Off-site impacts of agricultural composting: role of terrestrially derived organic matter in structuring aquatic microbial communities and their metabolic potential

Haynes, K. M., Preston, M. D., McLaughlin, J. W., Webster, K. and Basiliko, N. 2015. Dissimilar bacterial and fungal decomposer communities across rich to poor fen peatlands exhibit functional redundancy. Can. J. Soil Sci. 95: 219–230. Climatic and environmental changes can lead to shifts in the dominant vegetation communities present in northern peatland ecosystems, including from Sphagnum- to vascular-dominated systems. Such shifts in vegetation result in changes to the chemical quality of carbon substrates for soil microbial decomposers, with leaves and roots deposited in the peat surface and subsurface that potentially decompose faster. This study characterized the bacterial and fungal communities present along a nutrient gradient ranging from rich to poor fen peatlands and assessed the metabolic potential of these communities to mineralize a variety of organic matter substrates of varying chemical complexity using substrate-induced respiration (SIR) assays. Distinct microbial communities existed between rich, intermediate and poor fens, but SIR in each of the three sites exhibited the same pattern of carbon mineralization, providing support for the concept of functional redundancy, at least under standardized in vitro conditions. Preferential mineralization of simple organic substrates in the rich fen and complex compounds in the poor fen was not observed. Similarly, no preference was given to “native” organic matter extracts derived from each fen, with microbial communities opting for the most bioavailable substrate. This study suggests that soil bacteria and fungi might be able to respond relatively rapidly to shifts in vegetation communities and subsequent changes in the quality of carbon substrate additions to peatlands associated with environmental and climatic change.

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Ooids forming in situ within microbial mats (Kiritimati atoll, central Pacific)

PalZ ◽

10.1007/s12542-021-00591-6 ◽

2021 ◽

Author(s):

Pablo Suarez-Gonzalez ◽

Joachim Reitner

Keyword(s):

Organic Matter ◽

Microbial Communities ◽

Microbial Mats ◽

Formation Processes ◽

Central Pacific ◽

Environmental Processes ◽

Definition Of ◽

First Time

AbstractOoids (subspherical particles with a laminated cortex growing around a nucleus) are ubiquitous in the geological record since the Archean and have been widely studied for more than two centuries. However, various questions about them remain open, particularly about the role of microbial communities and organic matter in their formation and development. Although ooids typically occur rolling around in agitated waters, here, we describe for the first time aragonite ooids forming statically within microbial mats from hypersaline ponds of Kiritimati (Kiribati, central Pacific). Subspherical particles had been previously observed in these mats and classified as spherulites, but these particles grow around autochthonous micritic nuclei, and many of them have laminated cortices, with alternating radial fibrous laminae and micritic laminae. Thus, they are compatible with the definition of the term ‘ooid’ and are in fact very similar to many modern and fossil examples. Kiritimati ooids are more abundant and developed in some ponds and in some particular layers of the microbial mats, which leads to the discussion and interpretation of their formation processes as product of mat evolution, through a combination of organic and environmental factors. Radial fibrous laminae are formed during periods of increased supersaturation, either by metabolic or environmental processes. Micritic laminae are formed in closer association with the mat exopolymer (EPS) matrix, probably during periods of lower supersaturation and/or stronger EPS degradation. Therefore, this study represents a step forward in the understanding of ooid development as influenced by microbial communities, providing a useful analogue for explaining similar fossil ooids.

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Metabolic profiling suggests two sources of organic matter shape microbial activity, but not community composition, in New Zealand fjords

10.1101/745273 ◽

2019 ◽

Author(s):

Sven P. Tobias-Hünefeldt ◽

Stephen R. Wing ◽

Federico Baltar ◽

Sergio E. Morales

Keyword(s):

Organic Matter ◽

Microbial Communities ◽

Microbial Activity ◽

Community Composition ◽

Sediment Resuspension ◽

Metabolic Diversity ◽

New Production ◽

Metabolic Potential ◽

Microbial Carbon ◽

And Function

AbstractFjords are semi-enclosed marine systems with unique physical conditions that influence microbial communities structure. Pronounced organic matter and physical condition gradients within fjords provide a natural laboratory for the study of changes in microbial phylogeny and metabolic potential in response to environmental conditions (e.g. depth). In the open ocean new production from photosynthesis supplies organic matter to deeper aphotic layers, sustaining microbial activity. We measured the metabolic diversity and activity of microbial communities in fjords to determine patterns in metabolic potential across and within fjords, and whether these patterns could be explained by community composition modifications. We demonstrated that metabolic potential and activity are shaped by similar parameters as total (prokaryotic and eukaryotic) microbial communities. However, we identified increases in metabolic diversity and potential (but not in community composition) at near bottom (aphotic) sites consistent with the influence of sediments in deeper waters. Thus, while composition and function of the microbial community in the upper water column was likely shaped by marine snow and sinking POM generated by new production, deeper sites were strongly influenced by sediment resuspension of benthic organic matter generated from this or other sources (terrestrial, chemoautotrophic, microbial carbon loop), uncoupling the community composition and function dynamics.

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