Abstract

Isotopic composition of nitrogen in soil microbial biomass (δ¹⁵N_micr) is connected with the transformation of nitrogen compounds and with the balance of carbon and nitrogen availability for microorganisms. We have studied the dependence of δ¹⁵N_micr on nitrogen isotopic composition in the substrate (δ¹⁵N of total and extractable nitrogen), as well as the dependence of δ¹⁵N_micr and ¹⁵N-enrichment of microbial biomass (Δ¹⁵N_micr = δ¹⁵N_micr – δ¹⁵N_substr) on nitrogen availability parameters (the C/N ratio in soil, the N-mineralization activity, the content of extractable nitrogen, and the nitrogen use efficiency) in soils of four alpine ecosystems in the North Caucasus and four tundra ecosystems in the Khibiny Mountains. It has been shown that δ¹⁵N_miсr varies from –0.2 to +8.4‰ and may be characterized by both ¹⁵N-enrichment and depletion (negative Δ¹⁵N_miсr values) relative to the total and extractable soil nitrogen. As a rule, Δ¹⁵N_micr is 1.5–3.1‰ relative to ¹⁵N_total and 0.6–4.8‰ relative to ¹⁵N_extr. However, under the most N-deficiency conditions in soils of mountain tundra lichen and shrub heaths, N_micr does not accumulate an increased amount of ¹⁵N. We have not revealed a close correlation of δ¹⁵N_micr and Δ¹⁵N_micr with the C/N ratio. The accumulation of ¹⁵N in microbial biomass is much stronger related to N-mineralization (positively) and the nitrogen use efficiency (negatively). This testifies to the important role of microbial nitrogen dissimilation in controlling the isotopic composition of soil microbial biomass nitrogen.

中文翻译：

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高山和苔原生态系统中土壤微生物生物量的 15N 自然丰度

摘要

土壤微生物生物量中氮的同位素组成 (δ ¹⁵ N _micr ) 与氮化合物的转化以及微生物的碳和氮可用性平衡有关。我们研究了 δ ¹⁵ N _micr对基质中氮同位素组成的依赖性（总氮和可提取氮的δ ¹⁵ N），以及微生物生物量的 δ ¹⁵ N _micr和¹⁵ N 富集的依赖性（Δ ¹⁵ N _micr = δ ¹⁵ N _micr – δ ¹⁵ N _substr) 北高加索四个高山生态系统和希比尼山脉四个苔原生态系统土壤中氮的有效性参数（土壤中的碳氮比、氮矿化活性、可提取氮含量和氮利用效率） . 已经表明，δ ¹⁵ N_微量从 –0.2 到 +8.4‰ 变化，其特征可能是¹⁵ N 富集和消耗（负 Δ ¹⁵ N_微量值）相对于土壤总氮和可提取氮。通常，Δ ¹⁵ N _micr相对于¹⁵ N_总量为1.5–3.1‰，相对于¹⁵ N_提取量为 0.6–4.8‰. 然而，在山地苔原地衣和灌木荒地土壤中最缺氮的条件下，N _micr并没有积累¹⁵ N的增加量。我们没有揭示 δ ¹⁵ N _micr和 Δ ¹⁵ N _micr与信噪比。微生物生物量中¹⁵ N的积累与 N 矿化（正）和氮利用效率（负）的相关性更强。这证明了微生物氮异化在控制土壤微生物生物量氮同位素组成方面的重要作用。