Benthic microorganisms play a significant role in the remineralization of sedimentary organic matter (OM). In order to constrain the growth rate, turnover and carbon metabolism of microbial communities in anoxic sandy sediments, we quantified the rate of inorganic carbon (IC) assimilation and of lipid production via a recently developed dual isotope-labelling assay that can differentiate autotrophic vs. heterotrophic production in a 22 cm sediment core from the Janssand tidal flat (Wadden Sea, Germany). Despite an extremely low concentration of total organic carbon (TOC) in the majority of samples (< 0.3%), the concentration of total fatty acids (TFAs) was in the range 4.5 to 28.4 μg/mg TOC, suggestive of a high contribution of fresh microbial and algal biomass to the TOC pool. This was corroborated by a production rate of microbial FAs, which ranged from 0.3 to 4.7 μg TFAs/g_dw/yr (where dw = dry wt) and the mean turnover time of microbial FAs was 6 ± 5 yr. The enhanced production rate of iso- and anteiso-branched FAs was consistent with the presence of an active population of sulfate reducing Deltaproteobacteria. The assimilation rate of inorganic carbon (IC) into bacterial lipids was relatively low (0.16 ± 0.07 μg C/g_dw/yr) in OM-lean sandy sediments (i.e. upper 17 cm), such that the IC assimilation to lipid production ratio values was typically < 0.3, indicating that heterotrophic bacteria were dominant and dark IC fixation played a minor role at the study site. The measured rates of FA production converted to anaerobic heterotrophic C demand of 0.4-1.8 µg C/g_dw/d, assuming a bacterial growth efficiency of 10%. Such high biomass proportion, production rate and C demand suggested that dissolved OM must play a vital role in sustaining the active heterotrophic microbial populations in these sandy sediments.

底栖微生物在沉积有机物（OM）的再矿化中起着重要作用。为了限制缺氧沙质沉积物中微生物群落的生长速率，周转率和碳代谢，我们通过最近开发的双同位素标记测定法（可区分自养型和非养分型）定量了无机碳（IC）同化和脂质产生的速率。来自Janssand潮滩（德国沃登海）22厘米沉积岩心中的异养生产。尽管大多数样品中的总有机碳（TOC）浓度极低（<0.3％），但总脂肪酸（TFA）的浓度范围为4.5至28.4μg/ mg TOC，这表明新鲜的微生物和藻类生物量进入TOC库。微生物FA的产生率证实了这一点，_dw / yr（其中dw =干重），微生物FA的平均周转时间为6±5年。异分支和前异分支FA的生产率提高与硫酸盐还原型Deltaproteobacteria活性种群的存在一致。OM稀砂质沉积物中无机碳（IC）对细菌脂质的同化率较低（0.16±0.07μgC / g _dw / yr）（即较高的17 cm），因此IC与脂质生产比的同化值通常小于0.3，表明异养细菌占主导地位，深色IC固定在研究地点的作用不大。实测FA转化率转化为厌氧异养C需求量0.4-1.8 µg C / g _dw/ d，假设细菌生长效率为10％。如此高的生物量比例，生产率和碳需求表明，溶解的OM必须在维持这些沙质沉积物中的活性异养微生物种群中发挥至关重要的作用。