Attributes of Drying Define the Structure and Functioning of Microbial Communities in Temperate Riverbed Sediment

Abstract

Combined effects of climate change and increasing anthropogenic water demand have increased and extended dry period occurrences in rivers worldwide. Riverbed drying can significantly affect sediment microorganisms, crucial drivers of biogeochemical processes in lotic systems. In this study, we evaluated how sediment bacterial and fungal community structure and composition (based on 16S rRNA gene and ITS metabarcoding) and microbial functions (community respiration and extracellular enzymatic activities) respond to different riverbed drying intensities over 90 days. Riverbed sediment collected in a flowing reach of the Spree river in northeastern Germany was dried under different rates in outdoor mesocosms during the summer months of 2018. Our results demonstrate that drying attributes (duration and intensity) and sediment organic matter (OM) content play a crucial role in sediment microbial community assembly and functioning throughout drying. Milder drying surprisingly triggered a more rapid and drastic change in the microbial community composition and diversity. After 90 days of drying, Bacilli (Firmicutes) became the dominant bacterial class in most treatments, except in sediments with low OM content under the most severe drying treatment. Fungal amplicon sequence variants (ASVs) from Dothideomycetes (Ascomycota) had by far the highest relative abundance in all our treatments at the end of the drying experiment, making up 65.1% to 94.0% of the fungal reads. CO2 fluxes, a proxy for sediment community respiration, were rapidly and strongly affected by drying in all treatments. Our results imply that even short riverbed drying periods are likely to have significant consequences for the biogeochemical dynamics in recently formed non-perennial temperate rivers.

Long-term functional recovery and associated microbial community structure after sediment drying and bedform migration

“…being the species with the highest deviation from the control (1.6-fold increased abundance). When looking at relative abundance, Dothideomycetes were initially the most dominant fungal group in dried sediments (in concordance with Schreckinger et al, 2021), but their relative abundance decreased with increasing recovery time (Supplementary Figure S5).…”

“…To prepare the dried sediment, we sampled fully submerged and immobile (hereafter stationary) sandy sediment from the top 10 cm of the riverbed in June 2018 (Supplementary Figures S2A,B). The sediment was dried for 90 days under an outdoor translucent rooftop, exposed to natural sunlight radiation and temperature changes without shading and excluding precipitation (for details of the drying process see Schreckinger et al, 2021). Migrated and control sediments were sampled from the crest (≤1 cm) of migrating bedform and stationary sediment patches, respectively, at base flow in October 2018 (Supplementary Figure S2C).…”

The Impact of Drought Stress on Soil Microbial Community, Enzyme Activities and Plants

“…In the case of 'RGT-Reform' wheat cultivar, drought negatively affected xylosidase and glucosidase activities in the Chernozem soil but promoted glucosidase activities in Luvisol [22]. Drought impact on sediment revealed de-crease in esterase (0.5%/day) [61], β-glucosidase (>50%) [62], leucine aminopeptidase [63], phosphatase (>50%) [64], and phenol oxidase (PO) [63] activities. In the case of Mediterranean evergreen oak forests, a reduction of 10 and 21% of soil moisture in plots (by water runoff) decreased urease activity by 10-67% and 42-60%, protease activity by 15-66% and 35-45%, and β-glucosidase activity by 10-80% and 35-83% depending on the annual period (spring and autumn) and soil depth (0-15 and 15-30 cm).…”

Greenhouse gas dynamics in river networks fragmented by drying and damming

“…Moreover, the relatively stronger land‐water connectivity in headwaters compared to the mainstem can supply terrestrially derived C inputs to stream under lotic conditions (Hotchkiss et al, 2015), and it may be an important source of C during drying events (Gómez‐Gener et al, 2020). The shading effects of riparian cover in headwaters also can buffer against the negative impacts of sediment desiccation on decomposer communities and associated GHG production (Schreckinger et al, 2021). However, the lower sediment temperature near the headwaters and coarser sediment texture may conversely limit CO 2 fluxes.…”