Predicting Anaerobic Microsites in Soils

<p>Anaerobic microsites in soils are critical features in the Earth system as they are prime locations for generating powerful greenhouse gases. These processes occur in hot spots and hot moments and are therefore difficult to capture in mean-field approaches. Typically, they are captured as empirical functions of soil moisture.</p> <p>We present a mechanistic upscaling of microsites from single soil particles to the soil column, by considering existing formulations that link the processes of solute diffusion, pore sizes and particle size distributions, and water retention. The upscaling allows to predict probability density functions of volume and surface area of anaerobic microsites, which can then be integrated to the scale of a laboratory soil sample or a field site. Our goal was to make these predictions based on variables typically measured in soils and are routine diagnostic or prognostic variables in Earth system model. While the detailed expressions can only be solved numerically, we found closed-form solutions with little loss of accuracy.  Our result have the necessary hooks for direct implementation of anaerobic microbial carbon processing, methane production and nitrification-denitrification processes in Earth System models. A first application yields two soil moisture-CO2 efflux hypotheses that could potentially be tested and which set this upscaling apart from empirical formulations 1) the degree of temperature sensitivity and dependence of carbon concentration in anaerobicity and 2) different CO2 response to soil moisture if measured in laboratory jars vs. measured in the field.</p> <p> </p>

Anaerobic bacterial degradation of protein and lipid macromolecules in subarctic marine sediment

Microorganisms in marine sediments play major roles in marine biogeochemical cycles by mineralizing substantial quantities of organic matter from decaying cells. Proteins and lipids are abundant components of necromass, yet the taxonomic identities of microorganisms that actively degrade them remain poorly resolved. Here, we revealed identities, trophic interactions, and genomic features of bacteria that degraded 13C-labeled proteins and lipids in cold anoxic microcosms containing sulfidic subarctic marine sediment. Supplemented proteins and lipids were rapidly fermented to various volatile fatty acids within 5 days. DNA-stable isotope probing (SIP) suggested Psychrilyobacter atlanticus was an important primary degrader of proteins, and Psychromonas members were important primary degraders of both proteins and lipids. Closely related Psychromonas populations, as represented by distinct 16S rRNA gene variants, differentially utilized either proteins or lipids. DNA-SIP also showed 13C-labeling of various Deltaproteobacteria within 10 days, indicating trophic transfer of carbon to putative sulfate-reducers. Metagenome-assembled genomes revealed the primary hydrolyzers encoded secreted peptidases or lipases, and enzymes for catabolism of protein or lipid degradation products. Psychromonas species are prevalent in diverse marine sediments, suggesting they are important players in organic carbon processing in situ. Together, this study provides new insights into the identities, functions, and genomes of bacteria that actively degrade abundant necromass macromolecules in the seafloor.