A pinboard by
Chloé Orland

PhD student, University of Cambridge


Linking terrestrial and aquatic ecosystems: how lake sediment microbes decompose terrestrial carbon

The boreal ecozone holds an estimated 60% of the world’s freshwater, but lakes in this region tend to be nutrient-poor and less productive, making their production reliant on carbon subsidies from riparian litterfall. The availability of these carbon subsidies for aquatic food webs, however, depends on microbial communities in lake sediment. Little is known about how the taxonomic and functional diversity of heterotrophic bacteria might influence the rate at which this terrestrial organic matter (OM) is decomposed. Drawing upon biodiversity-ecosystem functioning theory, we predicted that decomposition rates, indicative of both food web production and biogeochemical cycling, increase with the taxonomic and functional diversity of bacterial communities that add new abilities to degrade OM. We characterized both bacterial community composition and microbial functional traits in nearshore sediments from 8 catchments along a gradient of terrestrial OM inputs using next-generation sequencing (16S rRNA amplicon sequencing and shotgun metagenomics). We found that both OM quantity and taxonomic diversity, and not functional diversity, promoted OM decomposition rates. The effect of taxonomic diversity on OM decomposition was mostly attributable to differences in bacterial communities among catchments irrespective of their environmental conditions, suggesting that colonization history rather than habitat-based filtering influenced community assembly. Monthly sampling of the microbial communities present in experimental mesocoms was done in parallel in order to understand the mechanisms of this colonization process. Preliminary analyses revealed the importance of founder taxa in determining community structure, and consequently ecosystem functioning. This study highlights the role of microbial communities in facilitating the transfer of resources from terrestrial ecosystems, and improves our understanding of how catchment disturbances may affect boreal aquatic ecosystems.


A meta-analysis of changes in bacterial and archaeal communities with time.

Abstract: Ecologists have long studied the temporal dynamics of plant and animal communities with much less attention paid to the temporal dynamics exhibited by microbial communities. As a result, we do not know if overarching temporal trends exist for microbial communities or if changes in microbial communities are generally predictable with time. Using microbial time series assessed via high-throughput sequencing, we conducted a meta-analysis of temporal dynamics in microbial communities, including 76 sites representing air, aquatic, soil, brewery wastewater treatment, human- and plant-associated microbial biomes. We found that temporal variability in both within- and between-community diversity was consistent among microbial communities from similar environments. Community structure changed systematically with time in less than half of the cases, and the highest rates of change were observed within ranges of 1 day to 1 month for all communities examined. Microbial communities exhibited species-time relationships (STRs), which describe the accumulation of new taxa to a community, similar to those observed previously for plant and animal communities, suggesting that STRs are remarkably consistent across a broad range of taxa. These results highlight that a continued integration of microbial ecology into the broader field of ecology will provide new insight into the temporal patterns of microbial and 'macro'-bial communities alike.

Pub.: 12 Apr '13, Pinned: 29 Jun '17

Carbon sources supporting fish growth in a north temperate lake

Abstract: Lake consumers are supported by autochthonous organic matter produced by photosynthesis within the aquatic ecosystem and imported allochthonous material produced outside the ecosystem. To evaluate carbon sources that support fish growth, we enriched a 26 ha lake with inorganic 13C. This labeled the autochthonous primary production and allowed us to determine the extent to which invertebrates in fish diets were supported by this autochthonous carbon. Fish autochthony was defined as the proportion ranging from 0 to 1 of fish growth derived from aquatic primary production. This proportion was calculated using the weighted average of each diet taxa’s contribution to fish growth along with the autochthony of diet taxa estimated with dynamic models of δ13C time series. Age 0 bluegill (Lepomis macrochirus) and yellow perch (Perca flavescens) had the highest autochthony (0.56, 0.57, respectively) because of greater use of zooplankton that were highly dependent on phytoplankton. Older fishes (age 1 and above) of all species had similar estimates of autochthony (mean=0.47 standard deviation=0.04) derived from feeding on either benthic invertebrates or other fishes. Proportional contribution of terrestrial prey (primarily terrestrial beetles) to fish growth was highest for bluegill (0.07–0.22) and substantially lower (<0.04) for largemouth bass (Micropterus salmoides) and yellow perch. Across species and ages ~ 45% of fish growth could not be attributed to terrestrial prey items or current autochthonous primary production. This residual detrital carbon source is a mixture of allochthonous material and autochthonous material derived from primary production prior to the 13C addition. Fish growth and production in the study lake were not tightly coupled to the current season’s primary production. Nearly half of the organic carbon supporting fish growth came from prior autochthonous primary production or allochthonous sources.

Pub.: 22 Sep '08, Pinned: 29 Jun '17

Identifying the core seed bank of a complex boreal bacterial metacommunity.

Abstract: Seed banks are believed to contribute to compositional changes within and across microbial assemblages, but the application of this concept to natural communities remains challenging. Here we describe the core seed bank of a bacterial metacommunity from a boreal watershed, using the spatial distribution of bacterial operational taxonomic units (OTUs) across 223 heterogeneous terrestrial, aquatic and phyllosphere bacterial assemblages. Taxa were considered potential seeds if they transitioned from rare to abundant somewhere within the metacommunity and if they were ubiquitous and able to persist under unfavorable conditions, the latter assessed by checking their presence in three deeply sequenced samples (one soil, one river and one lake, 2.2-3 million reads per sample). We show that only a small fraction (13%) of all detected OTUs constitute a metacommunity seed bank that is shared between all terrestrial and aquatic communities, but not by phyllosphere assemblages, which seem to recruit from a different taxa pool. Our results suggest directional recruitment driven by the flow of water in the landscape, since most aquatic sequences were associated to OTUs found in a single deeply-sequenced soil sample, but only 45% of terrestrial sequences belonged to OTUs found in the two deeply-sequenced aquatic communities. Finally, we hypothesize that extreme rarity, and its interplay with water residence time and growth rates, may further constrain the size of the potential seed bank.The ISME Journal advance online publication, 6 June 2017; doi:10.1038/ismej.2017.67.

Pub.: 07 Jun '17, Pinned: 29 Jun '17