The contribution of fog to water and nutrient supply to Arthraerua leubnitziae in the central Namib Desert, Namibia

摘要

Fog is a key source of moisture to the biota of the coastal Namib Desert and is associated with particulates that may contain essential nutrients for plants. Furthermore, fog makes dust deposited on leaves or on soil accessible for plant uptake. This study was carried out at five meteorological stations in the gravel plains of the central Namib Desert, along an east-west transect increasing in elevation inland. We hypothesised that marine-derived deposition contributes to moisture and nutrient supply of Arthraerua leubnitziae, an endemic shrub restricted to the fog zone of the central Namib Desert, and consequently determines its distribution. The range of A. leubnitziae, derived from a species distribution model, was found to coincide with areas with high fog occurrence, with fog contributing 36% to the modelled distribution of A. leubnitziae alongside precipitation (43%), iso-thermality (15%) and elevation (6%). We measured nutrients deposited in fog water derived from wet and dry deposition Ca2+, K+ Mg2+, Na+, Cl-, Br-, NO3-, PO43- and SO42- and plant essential nutrients in plant and soil samples (N, P, K, Ca, Mg, Mn, Fe, Cu and Zn). We also determined the nutrient uptake by stems of A. leubnitziae. Over the course of the sampling cycle, the total annual nutrient content of fog and dust was dominated by Ca2+ and Na+ Most of the nutrients (K+, Mg2+, Na+, and SO42-) were of marine origin. A. leubnitziae was found to be able to directly intercept and absorb some of the nutrients in the dust and fog via their stems. The low nutrient concentrations in the soils of the Namib Desert and significant inputs from dust and fog suggest deposition is an important source of nutrients for A. leubnitziae. We conclude that water and nutrients should not be considered separately in studying the role of fog as a determinant of plant distributions.