© 2004 Heron Publishing—Victoria, Canada
Relationships between light, leaf nitrogen and nitrogen remobilization in the crowns of mature evergreen Quercus glauca trees
Shin-Ichi Miyazawa (1, 2, 3), Arata Antonio Suzuki (1), Kosei Sone (1) and Ichiro Terashima (1)
1. Department of Biology, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan / 2. Centre for Forest Biology, Department of Biology, University of Victoria, P.O. Box 3020, Victoria, BC, V8W 3N5, Canada / 3. Corresponding author (miyazawa@uvic.ca) / Received December 15, 2003; accepted February 20, 2004; published online August 2, 2004
Summary
We estimated the amount of nitrogen (N) remobilized from 1-year-old leaves at various positions in the crowns of mature Quercus glauca Thunb. ex Murray trees and related this to the production of new shoots. Leaf N concentration on an area basis (Na) and total N (Nt = Na × lamina area of all leaves on a shoot) were related to photosynthetic photon flux (PPF) on the leaves of current-year and
1-year-old shoots. When new shoots (S02 shoots; flushed in 2002) flushed, only a portion of the leaves on the previous year’s
shoots (S01 shoots; flushed in 2001) were shed. After the S02 shoots flushed, S01 shoots were defined as 1-year-old shoots
(S01* shoots). Both Na and Nt were positively correlated with PPF for S01 shoots, but not for S01* shoots. The fraction of remobilized N (% of the maximum
Na in S01 leaves) from remaining leaves was 5–35%, with the fraction size being positively correlated with the number of S02
shoots on an S01* shoot (new shoot number). However, the mean fraction of remobilized N from fallen leaves was 45% and was
unrelated to new shoot number. The total amount of N remobilized from both fallen and remaining leaves was 1–20 mg per S01*
shoot. Total remobilized N was positively correlated with new shoot number. There was a statistically significant positive
relationship between the light-saturated net photosynthetic rate on a leaf area basis (Amax) and Na for both S01* and S02 leaves. However, when we compared leaves with similar Na, Amax of S01* leaves was only half that of S02 leaves, indicating that 1-year-old leaves had lower instantaneous N-use efficiency
(Amax per unit Na) than current-year leaves. Ratios of chlorophyll a:b and Rubisco:chlorophyll were lower in S01* leaves than in S02 leaves,
indicating that 1-year-old leaves were acclimatized to lower light environments. Thus, in Q. glauca, the N allocation theory (i.e., that N is distributed according to local PPF) applied only to the current-year shoots. Although
the amount of foliar N in 1-year-old shoots was not strongly affected by the PPF on 1-year-old leaves, it was affected by
interactions with current-year shoots.
Keywords:
evergreen, leaf age, light, nitrogen, remobilization, shoot.
