Functional Plasticity and Rhizosphere Dynamics under Hydrological Seasonality in Eucalyptus Genotypes

Water seasonality strongly influences microbially mediated Soil Organic Matter (SOM) dynamics in tropical forest plantations. This study evaluated the rhizosphere response of Eucalyptus camaldulensis, E. urophylla, E. grandis, and Corymbia citriodora through exoenzyme activity (β-glucosidase and acid phosphatase) and mycorrhizal colonization. The experiment was established in 2016 in Itatinga, São Paulo State, Brazil, on a dystrophic Red-Yellow Oxisol with medium texture, according to WRB/USDA. Soil sampling was carried out in March (rainy season) and September (dry season) of 2024.

The data show that nutrient acquisition strategies diverge under water-limited conditions. During the dry season, the drought-tolerant species E. camaldulensis reached the highest acid phosphatase activity (1055.8 µg pNP g⁻¹), suggesting strong investment in the enzymatic pathway for mineralization of organic phosphorus from SOM, overcoming diffusional limitation. In contrast, E. grandis relied on ectomycorrhizal association, maintaining 40.7% colonization to cope with water stress. With the return of rainfall, β-glucosidase activity increased in all genotypes, indicating accelerated turnover of labile SOM fractions.

These results indicate that soil functional resilience is mediated by genotype-specific rhizosphere pathways. Whether through higher extracellular enzymatic potential or mycorrhizal networks, these compensatory mechanisms are essential for maintaining biogeochemical cycles during seasonal droughts in tropical ecosystems.

Nutrient cycling; Enzymes; Ectomycorrhizae; Hydrological seasonality; Climate resilience.