Chac´on, N., Silver, W.L., Dubinsky, E.A. & Cusack, D.F. 2006. Iron
reduction and soil phosphorus solubilization in humid tropical forest
soils: the roles of labile carbon pools and an electron shuttle compound.
Biogeochemistry, 78, 67–84.
The affinity of iron oxides and hydroxides for phosphorus is thought to contribute to
phosphorus limitation to net primary productivity in humid tropical forests on acidic, highly
weathered soils. Perennially warm, humid conditions and high biological activity in these soils can
result in fluctuating redox potential that in turn leads to considerable iron reduction in the presence
of labile carbon and humic substances. We investigated the effects of reducing conditions in
combination with the addition of labile carbon substrates (glucose and acetate) and an electron
shuttle compound on iron reduction and phosphorus release in a humid tropical forest soil. Glucose
or acetate was added to soils as a single dose at the beginning of the experiment, and as pulsed
inputs over time, which more closely mimics patterns in labile carbon availability. Iron reduction
and phosphorus mobilization were weakly stimulated by a single low level addition of carbon, and
the addition of the electron shuttle compound with or without added carbon. Pulsed labile carbon
additions produced a significant increase in soil pH, soluble iron, and phosphorus concentrations.
Pulsed labile carbon inputs also promoted the precipitation of ferrous hydroxide complexes which
could increase the capacity for P sorption, although our results suggest that rates of P solubilization
exceeded re-adsorption. Plant and microbial P demand are also likely to serve as an important sinks
for released P, limiting the role of P re-adsorption. Our results suggest that reducing conditions
coupled with periodic carbon inputs can stimulate iron reduction and a corresponding increase in
soil phosphorus mobilization, which may provide a source of phosphorus to plants and microorganisms
previously undocumented in these ecosystems.