Frutschi, M. | Search bioRxiv

bioRxiv2024

Impact of redox fluctuations on the spatial distribution of the microbial community in a forest soil: A lysimeter experiment

Climate change is expected to affect precipitation intensity and soil temperature and indirectly impact the release of leached dissolved organic carbon (LDOC) from leaf litter during the early stages of its decomposition, which could affect the health and function of forest soil ecosystem. Here, we experimentally investigate the spatially-explicit impact of LDOC on the forest soil microbiome and the associated biogeochemical processes. Homogenized soil columns were subjected to realistic artificial precipitation for 3 months with the initial level of LDOC adjusted by the number of times the leaf litter was flushed in preparation for the experiment. Hydrological and geochemical parameters (redox potential, pH, dissolved oxygen, soil moisture, matric potential, chemical speciation) were measured continuously as a function of time and depth. The same initial microbial community developed into distinct communities under different LDOC and above and below the water table. The LDOC from leaf litter increased the availability of carbon (C) and nitrogen (N) in porewater four-fold and two-fold respectively in the first two weeks. This resulted in the expansion of the anoxic zone above the water table and a decrease in the soil microbial metabolic potential for cellulolysis and N2 fixation in unsaturated soil along with an increase of soil microbial metabolic potential for fermentation at all depths. Finally, increased LDOC decreased the stability, phylogenetic diversity, and complexity of the soil microbiome, limiting its functional diversity. Thus, management of leaf litter should receive more attention due to its indirect role in the impact of climate change on the soil microbiome. HighlightsO_LIDecreased microbiome diversity and stability due to enhanced leaf litter leaching C_LIO_LIExpansion of the anoxic zone into the unsaturated zone due to increased organic carbon supply C_LIO_LIDecreased soil microbiome metabolic potential for cellulolysis and N2 fixation in unsaturated soil C_LIO_LIDepth-dependent response of microbial community to increased organic carbon availability C_LIO_LIImplications for soil response to climate change C_LI

microbiology↗

bioRxiv2021

Active anaerobic methane oxidation and sulfur disproportionation in the deep terrestrial subsurface

Microbial life is widespread in the terrestrial subsurface and present down to several kilometers depth, but the energy sources that fuel metabolism in deep oligotrophic and anoxic environments remain unclear. In the deep crystalline bedrock of the Fennoscandian Shield at Olkiluoto, Finland, opposing gradients of abiotic methane and ancient seawater-derived sulfate create a terrestrial sulfate-methane transition zone (SMTZ). We used chemical and isotopic data coupled to genome-resolved metaproteogenomics to demonstrate active life and, for the first time, provide direct evidence of active anaerobic oxidation of methane (AOM) in a deep terrestrial bedrock. Proteins from Methanoperedens (formerly ANME-2d) are readily identifiable despite the low abundance ([≤]1%) of this genus and confirm the occurrence of AOM. This finding is supported by 13C-depleted dissolved inorganic carbon. Proteins from Desulfocapsaceae and Desulfurivibrionaceae, in addition to 34S-enriched sulfate, suggest that these organisms use inorganic sulfur compounds as both electron donor and acceptor. Zerovalent sulfur in the groundwater may derive from abiotic rock interactions, or from a non-obligate syntrophy with Methanoperedens, potentially linking methane and sulfur cycles in Olkiluoto groundwater. Finally, putative episymbionts from the candidate phyla radiation (CPR) and DPANN archaea represented a significant diversity in the groundwater (26/84 genomes) with roles in sulfur and carbon cycling. Our results highlight AOM and sulfur disproportionation as active metabolisms and show that methane and sulfur fuel microbial activity in the deep terrestrial subsurface. Significance StatementThe deep terrestrial subsurface remains an environment in which there is limited understanding of the extant microbial metabolisms, despite its reported large contribution to the overall biomass on Earth. It is much less well studied than deep marine sediments. We show that microorganisms in the subsurface are active, and that methane and sulfur provide fuel in the oligotrophic and anoxic subsurface. We also uncover taxonomically and metabolically diverse ultra-small organisms that interact with larger host cells through surface attachment (episymbiosis). Methane and sulfur are commonly reported in terrestrial crystalline bedrock environments worldwide and the latter cover a significant proportion of the Earths surface. Thus, methane- and sulfur-dependent microbial metabolisms have the potential to be widespread in the terrestrial deep biosphere.

microbiology↗