Abstract
The invasion of ecosystems by strongly colonising plants such as Phragmites australis is viewed as one of the greatest threats to plant diversity and soil properties. This study compared a range of diversity measures including soil properties and mycorrhizal potential under different degrees of Phragmites density among three populations in coastal wetland, Victoria, Australia. Species richness, evenness and Shanon-Wiener index had significantly higher values in low degree of Phragmites density in all populations. Higher densities had the lowest diversity, with Shannon-Wiener index = 0 and Simpson’s index = 1 indicating its mono-specificity. Significant alterations in soil properties associated with different degrees of Phragmites density were noticed. These had interactive effects (population × density) on water content, dehydrogenase activity, microbial biomass (C, N and P) but not on pH, electrical conductivity, phenolics, organic carbon, and spore density. Furthermore, the study elucidated decrease of competitive abilities of native plants, by interfering with formation of mycorrhizal associations and biomass. Overall, our results suggest that significant ecological alterations in vegetation and soil variables (including mycorrhizal potential) were strongly dependent on Phragmites density. Such changes may lead to an important role in process of Phragmites invasion through disruption of functional relationships amongst those variables.
Highlights
Biological invasions by strongly competitive native and non-native species, is a worldwide phenomenon that threatens to dramatically change communities and ecosystems[1, 2]
The density of Phragmites shoots increased from none to maximal values over a distance of only 12 m (Fig. 1) and the density was significantly varied among invasion categories within each population (Kruskall-Wallis: χ2 = 13.62, 13.59 & 13.54 with df = 4 and p ≤ 0.05 for population 1, 2 & 3 respectively)
The diversity indices: species richness (S), Shannon-Wiener diversity index (H), species evenness (E) and Simpson’s reciprocal index (D−1) differed significantly among the density categories within each population (For example, in population_1: Kruskall-Wallis: χ2 = 13.27, 11.18, 11.28 & 11.01 with df = 4 and p ≤ 0.05 for S, H, E & D−1 respectively) but there were no significant differences among three populations (ANOVA: F2,42 = 2.45, 0.709, 0.095 & 0.550, p ≤ 0.05 for S, H, E & D−1 respectively)
Summary
Biological invasions by strongly competitive native and non-native species, (commonly referred to as invasive species), is a worldwide phenomenon that threatens to dramatically change communities and ecosystems[1, 2]. Many invasive species are tolerant of or even adapted to environmental disturbance, which is likely to accelerate their expansion[5] As a result, they often displace less competitive native species, resulting in the loss of plant diversity[1], which in turn, weakens the stability and functioning of ecosystems[6]. Topographic features of wetlands, such as their location in natural depressions and their frequent connectivity to both terrestrial and aquatic systems, make these ecosystems vulnerable to anthropogenic disturbances[8] These features can facilitate the invasion of both non-native and native plants. In this study, we examined how different degrees of invasion of a former Chaffy Saw Sedge (Gahnia filum) and Swamp Paperbark (Melaleuca ericifolia) coastal wetland dominated by Phragmites would affect community plant diversity and soil properties, including microbial with mycorrhizal potential
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