Phosphorus input through fog deposition in a dry tropical forest

In many tropical forests, where phosphorus (P) is considered a limiting nutrient, atmospheric deposition can contribute significantly to available P. Previous studies have shown that P inputs from atmospheric deposition are enhanced by plant canopies. This effect is explained as the result of increased deposition of P-rich aerosol particles (dry deposition) and fog droplets (fog or occult deposition) onto leaf surfaces. Here we studied the importance of fog as a source of P to a P-limited dry tropical forest. Throughout an 80 day period during the dry season when fog is most common, we sampled fog water and bulk precipitation in a clearing and measured leaf wetness and throughfall in an adjacent secondary and mature forest stand. During the study period, total P (P-T) concentrations in fog water ranged from 0.15 to 6.40mg/L, on average fourteenfold greater than P-T concentrations in bulk precipitation (0.011 to 0.451mg/L), and sixfold and sevenfold greater than throughfall P-T concentrations in the secondary and mature forest stands, respectively (0.007 to 1.319mg/L; 0.009 to 0.443mg/L). Based on leaf area index, the frequency of fog deposition, and amount of water deposited per fog event, we estimate that fog delivers a maximum of 1.01kg/ha/yr to secondary forest stands and 1.75kg/ha/yr to mature forest stands, compared to 0.88kg/ha/yr to secondary forest stands and 1.98kg/ha/yr to mature forest stands via throughfall (wet+dry deposition) and stemflow. Thus, fog deposition may contribute substantially to available P in tropical dry forests.