Biology subjects

LaBrie, R.

Publications and source records attributed to LaBrie, R..

3 recordsLinked to original sources

bioRxiv2025

Small- and large-scale patches shape benthic microbial community structure and function in streams at the subcontinental scale

Streams and rivers process dissolved and particulate matter as water moves along the land-to-ocean continuum, making important contributions to global biogeochemical cycles. Yet, predicting stream and river microbial metabolism associated with biogeochemical transformations at broad spatial scales remains challenging. Here, we used data from the National Ecological Observatory Network program to investigate whether ecological relationships among microbial community structure and function and environmental conditions observed at small scales hold at the subcontinental scale. We found that microbial communities were best explained by site-specific conditions. However, when field replicates were averaged, stream physico-chemical characteristics such as pH and temperature emerged as driving factors. This indicates that water quality acted as an environmental filter on microbial communities at the subcontinental scale, but was masked by small-scale patches that created high spatial heterogeneity. Our findings underscore the importance of considering multiple spatial scales to fully understand benthic microbial communities role in stream biogeochemistry. SCIENTIFIC SIGNIFICANCE STATEMENTMicrobial communities in streams process materials as water flows toward the ocean. As microbial communities are influenced by environmental conditions, it remains challenging to predict stream microbial metabolism at large spatial scales. In this study, we used the National Ecological Observatory Network (NEON) public database to investigate the drivers of microbial community structure and functions in stream sediments across the USA. This unique dataset revealed high variability in microbial communities among streams that were best explained by local conditions, then by water quality and streambed habitat type. However, stream physico-chemical characteristics emerged as strong predictors of microbial communities when field replicates were averaged and considered as single, large microbial communities. These findings indicate multiple spatial scales must be considered to fully understand benthic microbial communities.

ecology↗

bioRxiv2025

Testing the priming effect in the deep ocean: are microbes too starved to consume recalcitrant organic carbon?

Deep ocean dissolved organic carbon (DOC) is one of the largest pools of reduced carbon on Earth. Many DOC compounds escape microbial degradation and persist for thousands of years in the ocean. Although many hypotheses have been proposed, the mechanisms responsible for this long-term stability remain unresolved. Heterotrophic microorganisms in the deep ocean are energetically starved and exhibit low metabolic activity. Here, we investigated whether the severe energy limitation in deep sea environments acts as a barrier to microbial degradation of DOC. We hypothesized that alleviating this energetic barrier through the addition of labile compounds (i.e., the priming effect) could stimulate microbial consumption of DOC. We conducted 62-day bottle incubations with deep seawater from the Southern Ocean that were amended with simple organic carbon, nitrogen- and/or phosphorus-containing compounds. We tracked DOC concentration, cell abundance and microbial community structure over the course of the experiment. Our results show no evidence of a priming effect regardless of the priming compound. However, priming compounds selected for distinct microbial populations with little overlap among amended bottles even when compounds were chemically similar. Pseudoalteromonas and Pseudomonas were enriched across all amended bottles, and their competition for labile substrates likely contributed to observed variations in DOC consumption. Our results reveal that the persistence of DOC is not driven by the energetic state of deep-sea microbes. In contrast, our results suggest that inputs of fresh carbon to the deep ocean are more likely to increase DOC sequestration, via the microbial carbon pump, rather than stimulate DOC consumption. IMPORTANCEThe oceans store vast amounts dissolved organic carbon (DOC) that can resist microbial degradation for thousands of years. The mechanisms that underlie the long-term stability of DOC in the ocean are still debated. Microorganisms in this environment exhibit low metabolic activity and are energetically starved. We tested whether the microbial degradation of DOC could be stimulated through the addition of labile compounds. Surprisingly, alleviating energetic constraints did not stimulate the consumption of deep ocean DOC. Additionally, our results suggest that competition among taxa is an important constraint on dissolved organic carbon consumption, with implications for ecosystem processing. Our study indicates that an increase in fresh organic carbon to the deep ocean may enhance carbon sequestration since marine microbes are known to produce recalcitrant compounds. Among other applications, this finding is of consequence for ongoing geoengineering efforts that aim to remove atmospheric carbon by increasing carbon export to the deep sea.

ecology↗

bioRxiv2022

Anoxic age as a new tool to predict biogeochemical consequences of oxygen depletion in lakes

Lake deoxygenation is of growing concern because it threatens ecosystem services delivery. Complete deoxygenation, anoxia, is projected to prolong and expand in lakes, promoting the production or release of nutrients, greenhouse gases and metals from water column and the sediments. Accumulation of these compounds cannot be easily predicted thus hindering our capacity to forecast the ecological consequences of global changes on aquatic ecosystems. Here, we used lakes Arendsee and Mendota monitoring data to develop a novel metric, anoxic age, characterizing lake hypolimnetic anoxia. Anoxic age explained, as a single predictor, 44% to 58% of the variation for ammonium, soluble reactive phosphorus and a dissolved organic matter fluorophore. Anoxic age could be modelled using only two oxygen profiles and lake bathymetry, making it an easily applicable tool to interpret and extrapolate biogeochemical data. This novel metric thus has the potential to transform widely available oxygen profiles into an ecologically meaningful variable. Scientific Significance StatementOxygen depletion in deep water layers of lakes is of growing concern as it expands due to eutrophication and climate change. Anoxia is deleterious to benthic invertebrates and fishes, enables the production of potent greenhouse gases and releases stored phosphorus from sediments, among others. However, quantitatively forecasting the consequences of anoxia remains a challenge. Here, we developed a novel metric, anoxic age, which may be derived from oxygen profiles to predict end-of-summer concentration of various water chemical parameters. We argue that all by-products of anaerobic microbial metabolism should be related to anoxic age as they are released or processed continuously during anoxia. We believe that anoxic age can be used to predict the ecological consequences of temporally and spatially growing anoxia.

ecology↗