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Full 15N tracer accounting to revisit major assumptions of15N isotope pool dilution approaches for gross nitrogenmineralization

机译：完整的15N示踪剂会计可重新考虑以下主要假设15N同位素池稀释总氮的方法矿化

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The 15N isotope pool dilution (IPD) technique is the only available method for measuring gross ammonium (NH4+) production and consumption rates. Rapid consumption of the added 15N-NH4+ tracer is commonly observed, but the processes responsible for this consumption are not well understood. The primary objectives of this study were to determine the relative roles of biotic and abiotic processes in 15N-NH4+ sconsumption and to investigate the validity of one of the main assumptions of IPD experiments, i.e., that no reflux of the consumed 15N tracer occurs during the course of the experiments. We added a 15N-NH4+ tracer to live and sterile (autoclaved) soil using mineral topsoil from a beech forest and a grassland in Austria that differed in NH4+ concentrations and NH4+ consumption kinetics. We quantified both biotic tracer consumption (i.e. changes in the concentrations and 15N enrichments of NH4+, dissolved organic N (DON), NO3− and the microbial N pool) and abiotictracer consumption (i.e., fixation by clay and/or humic substances). We achievedfull recovery of the 15N tracer in both soils over the course of the48 h incubation. For the forest soil, we found no rapid consumption of the15N tracer, and the majority of tracer (78%) remained unconsumedat the end of the incubation period. In contrast, the grassland soil showedrapid 15N-NH4+ consumption immediately aftertracer addition, which was largely due to both abiotic fixation (24%) and bioticprocesses, largely uptake by soil microbes (10%) and nitrification (13%). Wefound no evidence for reflux of 15N-NH4+ overthe 48 h incubation period in either soil. Our study therefore shows that15N tracer reflux during IPD experiments is negligible forincubation times of up to 48 h, even when rapid NH4+consumption occurs. Such experiments are thus robust to the assumption thatimmobilized labeled N is not re–mobilized during the experimental periodand does not impact calculations of gross N mineralization.
机译： 15 N同位素池稀释（IPD）技术是唯一可测量总铵（NH4 + ）生产率和消耗率的方法。通常观察到快速消耗掉添加的 15 N-NH4 + 示踪剂，但是造成这种消耗的过程并不清楚。这项研究的主要目的是确定生物和非生物过程在 15 N-NH4 + 消费中的相对作用，并调查以下主要假设之一的有效性。 IPD实验，即消耗的 15 N示踪剂在实验过程中没有回流。我们添加了 15 N-NH4 + 示踪剂，使用来自奥地利山毛榉森林和草原的矿物表层土（不同于NH4 ）的生物和无菌（高压灭菌）土壤+ 浓度和NH4 + 消耗动力学。我们量化了两种生物示踪剂的消耗量（即，NH4 + ，溶解性有机氮（DON），NO3 -的浓度和 15 N富集的变化和微生物氮库）和非生物示踪剂的消耗（即用粘土和/或腐殖质固定）。我们实现了整个过程中两种土壤中 15 N示踪剂的完全回收孵育48小时。对于森林土壤，我们发现没有快速消耗 15 N示踪剂，大多数示踪剂（78％）仍未消耗在潜伏期结束时。相反，草原土壤显示食用后立即快速消耗 15 N-NH4 + 示踪剂的添加，主要是由于非生物固定（24％）和生物过程中，大部分被土壤微生物（10％）和硝化作用（13％）吸收。我们没有发现 15 N-NH4 + 回流的证据在任何一种土壤中孵育48小时。因此，我们的研究表明IPD实验中 15 N示踪剂反流对于即使快速NH4 + 孵育时间也可长达48小时发生消费。因此，这样的实验对于以下假设是稳健的：在实验期间不重新固定化标记的N不会影响总氮矿化的计算。

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