Fig. 4

Maximum potential rates of biological assimilation and dissimilation (oxidation or reduction) of select one-carbon compounds by planktonic microbial communities in subsurface well waters collected from the Samail Ophiolite. Maximum potential rates of biological formate (HCOO⁻) oxidation to carbon dioxide (CO₂) and assimilation of HCOO⁻ to biomass (a), bicarbonate (HCO₃⁻) reduction to methane (CH₄) and HCO₃⁻ assimilation to biomass (b), carbon monoxide (CO) oxidation to CO₂ and CO assimilation to biomass (c), and the ratio of the rate of substrate dissimilation (reduction or oxidation) to assimilation (to biomass) (d). The pH of each well is displayed in parentheses below the well name. Rates of substrate transformation were determined via microcosm assays using radiolabeled carbon tracers. Rates of substrate transformation in abiological controls were subtracted from biological assays to determine rates that are attributable to biology. Statistical significance of differences between biological assays and abiological controls were assessed via Student’s t-test assuming unequal variance for each condition (*p < 0.05, **p < 0.01). Error bars reflect the standard deviation of measurements of three replicate biological assays and three replicate abiological assays for each condition