Extremely thermophilic endospores germinate and metabolise organic carbon in sediments heated to above 80°C

Endospores of thermophilic bacteria are widespread in cold seabed environments where they remain dormant during initial burial in accumulating sediments. The temperature increase during sedimentation can be simulated in experimental heating of sediments, resulting in the temperature-dependent activation of different endospore populations from the microbial seed bank. Here we investigated the response of endospore populations to heating at extreme high temperature (80– 99°C). Metabolites for germination and organic matter degradation (dipicolinic acid and organic acids) revealed both endospore germination and subsequent metabolism at ≥80°C. Endospore-forming Firmicutes with the genomic potential for organic carbon and nitrogen transformation were recovered by genome-resolved metagenomics. Genomes from Symbiobacteriales, Thermosediminibacteriales, Moorellales and Calditerricolales encode multiple mechanisms for high temperature degradation of sedimentary organic carbon and features of necromass that accumulate during sediment burial including saccharides, amino and nucleic acids. The results provide insight into the metabolism of novel carbon cycling microorganisms activated at high temperature, and suggest that extremely thermophilic Firmicutes dispersed in the ocean are poised to germinate in response to sediment heating during burial and transform a wide range of organic substrates.

A re-evaluation of wetland carbon sink concepts and measurements: A diagenetic solution down sediments

Aquatic canopy ecosystems ability to mitigate greenhouse gases (GHG) is currently based on the rate of sedimentary organic carbon accumulation (CA) and the protection of vulnerable stocks from remineralisation. However, remineralisation of allochthonous inputs constrains CA as sequestration, assessments neglect remineralisation over climatic scales, and often fail to account for recalcitrant material. The article clarifies the meaning of stock and sequestration as mitigation services through their net ecosystem production (NEP) and addresses the concerns through a series of hypothetical evolving ecosystems. A diagenetic solution is proposed that accounts for continuous remineralisation of CA and the remineralised fraction of labile allochthonous inputs to estimate the NEP. The solution was applied and tested for a seagrass and mangrove ecosystem. Uncorrected and corrected average CA was greater than the cal. NEP values by a factor of two for the seagrass and 30 for the mangrove. Nevertheless, the NEP values fell within reported ranges i.e., 27.6 g C m-2 yr-1 (mangrove) and 7.2 g C m-2 yr-1 (seagrass). The overestimate was largely maintained after including vulnerable stocks in the total carbon accreditation calculus. However, with the inclusion of CA, the total average carbon mitigation rates converged to 1 124 (seagrass) and 1 783 g C m-2 yr-1 (mangroves), when argued, in some circumstances, as a vulnerable stock concept after hindcasting to their original time of annual deposition. Mitigation concepts and measurements require re-evaluation and will assure that carbon credits are not overvalued, which would otherwise permit GHG emissions above the capacity of the ecosystem.