Isotopic composition and concentration of total nitrogen and nitrate in xylem sap under near steady-state hydroponics.
Plant Cell Environ
; 43(9): 2112-2123, 2020 09.
Article
em En
| MEDLINE
| ID: mdl-32463123
ABSTRACT
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 (δ15 N), 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 δ15 N of total- and organic-N, but not NO3- . The difference in δ15 N 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.
Palavras-chave
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Populus
/
Xilema
/
Nitratos
/
Nitrogênio
Tipo de estudo:
Prognostic_studies
Idioma:
En
Revista:
Plant Cell Environ
Assunto da revista:
BOTANICA
Ano de publicação:
2020
Tipo de documento:
Article
País de afiliação:
Canadá