Fine Root Density Dynamics and Carbon Stock of <i>Eucalyptus</i> spp.: Interplay of Age, Genotype, and Edaphoclimatic Conditions

Roots play a fundamental role in forest ecosystems, but obtaining samples from deep layers remains a challenging process due to the methodological and financial efforts required. In our quest to understand the dynamics of <i>Eucalyptus</i> roots, we raise three fundamental questions. First, we inquire about the average extent of the roots of two contrasting <i>Eucalyptus</i> genotypes. Next, we explore the factors that directly influence the growth and depth of these roots, addressing elements such as soil type, climate, and water availability. Lastly, we investigate how the variation in <i>Eucalyptus</i> species may impact root growth patterns, biomass, and carbon stock. In this study, we observed that the maximum root depth increased by an average of 20% when genotypes were grown on sites with higher water availability (wet site). <i>E. urophylla</i> stands had a higher biomass and carbon stock (5.7 Mg C ha⁻¹) of fine roots when cultivated on dry sites (annual rainfall~727 mm) than the wet sites (annual rainfall~1590 mm). In <i>E. grandis</i> × <i>E. camaldulensis</i> stands, no significant differences were observed in the stock of fine root biomass (3.2 Mg C ha⁻¹) between the studied environments. Our results demonstrated that genotypes with greater drought tolerance (<i>E. grandis</i> × <i>E. camaldulensis</i>) tend to maintain higher stocks of fine root biomass (3.2–6.3 Mg ha⁻¹) compared to those classified as plastic (<i>E. urophylla</i>), regardless of the edaphoclimatic conditions of the cultivation site. Finally, our research helps understand how Eucalyptus trees adapt to their environment, aiding sustainable forest management and climate change mitigation. We also provide a practical tool to estimate underground biomass, assisting forest managers and policymakers in ensuring long-term forest sustainability.