Habitat differentiation of diverse tropical tree species is supported by different root strategies of nutrient acquisition from the highly weathered soils. In the rhizosphere (soil affected by roots), tree species modify carbon (C) and nutrient cycles directly through root exudation and indirectly through increased microbial activity. We test whether root exudation and rhizosphere C fluxes of organic acids and sugars differ between dominant dipterocarp trees and pioneer trees (Macaranga gigantea). To quantify the C fluxes of organic acids in the rhizosphere soils, we measured in situ root exudation from mature trees, concentrations of organic acids (acetate, oxalate, malate, and citrate) and monosaccharides in the rhizosphere and bulk soil fractions, and mineralization kinetics of ¹⁴C-radiolabelled substrates. Dipterocarp roots release greater amounts of malate than pioneer tree roots, while monosaccharides are dominant exudates of pioneer trees. Organic acid exudation increases with increasing root surface area and with decreasing soil pH. Microbial activities of malate mineralization are enhanced in the rhizosphere both under Dipterocarp and Macaranga trees, but the C fluxes of malate mineralization by rhizosphere microbes exceeded root exudation due to microbial malate production in rhizosphere of Dipterocarp trees. Tree species affects both root exudation composition and rhizosphere microbe activities that increase malate production at lower soil pH, likely for phosphorus solubilization, aluminum detoxification, and lignin degradation.