'University of Pretoria - Department of Philosophy'
Abstract
Deserts are the largest terrestrial ecosystem (Laity, 2009). It is estimated that 69% of desert lands
that are used for agriculture around the world are either degraded or undergoing desertification as
a consequence of climatic variation or intensive human activity (UNEP, 1992; Souvignet et al.,
2012). Additionally, climate change models predict that the variability of rainfall events will
intensify in desert regions (Faramarzi et al., 2013). Because desert environments contain a limited
range of higher plants and animals, soil microbial communities are likely the most productive
component of these systems as well as the dominant drivers of biogeochemical cycling
(Makhalanyane et al., 2015). As a result, understanding how microbial communities respond to
varying degrees of moisture input and xeric stress is important for developing sustainable resource
management and agriculture practices, as well as predicting the impacts of global climate change
on terrestrial systems (Paul, 2014).
This study focuses on the Namib Desert in western Namibia, the oldest and one of the driest deserts
on the planet (Prestel et al., 2008). In the Namib Desert, sporadic rainfall events provide 25 mm of
mean annual rainfall a year; however, near the coast, consistent fog formation provides a form of
available water to an area that would otherwise be hyperarid (Eckardt et al., 2013b). We examined
the effect of xeric stress on microbial community structure and function in these desert soils,
taking advantage of the naturally occurring gradient of water availability. Soil samples were
collected every 10 km on a 190 km transect from the fog-dominated coastal region, through an
inland area of high aridity, into a region of increased rainfall. Soil physicochemical properties and
microbial community structure and function were assessed across the transect.
Both microbial community structures and functions differentiated based on three a priori defined
zones of differing xeric stress (i.e., the Fog , Dry , and Rain zones). Water availability was
indicated as significantly shaping the microbial community structure and function in the central
Namib Desert. In the fog dominated regions, stochastic processes dominated community assembly,
while the deterministic effects of environmental filtering shaped community structure in the rest of
the transect. In addition, a significant relationship between community structure and function was
found (Mantel r = 0.2; p < 0.01), indicating changes in community structure coincided with changes
in function.Dissertation (MSc)--University of Pretoria, 2016.tm2016Microbiology and Plant PathologyMScUnrestricte
