The Soil Bacterial Communities of South African Fynbos Riparian Ecosystems Invaded by Australian Acacia Species Etienne Slabbert 1 , Shayne Martin Jacobs 2 , Karin Jacobs 1 * 1 Department of Microbiology, Stellenbosch University, Stellenbosch, Western Cape, South Africa, 2 Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch, Western Cape, South Africa 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. Citation: Slabbert E, Jacobs SM, Jacobs K (2014) The Soil Bacterial Communities of South African Fynbos Riparian Ecosystems Invaded by Australian Acacia Species. PLoS ONE 9(1): e86560. doi:10.1371/journal.pone.0086560 Editor: Zaid Abdo, Institution and Department: Agricultural Research Service, United States of America Received June 6, 2013; Accepted December 11, 2013; Published January 24, 2014 Copyright: ß 2014 Slabbert et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This research was supported by the South African Water Research Commission (WRC) and the National Research Foundation (NRF). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: kj@sun.ac.za Introduction Riparian ecosystems are broadly classified as the interface between terrestrial and freshwater aquatic ecosystems [1,2,3]. Riparian ecosystems of the South African fynbos play a crucial role in the health and functioning of the diverse fynbos biome as a whole [4]. Fynbos riparian ecosystems have received very little scientific attention compared to the rest of the South African fynbos biome, although they have been shown to contribute disproportionately to ecological processes considering their rela- tively small land area [5,6,7]. These ecosystems are also the site of several important physical and biochemical processes [3,8]. Riparian ecosystems are unique in the landscape and often exhibit different rates of microbial mediated soil processes compared to upland areas [9]. 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]. Riparian ecosystems associated with the fynbos biome can be easily distinguished from the terrestrial fynbos based on hydrology, geomorphology and the structure of the vegetation [12,13]. The lateral zones commonly occurring in the fynbos riparian ecosys- tems are classified as the dry bank and wet bank zones [12] (Figure 1). The dry bank is infrequently inundated, typically only during periods of high flooding, which happen every few years [14]. The water from the river influences the dry bank in the form of ground water during low flow. In the upper catchments (the mountain fynbos riparian ecosystems), high flow and flooding is likely to occur during the rainy winter season [14]. On the other hand, the wet bank zones are classified as the area at the river’s edge, which is under constant influence of the river throughout the year, and is always likely to be moist to wet [12]. The importance of riparian ecosystems and associated plant and microbial biota are now becoming clear due to the increased degradation of riparian ecosystems worldwide [15], [16]. The riparian ecosystems of the Western Cape fynbos biome are largely degraded due to the invasion of non-native A. mearnsii and A. longifolia originating from Australia [17] which have, to a large extent, displaced the native riparian vegetation [18]. Acacia species such as A. saligna, have been shown to be associated with nitrogen- fixing bacteria, which may have a dramatic effect on soil nitrogen stocks and soil microbial community structure [15,19]. The recovery of the native fynbos vegetation occurs very slowly where Acacias are cleared [20,21]. This poor recovery sparked interest in the soil dynamics of the fynbos riparian ecosystems, and it has been suggested that soil microbial dynamics may have been PLOS ONE | www.plosone.org 1 January 2014 | Volume 9 | Issue 1 | e86560