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, Zn, and others. 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 particles separately on a plant’s foliage or onto its roots. We conducted experiments on chickpea model plants under ambient and elevated CO₂ levels, 412 and 850 ppm, that reflect current and future climate scenarios. We found that plants can uptake fire ash P only through their leaves, by a direct nutrient uptake from particles captured on their foliage, but not via their roots. In a future climate scenario, foliar nutrient uptake pathway may be even more significant for plants, due to the partial inhibition of key root uptake mechanism. Our findings highlight the effectiveness of the foliar nutrient uptake mechanism under both ambient and elevated CO₂ levels, with fire ash P being the sole nutrient absorbed by the foliage. These findings demonstrate the substantial contribution of fire ash to the nutrition of plants. 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.