The impact of changing moisture conditions on short-term P availability in weathered soils

Background and Aims

Bioavailable phosphorus (P) represents a primary constraint on productivity in many ecosystems on highly-weathered soils. Soil moisture can be important to determining P bioavailability and net primary productivity in these systems. However, hydrologic controls on P availability remain poorly understood.

Methods

We used “resins” (anion-exchange membranes) to quantify the response of labile P, an estimate of bioavailable P, to soil moisture conditions in two highly-weathered soils (rendzina, ultisol). The resins were either incubated in soil or shaken with a soil-water slurry.

Results

Resin incubations in aerobic soil effectively quantified labile P in soils under changing moisture conditions, extracting significant amounts of labile P while avoiding the disturbance imposed by slurries. Wetting field-moist soils resulted in pulsed labile P, with lagged peaks occurring days after the largest moisture additions. Re-wetting air-dried soils enhanced labile P immediately, with the largest amounts observed at the highest moisture levels; labile P steadily declined following the moisture addition.

Conclusions

Soil moisture levels and history strongly impacted labile P, indicating the importance of both variables when interpreting labile P measurements. These results also suggest that P availability is linked to both the amount and timing of rainfall, with implications for plant productivity in regions exposed to changing moisture regimes.