Direct foliar uptake of phosphorus from desert dust

Abstract

Phosphorus (P) scarcity constrains plant growth in many ecosystems worldwide. In P-poor ecosystems, the biogeochemical paradigm links plant productivity with the deposition of P-rich dust originating from desert storms. However, dust P usually has low bioavailability and is thought to be utilized solely via roots. We applied desert dust on the leaf surface of P-deficient and P-sufficient wheat, chickpea and maize to test the feasibility of direct foliar uptake of dust-P and investigate its related acquisition mechanisms. Foliar dust doubled the growth of P-deficient chickpea and wheat, crops originating near the Syrian Desert. P deficiency stimulated several leaf modifications that enabled acquisition of up to 30% of the sparingly soluble dust-P that is conventionally perceived as unavailable. These modifications increased foliar dust capture, acidified the leaf surface and, in chickpea, enhanced exudation of P-solubilizing organic acids. Maize (originating far from deserts) displayed only a marginal response to dust. The dramatic response of chickpea and wheat in comparison to maize suggests that plants that evolved in dust-rich ecosystems adopted specialized utilization strategies. Interestingly, the abovementioned foliar responses are comparable to known P uptake root responses. Given that P limitation is almost universal, a foliar P uptake pathway will have significant ecological and agricultural implications.

Keywords: desert dust; foliar uptake; leaf surface; organic exudates; phosphorus; plant nutrition.