Environmental degradation results in contrasting changes in the assembly processes of stream bacterial and fungal communities

Abstract

Environmental degradation may have strong effects on community assembly processes. We examined the assembly of bacterial and fungal communities in anthropogenically altered and near‐pristine streams. Using pyrosequencing of bacterial and fungal DNA from decomposed alder Alnus incana leaves, we specifically examined if environmental degradation deterministically decreases or increases the compositional turnover of bacterial and fungal communities. Our results showed that near‐pristine streams and anthropogenically altered streams supported distinct fungal and bacterial communities. The mechanisms assembling these communities were different in near‐pristine and altered environments. Environmental disturbance homogenized bacterial communities, whereas fungal communities were more dissimilar in disturbed sites than in near‐pristine sites. Compositional variation of both bacteria and fungi was related to water chemistry variables in disturbed sites, further implying the influence of environmental degradation on community assembly. Bacterial and fungal communities in near‐pristine streams were weakly controlled by environmental factors, suggesting that the relative importance of niche‐based versus neutral processes in assembling microbial communities may strongly depend on the spatial scale and local environmental context. Our results thus suggest that environmental degradation may strongly affect the composition and β‐diversity of stream microbial communities colonizing leaf litter, and that the direction of the change can be different between bacteria and fungi. A better understanding of the environmental tolerances of microbes and the mechanisms assembling microbial communities in natural environmental settings is needed to predict how environmental alteration is likely to affect microbial communities.

Abundant and Rare Bacterioplankton in Freshwater Lakes Subjected to Different Levels of Tourism Disturbances

“…Most studies did not differentiate the microbial community when exploring the diversity and composition of the microbial community in response to anthropogenic disturbances in aquatic ecosystems [25,26,52,53]. Considering possibly discrepant ecological roles in abundant and rare bacteria [31], we chose to divide the bacterioplankton community into two main components.…”

Beta diversity response to stress severity and heterogeneity in sensitive versus tolerant stream diatoms

“…Similarly, studies of macroinvertebrates and fungi have documented altered species prevalence, taxon loss, or decreased alpha diversity as explanations for increased beta diversity with stress or disturbance (Hawkins et al, ; Libório & Tanaka, ; Mykrä et al, ). Notably, Hawkins et al () observed greater heterogeneity across disturbed sites, in part attributed to low pH or unnaturally high pH relative to reference sites.…”

“…While initial perspectives on community assembly assumed that environmental determinism increases with stress (Chase, ), it is now evident that the effect of disturbance on environmental filtering is distinct to the taxon or system. For instance, Mykrä et al () reported that environmental degradation led to homogenization of bacterial communities but more stochastic fungal communities. Hawkins et al () observed more stochastic distribution of macroinvertebrates in intermediately disturbed sites, while severe disturbance generated physicochemical heterogeneity and more dissimilar taxonomic composition than predicted by chance.…”

“…Despite the expectation of reduced beta diversity in stressed systems, this negative trend is not always the case. At least a few studies have demonstrated an increase in beta diversity with stress or disturbance (Fugère, Kasangaki, & Chapman, 2016;Hawkins, Mykrä, Oksanen, & Vander Laan, 2015;Libório & Tanaka, 2016;Mykrä, Tolkkinen, & Heino, 2017). Reduced alpha diversity, loss of taxa, and decreased occupancy of once common species are often cited as explanations for this increase in beta diversity.…”

Pulling apart the urbanization axis: patterns of physiochemical degradation and biological response across stream ecosystems

“…In a synthesis of lotic microbial diversity studies, Zeglin (2015) found that microbial diversity was negatively affected by metals, temperature, substrate type, or hydrology more commonly than by more general effects of land use or nutrient concentrations. Chemical components of effluent inputs (Drury et al 2013) and other waterchemistry variables (Mykrä et al 2017) in urban streams can contribute to homogenization of bacterial communities. The interactions of urban influences are likely to simultaneously stress (e.g., increased peak flows, Cl 2 , SO 4 2-, heavy metals) and subsidize (e.g., increased nutrients, labile OM, temperature) microbial biomass and activity, thereby masking microbial response to urbanization.…”