Faculty of Agriculture, Yamagata University, Wakabamachi 1-26, Tsuruoka 997-8555, Japan.
Rapid Commun Mass Spectrom. 2011 Nov 15;25(21):3298-302. doi: 10.1002/rcm.5227.
Temporal changes in the acquisition of nitrogen (N) are recorded in tree-rings together with unique N isotopic values. Some debate continues regarding the importance of wood pre-treatment in isotope analysis and, thus, this study focuses on the removal of labile components to determine the intrinsic nature of N in tree-rings. The total concentration and stable isotopic value of N in annual tree-rings were determined for two cores from Japanese black pine (Pinus thunbergii) from areas colonized by black cormorant (Phalacrocorax carbo). One core sample was also collected from a control site, without cormorants. Sharp increases in tree-ring δ(15)N values associated with migration of the cormorant population indicate positive incorporation of N from soils, whereas a less pronounced trend was observed for ring samples for periods without or substantially less migration, and for those obtained from the control site. All labile N components were removed by repeated extraction with toluene/ethanol (1:1) solution. Radial translocation of labile N is limited in tree-rings from Japanese black pine, providing intrinsic records on N acquisition. The difference in N isotopic values (up to 7.0‰) following pre-treatment was statistically significant for trees affected by the avian colony, whereas the pre-treatment of the control samples did not influence N values. The implication is that in agreement with previous studies pre-treatment is not necessary when trees are exposed to natural N concentrations in the soil but the removal of enriched δ(15)N labile components is necessary when woody plants are exposed to unusually high inputs of N into soils. However, the temporal trend in tree-ring δ(15)N series of the avian N affected trees did not change. Thus, if the priority is not the value but the trend then pre-treatment is not necessary.
树木年轮中记录了氮（N）的获取时间变化，同时还记录了独特的 N 同位素值。关于木材预处理在同位素分析中的重要性，仍存在一些争议，因此本研究侧重于去除易变成分，以确定树木年轮中 N 的固有性质。从被黑鸬鹚（Phalacrocorax carbo）殖民的日本黑松（Pinus thunbergii）的两个芯样中，确定了年度树木年轮中 N 的总浓度和稳定同位素值。还从没有鸬鹚的对照点采集了一个芯样。与鸬鹚种群迁移相关的树木年轮 δ(15)N 值的急剧增加表明，土壤中的 N 得到了积极的吸收，而在没有或迁移量明显较少的时期，以及在对照点获得的环样本中，观察到的趋势不太明显。通过用甲苯/乙醇（1:1）溶液反复提取，去除了所有易变 N 成分。日本黑松树木年轮中的易变 N 径向迁移受到限制，为 N 吸收提供了内在记录。受鸟类群体影响的树木在预处理后 N 同位素值（高达 7.0‰）的差异具有统计学意义，而对照样品的预处理对 N 值没有影响。这意味着与之前的研究一致，当树木暴露在土壤中的自然 N 浓度下时，预处理不是必需的，但当木本植物暴露在土壤中异常高的 N 输入下时，必须去除富含 δ(15)N 的易变成分。然而，受鸟类 N 影响的树木年轮 δ(15)N 系列的时间趋势并没有改变。因此，如果重点不是价值，而是趋势，那么预处理不是必需的。
