Abstract:
Despite the dominance of microorganisms in arid soils, the structures and functional dynamics
of microbial communities in hot deserts remain largely unresolved. The effects of wetting event
frequency and intensity on Namib Desert microbial communities from two soils with different
water-regime histories were tested over 36 days. A total of 168 soil microcosms received wetting
events mimicking fog, light rain and heavy rainfall, with a parallel “dry condition” control. T-RFLP
data showed that the different wetting events affected desert microbial community structures, but
these effects were attenuated by the effects related to the long-term adaptation of both fungal
and bacterial communities to soil origins (i.e. soil water regime histories). The intensity of the water
pulses (i.e. the amount of water added) rather than the frequency of wetting events had greatest
effect in shaping bacterial and fungal community structures. In contrast to microbial diversity,
microbial activities (enzyme activities) showed very little response to the wetting events and were
mainly driven by soil origin. This experiment clearly demonstrates the complexity of microbial
community responses to wetting events in hyperarid hot desert soil ecosystems and underlines the
dynamism of their indigenous microbial communities.
