertilization, while Forest and Agroforestry had proportionally larger organic P pools. Path analysis revealed the soil chemistry had the strongest effect on microbial composition and P fractions, with microbial composition further affecting DOM and P fractions. This underscores the dependence of microbial processes on organic P for nutrient cycling, especially in Forest and Agroforestry systems, while monocultures primarily rely on synthetic fertilizers to sustain productivity.