Canopy processing of atmospheric dust creates a short-term phosphorus pathway in a tropical forest

Abstract. Phosphorus (P) availability constrains productivity in many humid tropical forests, where highly weathered soils retain P in poorly available forms and external inputs are needed to offset long-term losses. Caribbean forests receive new P through trans-Atlantic Saharan dust and episodic African biomass-burning particles, however how this particulate P enters forest nutrient cycling remains poorly understood. Here, we examined the fate and uptake of particulate P in the Luquillo Experimental Forest, Puerto Rico, using a foliar dust-application experiment and soil incubations with mineral dust and wildfire ash. In soils, both materials increased P supply to ion-exchange membranes, but mineral dust-derived P was rapidly transferred into Fe- and Al-associated pools, whereas wildfire ash generated greater short-term P availability. On leaves, mineral dust exposure resulted in foliar uptake of dust-derived Fe and P, with P uptake quantified using Fe as a conservative anchor. Particles recovered from leaf surfaces contained more bicarbonate-extractable P than the applied dust, indicating that contact with leaves increased the lability of P remaining in deposited particles. Together, these findings identify two complementary canopy pathways: direct foliar uptake of dust-derived P and leaf-surface processing that increases the fraction potentially available for subsequent uptake, either from foliage or, following redistribution in throughfall, by roots. By revealing a pre-soil pathway for atmospheric P, our results highlight a process not explicitly represented in most terrestrial nutrient-cycle frameworks that may affect how models represent the biological availability of dust-derived P and its coupling to tropical forest carbon cycling.