Microbial Diversity and Function in Shallow Subsurface Sediment and Oceanic Lithosphere of the Atlantis Massif

The subsurface rock beneath the ocean is one of the largest biospheres on Earth, and microorganisms within influence global-scale nutrient cycles. This biosphere is difficult to study, in part due to the low concentrations of microorganisms that inhabit the vast volume of the marine lithosphere.

Low Light Availability Reduces the Subsurface Sediment Carbon Content in Halophila beccarii From the South China Sea

Eutrophication, dredging, agricultural and urban runoffs, and epiphyte overgrowth could reduce light availability for seagrass. This may affect “blue carbon” stocks in seagrass beds. However, little research is available on the effect of light intensities on carbon sequestration capacity in seagrass beds, especially small-bodied seagrasses. The dominant seagrass Halophila beccarii, a vulnerable species on the IUCN Red List, was cultured in different light intensities to examine the response of vegetation and sediment carbon in seagrass beds. The results showed that low light significantly reduced leaf length and above-ground biomass, while carbon content in both above-ground and below-ground tissues were not affected. Low light reduced both the above-ground biomass carbon and the total biomass carbon. Interestingly, while under saturating light conditions, the subsurface and surface carbon content was similar, under low light conditions, subsurface sediment carbon was significantly lower than the surface content. The reduction of subsurface sediment carbon might be caused by less release flux of dissolved organic carbon from roots in low light. Taken together, these results indicate that reduced light intensities, to which these meadows are exposed to, will reduce carbon sequestration capacity in seagrass beds. Measures should be taken to eliminate the input of nutrients on seagrass meadows and dredging activities to maintain the “blue carbon” storage service by enhancing light penetration into seagrass.

Dyadobacter bucti sp. nov., isolated from subsurface sediment

A Gram-reaction-negative, yellow-pigmented, rod-shaped, aerobic, non-motile, non-spore-forming bacterium, designated strain QTA69T, was isolated from a subsurface sediment sample collected at the Qiangtang basin, Qinghai–Tibetan Plateau, PR China. Cells were catalase-positive and oxidase-negative. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain QTA69T was a member of the genus Dyadobacter and was closely related to Dyadobacter sediminis , Dyadobacter ginsengisoli and Dyadobacter psychrophilus with sequence similarities from 97.90 % to 96.85 %. Strain QTA69T grew at 4–35 °C, and the optimum temperature was 25–28 °C. It grew at the pH range of 6.0–9.0 (optimum, pH 7.0–8.0) and its NaCl tolerance was 0–2.0 % (optimum, 0–1.0 %). The major cellular fatty acids were summed feature 3 (iso-C15 : 0 2-OH and C 16:1ω6c/C16 : 1ω7c), iso-C15 : 0 and C16 : 1ω5c. The major respiratory quinone was MK-7 and the major polar lipid was phosphatidylethanolamine. Genome sequencing revealed a genome size of 8.41 Mbp and a G+C content of 46.87 mol%. Based on whole genome average nucleotide identity values, phenotypic data, phylogenetic data and genotypic data, strain QTA69T represents a novel species of genus Dyadobacter , for which the name Dyadobacter bucti sp. nov is proposed. The type strain is QTA69T (=CGMCC 1.13688T=KCTC 72024T).

Macrofauna and roots reduce methane production and attenuate nutrient recycling in organic-rich fluvial sediments

<p>Organic-rich freshwater sediments display millimetric oxygen and nitrate penetration and are sources of methane to the water column and to the atmosphere via diffusion and ebullition. Radial oxygen loss by submersed aquatic plants and burrow irrigation with O<sub>2</sub> and NO<sub>3</sub><sup>-</sup> enriched water by macrofauna can significantly alter the subsurface sediment volume where respiration processes alternative to methanogenesis occur. We tested this hypothesis in perifluvial organic sediments colonized by the submerged phanerogam <em>Vallisneria spiralis</em> and the oligochaete <em>Sparganophilus tamesis</em>. Gas ebullition and diffusive fluxes were measured in microcosms maintained under controlled laboratory conditions over a period of two weeks. Four conditions were reproduced: sediments alone, sediment with oligochaetes, sediment with plants and sediment with plants and oligochaetes. Microcosms with sediments alone released the largest methane volume whereas sediments with plants and macrofauna released the lowest amount. The presence of the oligochaete had comparatively a stronger effect than that of the macrophyte. Simultaneously, the bioturbation activity of the oligochaete enhanced the production of N<sub>2</sub> and the consumption of oxygen and nitrate, suggesting increased rates of aerobic respiration and of denitrification. The presence of plants attenuated net N<sub>2</sub> losses from the benthic system likely due to the competition between assimilative and dissimilative N-related processes.</p>