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Isotopic composition and concentration of total nitrogen and nitrate in xylem sap under near steady-state hydroponics.
Plant, Cell & Environment ( IF 6.0 ) Pub Date : 2020-05-28 , DOI: 10.1111/pce.13809
Yi Hu 1 , Robert D Guy 1
Affiliation  

After root uptake, nitrate is effluxed back to the medium, assimilated locally, or translocated to shoots. Rooted black cottonwood (Populus trichocarpa) scions were supplied with a NO3‐based (0.5 mM) nutrient medium of known isotopic composition (δ15N), and xylem sap was collected by pressure bombing. To establish a sampling protocol, sap was collected from lower and upper stem sections at 0.1–0.2 MPa above the balancing pressure, and after increasing the pressure by a further 0.5 MPa. Xylem sap from upper stem sections was partially diluted at higher pressure. Further analysis was restricted to sap obtained from intact shoots at low pressure. Total‐, NO3‐N and, by difference, organic‐N concentrations ranged from 6.1–11.0, 1.2–2.4, and 4.6–9.4 mM, while discrimination relative to the nutrient medium was −6.3 to 0.5‰, −23.3 to −11.5‰ and − 1.3 to 4.9‰, respectively. There was diurnal variation in δ15N of total‐ and organic‐N, but not NO3. The difference in δ15N between xylem NO3 and organic‐N suggests that discrimination by nitrate reductase is near 25.1 ± 1.6‰. When this value was used in an isotope mass balance model, the predicted xylem sap NO3‐N to total‐N ratio closely matched direct measurement.

中文翻译:

接近稳态水培条件下木质部汁液中同位素组成及总氮和硝酸盐浓度

根吸收后,硝酸盐外排回培养基,被本地吸收,或转移到芽上。将生根的黑三角叶(毛果杨)接穗与NO分别供给3 -为基础的(0.5毫摩尔)已知同位素组成的营养培养基(δ 15 N),和木质部汁液通过压力轰炸收集。为了建立采样方案,在高于平衡压力0.1–0.2 MPa的压力下,从上部和下部茎部收集汁液,然后再增加0.5 MPa的压力。来自上部茎部分的木质部汁液在较高压力下被部分稀释。进一步的分析仅限于从完整芽在低压下获得的汁液。Total-,NO 3 -‐N和有机N的差异范围为6.1–11.0、1.2–2.4和4.6–9.4 mM,而相对于营养培养基的辨别力为-6.3至0.5‰,-23.3至-11.5‰和-1.3分别为4.9‰。有在δ日变化15的total-和有机-N N,而不是NO 3 - 。在δ之差15木质部NO之间的N个3 -和有机-N表明由硝酸还原酶歧视是接近25.1±1.6‰。在同位素质量平衡模型中使用此值时,预测的木质部汁液NO 3 -- N与总N的比率与直接测量值非常匹配。
更新日期:2020-05-28
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