Soil microbial inoculation during flood events shapes headwater stream microbial communities and diversity

Abstract

Flood events are now recognized as potentially important occasions for the transfer of soil microbes to stream ecosystems. Yet, little is known about these “dynamic pulses of microbial life” for stream bacterial community composition (BCC) and diversity. In this study, we explored the potential alteration of stream BCC by soil inoculation during high flow events in six pre-alpine first order streams and the larger Oberer Seebach. During 1 year, we compared variations of BCC in soil water, stream water and in benthic biofilms at different flow conditions (low to intermediate flows versus high flow). Bacterial diversity was lowest in biofilms, followed by soils and highest in headwater streams and the Oberer Seebach. In headwater streams, bacterial diversity was significantly higher during high flow, as compared to low flow (Shannon diversity: 7.6 versus 7.9 at low versus high flow, respectively, p < 0.001). Approximately 70% of the bacterial operational taxonomic units (OTUs) from streams and stream biofilms were the same as in soil water, while in the latter one third of the OTUs were specific to high flow conditions. These soil high-flow OTUs were also found in streams and biofilms at other times of the year. These results demonstrate the relevance of floods in generating short and reoccurring inoculation events for flowing waters. Moreover, they show that soil microbial inoculation during high flow enhances microbial diversity and shapes fluvial BCC even during low flow. Hence, soil microbial inoculation during floods could act as a previously overlooked driver of microbial diversity in headwater streams.

Bacterial communities in a subarctic stream network: Spatial and seasonal patterns of benthic biofilm and bacterioplankton

“…In all network positions, taxa that predominated the bacterioplankton community were characteristic freshwater species, and soil‐derived taxa mainly contributed to the diversity peak at the upmost headwater sites. These taxa apparently cross the land–water interface during exceptional rainfall events (Caillon et al, 2021 ; Cruaud et al, 2020 ), leading Wisnoski and Lennon ( 2021 ) to argue that local‐scale connectivity between terrestrial soils and bacterioplankton is in fact transient and relatively weak (see also Monard et al, 2016 ). By far most of the soil‐derived taxa are poorly adapted to freshwater life and are therefore rapidly filtered out from the aquatic species pool and/or remain metabolically inactive in the aquatic environment.…”

“…Bacterial communities in streams are assembled by a continuum of mechanisms along the riverine network, with headwater communities being controlled by the advection of bacteria from terrestrial soils (mass effects) while those in downstream sections are mainly driven by strong environmental selection (species sorting) (Crump et al, 2012 ; Hassell et al, 2018 ; Nelson et al, 2009 ; Niño‐García et al, 2016a ; Ruiz‐González et al, 2015 ). The land–water linkage is strongest at the upmost headwaters which receive high rates of soil‐derived immigrants, particularly during rainfall‐induced flood events (Caillon et al, 2021 ; Teachey et al, 2019 ). As water residence time (WRT) in headwaters is short, their bacterioplankton community composition probably reflects environmental sorting in the source habitat (e.g., soil pH or moisture) (Niño‐García et al, 2016a ).…”

“…Water temperature (Hullar et al, 2006 ; Teachey et al, 2019 ) and river discharge (Fortunato et al, 2012 ) are the key environmental factors reported to underlie seasonal variability in bacterial communities. Thus, in seasonally predictable environments, lotic communities tend to be highly stable at interannual scales but, at the same time, exhibit rapid turnover on weekly or even daily scales following abrupt environmental shifts in stream conditions (Caillon et al, 2021 ; Portillo et al, 2012 ; Veach et al, 2016 ).…”

Effect of Riparian Soil Moisture on Bacterial, Fungal and Plant Communities and Microbial Decomposition Rates in Boreal Stream-Side Forests

“…Implementing varying width buffers based on the occurrence of moist areas would be a straightforward approach to protect ecosystem functioning and riparian biodiversity. As aquatic biodiversity is linked to riparian microbial diversity (Caillon et al 2021, Koivusaari et al 2019, Ruiz-González et al, 2015, Judd et al 2006, implementing wet area -based buffers could help to maintain also aquatic diversity. However, we emphasize that the sufficiency of variable width buffer in maintaining diversity needs to be studied more specifically.…”

Fungal Diversity in Barley Under Different Storage Conditions

“…Compared with the above traditional techniques, high-throughput sequencing technologies with high flux, high sensitivity, and good accuracy can determine millions or even tens of millions of DNA sequences simultaneously in a short time range to cover a complex microbial community. The technology has been applied to analyze microbial communities in feces ( Holzhausen et al, 2021 ), fermented sausage ( Zhang et al, 2021a ), intestinal flora ( Bornbusch et al, 2021 ), and soil ( Caillon et al, 2021 ), and has been applied in medical science ( Li et al, 2021 ).…”