Abstract. Microbial respiration, growth, and turnover are driving processes in the formation and decomposition of soil organic matter. In contrast to respiration and growth, microbial turnover and death currently lack distinct methods to be determined. Here we propose a new approach to determine microbial death rates and to improve measurements of microbial growth. By combining sequential DNA extraction to distinguish between intracellular and extracellular DNA and 18O incorporation into DNA, we were able to measure microbial death rates. We first evaluated methods to determine and extract intracellular and extracellular DNA separately. We then tested the method by subjecting soil from a temperate agricultural field and a deciduous beech forest to either 20, 30, or 45 °C for 24 h. Our results show that while mass-specific respiration and gross growth either increased with temperature or remained stable, microbial death rates strongly increased at 45 °C and caused a decrease in microbial biomass and thus in microbial net growth. We further found that also extracellular DNA pools decreased at 45 °C compared to lower temperatures, further indicating the enhanced uptake and recycling of extracellular DNA along with increased respiration, growth, and death rates. Additional experiments including soils from more and different ecosystems as well as testing the effects of factors other than temperature on microbial death are certainly necessary to better understand the role of microbial death in soil C cycling. We are nevertheless confident that this new approach to determine microbial death rates and dynamics of intracellular and extracellular DNA separately will help to improve concepts and models of C dynamics in soils in the future.

中文翻译：

---

通过考虑土壤中的细胞外 DNA 改进微生物生长、死亡和周转的测量


摘要。微生物的呼吸、生长和周转是土壤有机质形成和分解过程的驱动过程。与呼吸和生长相反，微生物更新和死亡目前缺乏明确的方法来确定。在这里，我们提出了一种新方法来确定微生物死亡率并改进微生物生长的测量。通过结合顺序 DNA 提取来区分细胞内和细胞外 DNA 以及 18O 掺入 DNA，我们能够测量微生物死亡率。我们首先评估了分别测定和提取细胞内和细胞外 DNA 的方法。然后，我们测试了该方法，将温带农田和落叶山毛榉林的土壤置于 20、30 或 45°C 的温度下 24 小时。我们的结果表明，虽然质量比呼吸和总生长随温度增加或保持稳定，但微生物死亡率在 45°C 时急剧增加，导致微生物生物量减少，从而导致微生物净生长减少。我们进一步发现，与较低温度相比，细胞外 DNA 池在 45°C 时也有所减少，进一步表明细胞外 DNA 的吸收和循环增强，同时呼吸、生长和死亡率增加。为了更好地了解微生物死亡在土壤碳循环中的作用，当然有必要进行更多实验，包括来自更多不同生态系统的土壤，以及测试温度以外的因素对微生物死亡的影响。尽管如此，我们仍然相信，这种分别确定微生物死亡率以及细胞内和细胞外 DNA 动态的新方法将有助于改善未来土壤中 C 动态的概念和模型。