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Cycling dynamics of NH4+ and amino acid nitrogen in soils of a deciduous boreal forest ecosystem

机译：落叶北方森林生态系统土壤中NH4 +和氨基酸氮的循环动力学

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Conventional studies of nitrogen (N) cycling in forest ecosystems have focused on inorganic N uptake as the primary source of N for plant metabolism. More recently, however, alternative sources of N for plant nutrition, such as free amino acids, have gained attention, particularly in nutrient-limited systems. Using a multiple stable isotope (C-13 and N-15) design, that allowed us to simultaneously assess root uptake of ammonium (NH4+) and glycine, we compared the cycling dynamics of NH4+ and amino acid N within the soils of several interior Alaskan floodplain balsam poplar stands. Our design included multiple sampling periods extending from 45 min to 14 days, which permitted us to study interpool transfers of our carbon (C) and N isotopes over time. Microbial biomass N was the largest sink of both N-15-ammonium and glycine. Percent recovery of N-15 for this pool was an order of magnitude larger than fine-root N-15 uptake for most sampling periods. Although recovery of N-15 in fine-root biomass was small, amino acid N and NH4+ were assimilated at approximately the same rate irrespective of sampling period, and total recovery was still increasing 2 weeks after application. Recovery of N-15 in bulk soil samples did not vary significantly over time for either treatment. However, bulk soil C-13 declined steadily during the experiment, measuring less than 30% recovery of added label after 14 days. We suspect that the majority of C-13 lost from our soils was respired. Soil microorganisms strongly outcompeted plants in the short term for both NH4+ and amino acid N. However, amino acid N appears to cycle through soil N pools at approximately the same rate as inorganic N forms. The similarity in uptake patterns for inorganic and organic N suggests that these stands are meeting part of their N requirements directly from amino acids.
机译：森林生态系统中氮（N）循环的常规研究集中于吸收无机氮作为植物代谢氮的主要来源。然而，最近，植物营养的替代氮源（例如游离氨基酸）已引起关注，特别是在营养有限的系统中。使用多重稳定同位素（C-13和N-15）设计，使我们能够同时评估铵盐（NH4 +）和甘氨酸的根吸收，我们比较了几个阿拉斯加内部土壤中NH4 +和氨基酸N的循环动力学洪泛区苦瓜杨树站立。我们的设计包括从45分钟到14天的多个采样周期，这使我们能够研究碳（C）和N同位素随时间的池间转移。微生物生物量氮是N-15铵和甘氨酸的最大吸收者。在大多数采样期间，该库中N-15的回收率比细根N-15吸收大一个数量级。尽管细根生物量中N-15的回收率很小，但无论采样时间长短，氨基酸N和NH4 +的吸收率都大致相同，施用后2周总回收率仍在增加。对于这两种处理，散装土壤样品中N-15的回收率均未随时间显着变化。但是，在实验过程中，散装土壤C-13呈稳定下降趋势，在14天后测得添加标签的回收率不足30％。我们怀疑从土壤中流失的大部分C-13被呼吸了。在短期内，土壤微生物在NH4 +和氨基酸N方面的竞争能力都强于植物。但是，氨基酸N似乎以与无机氮形式大致相同的速率循环通过土壤N库。无机和有机氮吸收模式的相似性表明，这些林分满足了直接来自氨基酸的部分氮需求。

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