Abstract. The strong phosphorus (P) sorption capacity of iron (Fe)
and aluminum (Al) minerals in highly weathered, acidic soils of humid
tropical forests is generally assumed to be an important driver of P
limitation to plants and microbial activity in these ecosystems. Humid
tropical forest soils often experience fluctuating redox conditions that
reduce Fe and raise pH. It is commonly thought that Fe reduction generally
decreases the capacity and strength of P sorption. Here we examined the
effects of 14 d oxic and anoxic incubations on soil P sorption dynamics in
humid tropical forest soils from Puerto Rico. Contrary to the conventional
belief, soil P sorption capacity did not decrease under anoxic conditions,
suggesting that soil minerals remain strong P sinks even under reducing
conditions. Sorption of P occurred very rapidly in these soils, with at
least 60 % of the added P disappearing from the solution within 6 h.
Estimated P sorption capacities were much higher, often by an order of
magnitude, than the soil total P contents. However, the strength of P
sorption under reducing conditions was weaker, as indicated by the increased
solubility of sorbed P in NaHCO3 solution. Our results show that highly
weathered soil minerals can retain P even under anoxic conditions, where it
might otherwise be susceptible to leaching. Anoxic events can also
potentially increase P bioavailability by decreasing the strength, rather
than the capacity, of P sorption. These results improve our understanding of
the redox effects on biogeochemical cycling in tropical forests.
Supplementary material to "Anoxic conditions maintained high phosphorus sorption in humid tropical forest soils"
