Abstract
The hyper-arid western Namib Sand Sea (mean annual rainfall 0–17 mm) is a detritus-based ecosystem in which primary production is driven by large, but infrequent rainfall events. A diverse Namib detritivore community is sustained by minimal moisture inputs from rain and fog. The decomposition of plant material in the Namib Sand Sea (NSS) has long been assumed to be the province of these detritivores, with beetles and termites alone accounting for the majority of litter losses. We have found that a mesophilic Ascomycete community, which responds within minutes to moisture availability, is present on litter of the perennial Namib dune grass Stipagrostis sabulicola. Important fungal traits that allow survival and decomposition in this hyper-arid environment with intense desiccation, temperature and UV radiation stress are darkly-pigmented hyphae, a thermal range that includes the relatively low temperature experienced during fog and dew, and an ability to survive daily thermal and desiccation stress at temperatures as high as 50°C for five hours. While rainfall is very limited in this area, fog and high humidity provide regular periods (≥ 1 hour) of sufficient moisture that can wet substrates and hence allow fungal growth on average every 3 days. Furthermore, these fungi reduce the C/N ratio of the litter by a factor of two and thus detritivores, like the termite Psammotermes allocerus, favor fungal-infected litter parts. Our studies show that despite the hyper-aridity of the NSS, fungi are a key component of energy flow and biogeochemical cycling that should be accounted for in models addressing how the NSS ecosystem will respond to projected climate changes which may alter precipitation, dew and fog regimes.
Highlights
Across all ecosystems, the proportion of primary production that is consumed as litter, rather than actively-transpiring vegetation is estimated to be as high as 50–99% [1]
Of the total annual precipitation recorded during our 7-year period of analysis, 84% was derived from fog in events averaging 1.4 mm on 88% of the days during which precipitation occurred
Our meteorological analysis shows that small precipitating fog and rainfall events of 1–2 mm that could wet the substrates in the same manner as our wetting experiments occur on average every 6–7 days, making these small moisture inputs a regular source of usable moisture for doi:10.1371/journal.pone.0126977.g007
Summary
The proportion of primary production that is consumed as litter, rather than actively-transpiring vegetation is estimated to be as high as 50–99% [1]. A year after a significant rain pulse, 92–94% of the resulting vegetation biomass is wind-blown detritus that sustains detritivores over a multi-year period [5,6]. These detritivores (e.g. termites, tenebrionid beetles, microarthropods and ants) feed a diverse array of higher trophic levels of arachnids, reptiles, small mammals and birds [5,7]. Water collects on leaning grass stems and inflorescences (Fig 1C) and drips to the sand surface where it may be consumed by beetles and reptiles
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
