© 2007 Heron Publishing—Victoria, Canada
Seasonal and spatial variations in leaf nitrogen content and resorption in a Quercus serrata canopy
Chiharu Migita (1), Yukihiro Chiba (2, 3) and Takeshi Tange (1)
1. Graduate School of Agricultural and Life Sciences, the University of Tokyo, Tokyo 113-8657, Japan / 2. Corresponding author (chiro@ffpri.affrc.go.jp) / 3. Department of Plant Ecology, Forestry and Forest Products Research Institute, Ibaraki 305-8687, Japan / Received December 12, 2005; accepted April 9, 2006; published online October 2, 2006
Summary
To elucidate the relationships between spatiotemporal changes in leaf nitrogen (N) content and canopy dynamics, changes in
leaf N and distribution in the canopy of a 26-year-old deciduous oak (Quercus serrata Thunb. ex. Murray) stand were monitored throughout the developmental sequence from leaf expansion to senescence, by estimating
the leaf mass and N concentrations of all the canopy layers. Seasonal changes were observed in leaf N concentration per unit
leaf dry mass (Nm), which peaked after bud burst, declined for two weeks shortly thereafter, and then remained constant for the rest of the
growing season for each canopy layer. Leaf N concentration per unit leaf area (Na) was higher in the upper layer than in the lower layer throughout the growing season, and was closely correlated with relative
irradiance (RI) in the summer when the air temperature was moderately high. The N concentrations of all leaf layers started
to decrease in November, and reached their lowest values in late November, whereas LMA scarcely changed throughout the season.
The lowest N concentrations did not differ significantly among the canopy layers. Seasonal changes in the relationship between
Na and RI were detected, indicating that Na is optimized temporally as well as spatially. Nitrogen resorption efficiency was highest in the upper canopy layers where
larger amounts of N were invested. Based on the estimates of leaf mass and leaf N concentrations of the canopy layers, total
leaf N concentration of the whole canopy was estimated to be 84.1 kg ha–1 in the summer, and 37.3 kg ha–1 in late November. Therefore, 46.8 kg ha–1 of leaf N in the canopy (about 56% of the total N) was resorbed just before leaf abscission.
Keywords:
canopy structure, leaf phenology, leaf senescence, LMA, relative irradiance.
