Microbial diversity in an intensively managed landscape is structured by landscape connectivity

Abstract

Intensively managed land increases the rate of nutrient and particle transport within a basin, but the impact of these changes on microbial community assembly patterns at the basin scale is not yet understood. The objective of this study was to investigate how landscape connectivity and dispersal impacts microbial diversity in an agricultural-dominated watershed. We characterized soil, sediment and water microbial communities along the Upper Sangamon River basin in Illinois-a 3600 km2 watershed strongly influenced by human activity, especially landscape modification and extensive fertilization for agriculture. We employed statistical and network analyses to reveal the microbial community structure and interactions in the critical zone (water, soil and sediment media). Using a Bayesian source tracking approach, we predicted microbial community connectivity within and between the environments. We identified strong connectivity within environments (up to 85.4 ± 13.3% of sequences in downstream water samples sourced from upstream samples, and 44.7 ± 26.6% in soil and sediment samples), but negligible connectivity across environments, which indicates that microbial dispersal was successful within but not between environments. Species sorting based on sample media type and environmental parameters was the dominant driver of community dissimilarity. Finally, we constructed operational taxonomic unit association networks for each environment and identified a number of co-occurrence relationships that were shared between habitats, suggesting that these are likely to be ecologically significant.

Connecting through space and time: catchment‐scale distributions of bacteria in soil, stream water and sediment

“…Our study showed weaker connectivity between the terrestrial and aquatic environments than has been shown elsewhere (Crump et al ., ; Ruiz‐González et al ., ; Griffin et al ., ). Our sampling scale was sufficient to detect spatial changes in soil microbial communities (Fig.…”

“…Our study provides new insights into the connectivity between bacterial communities in soil, stream water and stream sediments at small spatial scales (~1 m–1 km), building on previous knowledge obtained at much larger spatial scales (Crump et al ., ; Ruiz‐González et al ., ; Griffin et al ., ). Through intensive sampling of the soil, stream water and stream sediment in a native forest catchment, we have shown that, while the microbial communities in these different habitats are distinct from one another, there appears to be a degree of connectivity among them all, but the proportion of shared taxa varies by habitat combination.…”

“…These differences could be due to the level of catchment homogenization caused by the intensive landscape management in the river basin that Griffin et al . () sampled, compared with our native forest catchment, which was environmentally heterogeneous. Combining data from multiple catchments will be an essential next step to further develop our knowledge on what shapes microbial communities across ecosystems.…”

“…Griffin et al . () showed that over large spatial scales, bacterial community similarity was greater within habitat types than between when comparing soil and stream water, or stream water and sediment. Interestingly, in their study, the bacterial communities in soil and sediment samples were indistinguishable from each other.…”

“…Griffin et al . () showed, through surveying a 3600 km 2 catchment with 77 soil, sediment and stream water samples, that bacterial communities present in downstream water were highly connected to those present in upstream water, and connected to a lesser extent to upstream soil and sediment communities. In boreal ecosystems, bacterial communities in freshwater streams and lakes were shown to have a common terrestrial source, and terrestrially derived taxa dominated the communities when analysing ~200 terrestrial and aquatic samples from a ~19 000‐km 2 catchment (Ruiz‐González et al ., ).…”