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6年生のスギ林縁木の樹冠について,乾重あたりの葉の窒素含量を樹冠の深さと葉 齢別に調べた.当年葉の窒素含量は相対光強度と正の相関にあり,樹冠が深くなるほど低下した.しかし,1年葉以上では樹冠が深くなっても低下せず,さらに葉齢が進んでも低下しなかった.このことからスギ樹冠において,1年葉以上の窒素含量は一 定値として仮定出来ることが確かめられた.1年葉以上の窒素含量が変化しない原因には着生部位の光強...度が低いことと,窒素が新しい葉に転流していることの2点が考えられた.特に転流に関しては,1年葉以上の窒素含量は当年葉の構築に必要な窒素含量より低い値を示したことから,新しい葉への窒素の供給源として役立っていると考えられた.
The distribution of nitrogen with varying leaf age was measured in the crown of a six-year-old sugi(Cryptomeria japonica D. Don) tree at the edge of a stand. The nitrogen content (expressed on a weight basis) of current leaves was positively correlated with light intensity and decreased with increasing depth from the top of the crown. However, though the depth of the crown increased, the nitrogen content of leaves one or more years old did not decrease. Furthermore, the content did not decrease as leaf age increased. This demonstrated that nitrogen content of old leaves could be held constant in modeling canopy photosynthesis of sugi trees. Two reasons are suggested to explain why the nitrogen content of old leaves did not change. One is that the light intensity of old leaves was low. The other is that the nitrogen of old leaves was translocated to the new leaves. Since the nitrogen content of old leaves was lower than the value required for producing new leaves, nitrogen in old leaves may play an important role in supplying nitrogen to new leaves.続きを見る
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