Direct foliar phosphorus uptake from wildfire ash

Abstract

Atmospheric particles originating from combustion byproducts (burned biomass or wildfire ash) are highly enriched in nutrients such as P, K, Ca, Mg, Fe, Mn, and Zn. Over long timescales, deposited wildfire ash particles contribute to soil fertility by replenishing soil nutrient reservoirs. However, the immediate nutritional effects of freshly deposited fire ash on plants are mostly unknown. Here, we study the influence of fire ash on plant nutrition by applying ash separately on a plant's foliage or to its substrate around the roots. We conducted experiments on chickpea model plants under ambient and elevated CO2 levels, which reflect current and future climate scenarios. We found that plants can utilize fire ash P and Ni through their leaves by direct nutrient uptake from particles captured on their foliage but not via their roots, both under ambient and elevated CO2 levels. These results indicate that over a short timescale, plants effectively uptake P from fire ash only via the foliage rather than the root pathway, which is possibly due to low bioavailability or limited contact between fire ash particles and the roots. According to many previous studies, elevated levels of CO2 will reduce the ionome of plants due to the partial inhibition of the key root uptake mechanism, thus increasing the significance of foliar nutrient uptake in a future climate. Furthermore, the role of fire ash is expected to increase in the future world, thus giving a competitive advantage to plants that can utilize fire ash P from the foliar pathway, as fire ash P is a particularly efficient and important source of P.