Growth of soil microorganisms is often described as carbon limited, and adding labile carbon to soil often results in a transient and large increase in respiration. In contrast, soil microbial biomass changes little, suggesting that growth and respiration are decoupled in response to a carbon pulse. Alternatively, measuring bulk responses of the entire community (total respiration and biomass) could mask ecologically important variation among taxa in response to the added carbon. Here, we assessed taxon-specific variation in cellular growth (measured as DNA synthesis) and metabolic activity (measured as rRNA synthesis) following glucose addition to soil using quantitative stable isotope probing with H2 18 O. We found that glucose addition altered rates of DNA and rRNA synthesis, but the effects were strongly taxon-specific: glucose stimulated growth and rRNA transcription for some taxa, and suppressed these for others. These contrasting taxon-specific responses could explain the small and transient changes in total soil microbial biomass. Responses to glucose were not well predicted by a priori assignments of taxa into copiotrophic or oligotrophic categories. Across all taxa, rates of DNA and rRNA synthesis changed in parallel, indicating that growth and activity were coupled, and the degree of coupling was unaffected by glucose addition. This pattern argues against the idea that labile carbon addition causes a large reduction in metabolic growth efficiency; rather, the large pulse of respiration observed with labile substrate addition is more likely to be the result of rapid turnover of microbial biomass, possibly due to trophic interactions. Our results support a strong connection between rRNA synthesis and bacterial growth, and indicate that taxon-specific responses among soil bacteria can buffer responses at the scale of the whole community.

中文翻译：

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葡萄糖在微生物生长和活动中引发强烈的分类单元特异性反应：来自 DNA 和 RNA qSIP 的见解

土壤微生物的生长通常被描述为碳限制，向土壤中添加不稳定的碳通常会导致呼吸作用的短暂和大量增加。相比之下，土壤微生物生物量几乎没有变化，这表明生长和呼吸对碳脉冲的响应是分离的。或者，测量整个群落的整体响应（总呼吸和生物量）可以掩盖分类群之间对添加的碳的生态重要变化。在这里，我们使用 H2 18 O 定量稳定同位素探测，评估了向土壤中添加葡萄糖后细胞生长（以 DNA 合成衡量）和代谢活动（以 rRNA 合成衡量）的分类群特异性变化。我们发现，葡萄糖添加改变了 DNA 的速率和 rRNA 合成，但其影响具有很强的分类群特异性：葡萄糖刺激了某些分类群的生长和 rRNA 转录，并抑制了其他分类群的生长和 rRNA 转录。这些对比鲜明的分类群特异性反应可以解释总土壤微生物生物量的微小和瞬时变化。通过先验地将分类群划分为营养型或寡营养型类别，并不能很好地预测对葡萄糖的反应。在所有分类群中，DNA 和 rRNA 的合成速率同时发生变化，表明生长和活性是耦合的，耦合程度不受葡萄糖添加的影响。这种模式与不稳定的碳添加会导致代谢生长效率大幅降低的观点相反。相反，添加不稳定底物时观察到的大呼吸脉冲更有可能是微生物生物量快速周转的结果，可能是由于营养相互作用。