The Soil Bacterial Communities of South African Fynbos Riparian Ecosystems Invaded by Australian <i>Acacia</i> Species

<div><p>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 <i>Acacia mearnsii, A. saligna</i> and <i>A. dealbata</i>. 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 <i>Acacia</i> invasion. The presence of invasive <i>Acacia</i> was correlated with specific bacterial phyla. However, high similarity between cleared and pristine sites suggests that the effect of <i>Acacia</i> 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 <i>Acacia</i> invasion on these communities.</p></div

The terrestrial (squares) and dry bank (triangles) form a cluster, which samples showed under dispersion (measured with BETADISP).

<p>The terrestrial (squares) and dry bank (triangles) form a cluster, which samples showed under dispersion (measured with BETADISP).</p

Location of sampling sites with invaded sites indicated in red, cleared sites in blue and pristine sites in green.

<p>2a: Natural riparian vegetation at the lower Eerste River site. 2b: Cleared riparian zone from the Sir Lowry’s and 2c: Riparian zones invaded by Acacia mearnsii at the lower Jakkals River site.</p

The Shannon’s diversity index based on the bacterial ARISA profiles comparing natural, cleared and invaded lateral zones for all three seasons.

<p>The interaction effect between hydrological zones and the invasive status was significant (F = 2.7191, p = .00580).</p

Schematic representation of the lateral zones of the riparian sites and the positions of the sample plots.

<p>The extent of each lateral zone is variable depending on the specific dimensions of the riparian zone but ranged from 2m to 10m wide.</p

a: The indicator values of the indicator phyla in the community between lateral zones (p<0.05). b: The indicator values and the relative abundance of the indicator phyla in the community when comparing invasive status (p<0.05).

<p>a: The indicator values of the indicator phyla in the community between lateral zones (p<0.05). b: The indicator values and the relative abundance of the indicator phyla in the community when comparing invasive status (p<0.05).</p

R values of the ANOSIM comparisons made between hydrological zones and invasion status within dry bank and wet bank zones.

<p>Non-significant p values >0.05 are indicated by an asterisk.</p

Non-metric multi-dimensional scaling ordination plot of the distance between bacterial communities based on the Bray-Curtis distance.

<p>The ellipses represent the samples which were within 75% confidence limit of the centroids and included the wet bank (circles), dry bank (triangles) and the terrestrial samples (squares) (Stress = 0.12).</p

Characterization of Alkylsilane Self-Assembled Monolayers by Molecular Simulation

Self-assembled monolayers (SAM) of dodecyltrichlorosilane (DTS) and octadecyltrichlorosilane (OTS) on silica are studied by molecular dynamics simulations at 298 K and 1 bar. The coverage (number of alkylsilane molecules per surface area) is systematically varied. The results yield insight into the properties of the alkylsilane SAMs, which complement experimental studies from the literature. Relationships are reported between thickness, tilt angle, and coverage of alkylsilane SAMs, which also hold for alkylsilanes other than DTS and OTS. They are interpreted based on the information on molecular ordering in the SAMs taken form the simulation data. System size and simulation time are much larger than in most former simulation works on the topic. This reduces the influence of the initial configuration as well as the periodic boundary conditions and hence minimizes the risk of artificial ordering. At the same time, more reliable statistics for the calculated properties can be provided. The evaluation of experimental data in the field is often based on strongly simplified models. The present simulation results suggest that some of these lead to errors, concerning the interpretation of experimental results, which could be avoided by introducing more realistic models

The diversity of <i>Trichoderma</i> species from soil in South Africa, with five new additions

<p>Fourteen <i>Trichoderma</i> (Hypocreales) species were identified during a survey of the genus in South Africa. These include <i>T. afroharzianum, T. asperelloides, T. asperellum, T. atrobrunneum, T. atroviride, T. camerunense, T. gamsii, T. hamatum, T. koningii, T. koningiopsis, T. saturnisporum, T. spirale, T. virens</i>, and <i>T. viride</i>. Ten of these species were not known to occur in South Africa prior to this investigation. Five additional species were novel and are described here as <i>T. beinartii, T. caeruleimontis, T. chetii, T. restrictum</i>, and <i>T. undulatum</i>. These novel <i>Trichoderma</i> species display morphological traits that are typical of the genus. Based on molecular identification using calmodulin, endochitinase, nuc rDNA internal transcribed spacers (ITS1-5.8S-ITS2), RNA polymerase II subunit B, and translation elongation factor 1-α gene sequence data, <i>T. beinartii, T. caeruleimontis</i>, and <i>T. chetii</i> were found to belong to the <i>Longibrachiatum</i> clade, whereas <i>T. restrictum</i> is a member of the <i>Hamatum</i> clade. <i>Trichoderma undulatum</i> occupies a distinct lineage distantly related to other <i>Trichoderma</i> species. Strains of <i>T. beinartii</i> and <i>T. chetii</i> were isolated previously in Hawaii and Israel; however, <i>T. caeruleimontis, T. restrictum</i>, and <i>T. undulatum</i> are so far known only from South Africa.</p