Abstract Accurate estimation of microbial carbon use efficiency (CUE) in soil is challenged by a high degree of genetic and environmental variability. Different methods vary in their estimates of soil microbial CUE giving the room to select the optimal method for a specific research task, while integrating different methods could improve our understanding of processes controlling CUE variability. Aiming to estimate CUE during plant residue decomposition in different soils, we applied the conventional C-balance method, single C-cycling enzymatic stoichiometry (SCE-STM) and newly proposed “multi”-C-cycling enzymatic stoichiometry (MCE-STM) methods. The STM approach derives CUE from elemental ratios of microbial biomass, substrate, and activities of C and nutrient (e.g. N) acquiring exoenzymes. The extended MCE-STM is a modification of the SCE-STM method, where we used the sum of three C-cycling enzymatic activities (β-glucosidase (BGL), β-D-cellobiohydrolase (BCL), β-xylosidase (BXL)) as proxy for CUE calculation, instead of using a single C-acquiring enzyme (BGL). We hypothesized that MCE-STM provides a more reliable estimation of microbial CUE in soils amended with complex plant residues than the SCE-STM or the C balance approach. The comparison of methods was done in a laboratory incubation experiment, using two soils differing mainly in acidity level mixed with two specimen of plant residues differing in lignin (L) and polyphenol (PP) content. We anticipated a higher microbial CUE in less acidic (pH 5.1) soil amended with higher quality (lower (L + PP)/N) ratio)) plant residues than in more acidic (pH 4.3) soils amended with medium quality (higher (L + PP)/N ratio) plant residues, due to less energy investment in microbial metabolism in the former case. Microbial CUE estimations were completed at 7, 15, 30, 45 and 60 days. Lower CUE values (0.09–0.18) were recorded by MCE-STM as compare to those (0.24–0.47) obtained by C-balance and SCE-STM methods. Irrespective of applied CUE estimation methods, higher CUE was recorded in less acidic (pH 5.1) soil amended with residues of higher quality than the other three combinations. Microorganisms invested more energy to support growth in low pH soil in order to tolerate soil acidity, which, in turn, suppressed N-acquiring enzymatic activity and further decreased CUE. The modification of the MCE-STM method for CUE determination proposed in this work was capable to quantify the combined effect of soil pH and plant residue quality on efficiency of microbial metabolism. It, therefore, can be considered as viable alternative to the original stoichiometric modeling approach (SCE-STM).

中文翻译：

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植物残体分解过程中的微生物碳利用效率：整合多酶化学计量和碳平衡方法

摘要 土壤中微生物碳利用效率 (CUE) 的准确估计受到高度遗传和环境变异的挑战。不同的方法对土壤微生物 CUE 的估计各不相同，这为特定研究任务提供了选择最佳方法的空间，而整合不同的方法可以提高我们对控制 CUE 变异性过程的理解。为了估计不同土壤中植物残体分解过程中的 CUE，我们应用了传统的 C-平衡方法、单 C-循环酶化学计量 (SCE-STM) 和新提出的“多”-C-循环酶化学计量 (MCE-STM) 方法. STM 方法从微生物生物量、底物和 C 和营养物（例如 N）获取外酶的活性的元素比率得出提示。扩展的 MCE-STM 是对 SCE-STM 方法的修改，我们使用了三种 C-循环酶活性（β-葡萄糖苷酶 (BGL)、β-D-纤维二糖水解酶 (BCL)、β-木糖苷酶 (BXL)）的总和) 作为 CUE 计算的代理，而不是使用单个 C 获取酶 (BGL)。我们假设，与 SCE-STM 或 C 平衡方法相比，MCE-STM 对用复杂植物残留物修正的土壤中的微生物 CUE 提供了更可靠的估计。方法的比较是在实验室孵化实验中进行的，使用两种主要酸度不同的土壤与两种木质素 (L) 和多酚 (PP) 含量不同的植物残留物样本混合。我们预计在用更高质量（较低（L + PP）/N 比））植物残留物修正的酸性较低（pH 5.1）土壤中，微生物 CUE 比在酸性较强（pH 4）中更高。3) 用中等质量（较高（L + PP）/N 比）植物残留物改良的土壤，因为在前一种情况下微生物代谢的能量投入较少。微生物 CUE 估计在 7、15、30、45 和 60 天完成。与通过 C-balance 和 SCE-STM 方法获得的值 (0.24-0.47) 相比，MCE-STM 记录的 CUE 值 (0.09-0.18) 较低。不管应用的 CUE 估计方法如何，在用比其他三种组合更高质量的残留物修正的酸性较低（pH 5.1）土壤中记录到更高的 CUE。微生物投入更多的能量来支持低 pH 值土壤的生长，以耐受土壤酸度，这反过来又抑制了获得氮的酶活性并进一步降低了 CUE。在这项工作中提出的用于 CUE 测定的 MCE-STM 方法的修改能够量化土壤 pH 值和植物残留质量对微生物代谢效率的综合影响。因此，它可以被视为原始化学计量建模方法 (SCE-STM) 的可行替代方案。