Chemical processes in receiving soils accelerate solubilisation of phosphorus from desert dust and fire ash

Abstract

AbstractAtmospheric deposition of desert dust and ash from wildfires are recognised as major suppliers of phosphorus (P) to soils in many terrestrial ecosystems. The biological effects of desert dust and fire ash P depend on their interactions with the receiving soils. However, the chemical processes and environmental conditions that control dust and ash P bioavailability post deposition are unknown. Soil and rhizospheric pH and organic exudates are acknowledged as central parameters that control soil P bioavailability. Here we performed a series of in‐vitro incubation experiments to study their effects on P solubility of various desert dust and fire ash samples. Then, we tested the dust and ash P solubility that were added to acidic and alkaline soils. Our results show that dust P solubility gradually increases by a few orders of magnitude as pH decreases from 7 to 2.5 and also with increased concentrations of oxalic and malic acids, two ubiquitous P solubilising organic exudates in soils. In both cases, the increase in dust P solubility occurs mainly by dissolving P from insoluble Ca‐P minerals such as apatite, the major P bearing mineral in desert dust. P solubility of fire ash was dramatically higher than that of desert dust but showed the same pattern of a gradual increase with decreasing pH or with increasing concentrations of oxalic and malic acids. When the dust was suspended with soils, extractable P level was ~10 times higher in alkaline soil than acidic soil despite the lower pH of the later, probably due to the strong P sorption capacity of the acidic soils. On the contrary, when fire ash was suspended, extractable P in the acidic soil was higher than that of the alkaline soil indicating substantial variation in P forms. Overall, our results indicate that the bioavailability of P from desert dust and fire ash is largely controlled by environmental and chemical factors in the receiving soils.Highlights Atmospheric deposition from desert dust and fire ash is a major phosphorus source to soils. However, the actual bioavailability of dust and ash P post deposition is unknown. Soil pH, organic acids concentrations and P sorption capacity controls dust and ash bioavailability. The bioavailability of atmospheric P is controlled by environmental factors in the receiving soils.