Abstract
Riparian ecosystem along rivers and streams are characterised by lateral and longitudinal ecological gradients and, as a result, harbour unique biodiversity. Riparian ecosystems in the fynbos of the Western Cape, South Africa, are characterised by seasonal dynamics, with summer droughts followed by high flows during winter. The unique hydrology and geomorphology of riparian ecosystems play an important role in shaping these ecosystems. The riparian vegetation in the Western Cape has, however, largely been degraded due to the invasion of non-indigenous plants, in particular Acacia mearnsii, A. saligna and A. dealbata. This study investigated the effect of hydrology and invasion on the bacterial communities associated with fynbos riparian ecosystems. Bacterial communities were characterised with automated ribosomal intergenic spacer analysis (ARISA) and 454 16S rDNA pyrosequencing. Chemical and physical properties of soil within sites were also determined and correlated with community data. Sectioning across the lateral zones revealed significant differences in community composition, and the specific bacterial taxa influenced. Results also showed that the bacterial community structure could be linked to Acacia invasion. The presence of invasive Acacia was correlated with specific bacterial phyla. However, high similarity between cleared and pristine sites suggests that the effect of Acacia on the soil bacterial community structure may not be permanent. This study demonstrates how soil bacterial communities are influenced by hydrological gradients associated with riparian ecosystems and the impact of Acacia invasion on these communities.
Highlights
Riparian ecosystems are broadly classified as the interface between terrestrial and freshwater aquatic ecosystems [1,2,3]
The results from the two factorial ANOVA, showed that the bacterial diversity of the wet bank zones were significantly lower (p,0.05) when Acacia invasion occurred (Figure 3). This decreased diversity was observed with the pyrosequencing data, which showed a significantly lower Shannon diversity index in the invaded wet bank zones according to Kruskal-Wallis ANOVA (F = 2.54, p = 0.048) (Figure S1)
PERMADISP dispersions showed that no significant differences in dispersion occurred between sites, a significant difference in dispersal occurred between the different lateral zones
Summary
Riparian ecosystems are broadly classified as the interface between terrestrial and freshwater aquatic ecosystems [1,2,3]. Fynbos riparian ecosystems have received very little scientific attention compared to the rest of the South African fynbos biome, they have been shown to contribute disproportionately to ecological processes considering their relatively small land area [5,6,7]. These ecosystems are the site of several important physical and biochemical processes [3,8]. The most important ecosystem service provided by riparian ecosystems is the supply of clean water, which is greatly, influenced by soil microbial processes [10,11]
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