Gross nitrogen retranslocation within a canopy of Quercus serrata saplings

• Published in: Tree physiology Vol. 32; no. 7; pp. 859 - 866
• Main Author: Ueda, Miki U
• Format: Journal Article
• Language: English
• Published: Canada 01.07.2012
• Subjects: Absorption; Analysis of Variance; Biological Transport; Biomass; Fertility; Isotope Labeling; Nitrogen - metabolism; Nitrogen Isotopes; Plant Leaves - metabolism; Plant Shoots - metabolism; Quercus - growth & development; Quercus - metabolism; Seasons
• ISSN: 0829-318X; 1758-4469
• DOI: 10.1093/treephys/tps050

Nitrogen (N) retranslocation within tree canopies has been intensively studied and assumed to function as a one-way process (e.g., from older to newer leaves). However, recent studies have found that both N output and input occur in individual leaves, suggesting that 'gross' N retranslocation exists behind 'net' N retranslocation. In the present study, the amount and direction of gross N retranslocation within a canopy of deciduous oak Quercus serrata Thunb. ex. Murray saplings were investigated. Labeling was conducted with leaves of Q. serrata saplings cultivated under conditions of low-N (LN) or high-N (HN) fertility. Subsequently, N movement within the canopy was traced. Leaves at two different positions in the canopy (top and lateral) were labeled to determine the direction of gross N retranslocation. To detect seasonal differences, the leaf-labeling experiment was conducted twice during the early and late phases of the growing season. In addition, to compare the quantitative importance of gross N retranslocation and root N uptake, the latter was determined by labeling Q. serrata roots. The N-labeling experiment revealed gross N retranslocation among leaves, i.e., from top to lateral, lateral to top and lateral to lateral positions. Gross N retranslocation was quantitatively more important than root uptake, especially for plants cultivated at LN fertility. Season also affected the amount of gross N retranslocation, and these effects differed between LN and HN fertilities. These findings suggest that N allocation within a canopy is controlled dynamically by both gross N output and input. The mechanisms controlling gross N output and input likely function as key determinants of N allocation within a tree canopy.