Tropical tree species traits drive soil cation dynamics via effects on pH: a proposed conceptual framework

Humid tropical forests are major players in the global carbon cycle, despite evidence that cations (rock-derived, positively charged ions) can limit or co-limit net primary productivity (NPP). In mature forests, tight cation cycling, i.e., without leaching losses, could maintain cation stocks on site. That mechanism does not explain how regenerating tropical secondary forest trees start from seeds and accrue large cation stocks in biomass, when growing on soils depleted in available cations. We propose a new mechanism that links tree species’ traits to soil cation availability via impacts on soil pH, a ‘master’ biogeochemical driver. We tested plot-level effects of tree species on soil pH, soil extractable cations, and cation accrual in biomass in a unique, 25-yr-old, randomized-complete-block experiment in which climate, soil, and previous land-use history were similar across four native tree species grown in mono-dominant plantations in Costa Rica. Surface-soil pH in this Oxisol, init...