Non-Rainfall Moisture Activates Fungal Decomposition of Surface Litter in the Namib Sand Sea

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.

High night‐time humidity and dissolved organic carbon content support rapid decomposition of standing litter in a semi‐arid landscape

“…; Jacobson et al . ). Indeed, we found that the microbial respiration rate at 06.00 h in the morning was positively associated with the litter moisture content at the same time during the measured dates (Fig.…”

“…Compared with microbes in soils, microbes in standing litter often experience a drier daytime microclimate and greater temperature fluctuations (King, Brandt & Adair ; Lin & King ; Jacobson et al . ). Those conditions could restrict microbial activity on standing litter and therefore affect biological decomposition.…”

Measurements and ecological implications of non‐rainfall water in desert ecosystems—A review

“…This may stem from the fact that the ionic composition of both dew and fog is generally higher than that of rain. While playing a positive role in plant growth by nutrient contribution, dew was also reported to increase litter decomposition (Dirks et al, 2010;Jacobson et al, 2015;Kuehn, Steiner, & Gessner, 2004;Newell, Fallon, Rodriguez, & Groene, 1985), playing an important role in nutrient mineralization and cycling. Dew and fog were found to serve as fertilizer for lithobionts (Kidron & Starinsky, 2012), and plants (Dasch, 1988;Katz et al, 1989;Kobayashi et al, 2002;Xu et al, 2013).…”

Fog Spatial Distributions over the Central Namib Desert - An Isotope Approach

“…It is often assumed that fog in these coastal regions is advected from the ocean and the majority of authors agree that advective sea fog dominates the south-west coast of Africa (Seely, 1979;Olivier, 2004;Jacobson et al, 2015). The most visible impacts of this advective fog on ecophysiology in the Namib Desert are thought to extend about 60 km inland, a region known as the fog-zone (Seely, 1979;Lancaster, 1984;Olivier, 1995).…”