Control of the Nitrogen Isotope Composition of the Fungal Biomass: Evidence of Microbial Nitrogen Use Efficiency
Control of the Nitrogen Isotope Composition of the Fungal Biomass: Evidence of Microbial Nitrogen Use Efficiency
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DOI：
10.1264/jsme2.me18082
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发表时间：
2018-12
影响因子：
2.2
通讯作者：
K. Shinoda;M. Yano;M. Yoh;Makoto Yoshida;Akiko Makabe;Yohei Yamagata;B. Houlton;K. Koba
中科院分区：
文献类型：
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作者：
K. Shinoda;M. Yano;M. Yoh;Makoto Yoshida;Akiko Makabe;Yohei Yamagata;B. Houlton;K. Koba
土壤微生物生物量在氮矿化过程中的15 N/14 N变化可能影响不同生态系统土壤有机质的15 N/14 N。然而，这种机制的直接实验测试尚未进行。为了评估微生物氮矿化对天然氮同位素组成的潜在控制，我们在5种不同C：N比（5，10，30，50和100）的培养基中培养真菌（Aspergilluscaureus）4 d，并跟踪实验过程中微生物生物量、NH 4+和溶解性有机氮（DON：甘氨酸）中δ 15 N的变化。高速率的NH 4+从A.在低C：N培养基中，微生物生物量中δ 15 N的增加（即，C/N<30）。相比之下，NH 4+在较高C/N处理中被强烈保留，只有少量（即，<1 ‰），微生物生物量中δ 15 N变化明显。微生物生物量中δ 15 N的差异归因于低C/N基质中低δ 15 N NH 4+的损失，而不是高C/N基质。微生物氮素利用效率（NUE）与Δ 15 N（δ 15 N-生物量-δ 15 N-甘氨酸）呈负线性相关。这些结果表明，在氮素相对充足、微生物氮素利用率较低的环境中，土壤有机质δ 15 N的垂直分布特征可能与其同位素效应有关。
Changes in 15N/14N in the soil microbial biomass during nitrogen (N) mineralization have been hypothesized to influence 15N/14N in soil organic matter among ecosystem sites. However, a direct experimental test of this mechanism has not yet been performed. To evaluate the potential control of microbial N mineralization on the natural N isotope composition, we cultured fungi (Aspergillus oryzae) in five types of media of varying C:N ratios of 5, 10, 30, 50, and 100 for 4 d, and tracked changes in δ15N in the microbial biomass, NH4+, and dissolved organic N (DON: glycine) over the course of the experiment. High rates of NH4+ excretion from A. oryzae were accompanied by an increase in δ15N in the microbial biomass in low C:N media (i.e., C/N<30). In contrast, NH4+ was strongly retained in higher C/N treatments with only minor (i.e., <1 ‰) changes being detected in δ15N in the microbial biomass. Differences in δ15N in the microbial biomass were attributed to the loss of low-δ15N NH4+ in low, but not high C/N substrates. We also detected a negative linear correlation between microbial nitrogen use efficiency (NUE) and Δ15N (δ15N-biomass–δ15N-glycine). These results suggest an isotope effect during NH4+ excretion in relatively N-repleted environments in which microbial NUE is low, which may explain the vertical patterns of organic matter δ15N in soil profiles.