Stemflow Dynamics in the Jamari National Forest (Brazilian Amazon): II. Solute Concentrations and Flux Dynamics

Trees can redirect large volumes of rainwater to the base of their stems. This stemflow not only redistributes water but also channels canopy-derived solutes to the forest floor. Building on research showing canopy geometry and bark properties govern stemflow volumes, we examined how those same traits modulate the biogeochemical side of this flux. Over a 12-month period in Jamari National Forest (Brazil), we quantified stemflow volume and solute chemistry for 19 trees grouped by diameter at breast height (D: < 10, 10–20 and > 20 cm), crown area (CA: < 30, 30–60 and > 60 m2) and bark texture (smooth, fissured and rough). Small-stemmed, smooth-barked trees produced the greatest stemflow yields, whereas large-stemmed, rough-barked trees generated lower volumes but higher mean ion concentrations. Macronutrient-rich species appear to flip the usual water-flux story on its head. For example, calcium and potassium (two key nutrients for plant growth) rose sharply from 1.1 kg-Ca2+ ha−1 and 4.9 kg-K+ ha−1 in small, smooth-barked trees to 6.3 and 7.7 kg ha−1, respectively, in large rough-barked individuals. In contrast, trace anions such as chloride and bromide declined with size and roughness (Cl−: 1.3 to 0.4 kg ha−1; Br−: 0.20 to 0.03 kg ha−1). These contrasting patterns show that although small, smooth trees may dominate stemflow water routing, older, structurally complex trees disproportionately deliver the nutrients that drive forest productivity. Consequently, conserving structural diversity—including mature, rough-barked specimens—is essential for maintaining biogeochemical cycling in Amazonian forests threatened by deforestation and climate change.