The fog harvesting Namib Desert dune grass Stipagrostis sabulicola promotes niche building by modifying substrate and atmosphere conditions

Abstract

The fog harvesting grass Stipagrostis sabulicola is one of the few plants able to cope with the hostile conditions in dune fields of the hyper-arid Namib Desert. S. sabulicola tussocks modify the substrate and atmospheric conditions leading to the formation of fog plant oases (FPO). Average air temperature within FPO canopies was reduced by up to 7.5 °C and air humidity raised by 11 % compared to the bare sand, inducing a lowering of vapor pressure deficit (VPD) by up to 1.5 kPa. Stomatal conductance showed a negatitive correlation with VPD, rising to an average of 435 mmol.m-2 s-1 in the forenoon of foggy days. Due to leaf water runoff during fog events, substrate moisture at the plant basis increased locally to values of up to 16% ensuring adequate plant water supply during fogless days. FPO substrates had finer grain sizes and doubled concentration of organic particles, thus improving water storage capacity. Fog interception rate of the sand increased by up to 109 % with steepening of S. sabulicola mounds. Improved water availability, balanced temperature conditions and the presence of digestible plant material promote niche-building for substrate life, which in turn is a prerequisite for the functioning of fog-driven oases ecosystems.