Within Annual Ring and Pith-to-bark Variations of the Microfibril Angle in the S-2 Layer of Tracheid Walls in 106-year-old Plantation Trees of Japanese Larch

Observations were made of within annual ring and pith-to-bark variations of the microfibril angle of the S2 layer (MF angle) of tracheid walls in 106-year-old plantation trees of Japanese larch (Larix kaempferi Carr.). The MF angle was measured by the iodine method. The MF angle within the annual ring decreased from the beginning to the end region of earlywood, whereas in latewood there was less variation than in earlywood, regardless of cambial age. The decrease in MF angle in earlywood is gradual in rings of younger cambial age, whereas it is abrupt in rings of older cambial age, regardless of the rate of radial growth. The pith-to-bark variations of MF angle were found to be constant in earlywood. On the other hand, the MF angle of latewood decreased abruptly in the younger stage followed by a stable smaller angle in the older stage after the 15th to 30th rings. There was no significant correlation between ring width and MF angle of latewood in mature wood (after the 30th ring). 106年生の高樹齢カラマツ（Larix kaempferi Carr.）造林木5個体を対象として，仮道管二次壁中層（S2層）のセルロースミクロフィブリル傾角（以下MF傾角）をヨウ素法により測定した。MF傾角の年輪内変動は形成層齢によらず，早材では外側に向かうにつれて減少し，晩材では早材よりも変動が小さかった。早材のはじめから早晩材境界にかけてのMF傾角の減少傾向は肥大成長速度の大小に関わらず，形成層齢の増加に伴い緩やかな減少から急激な減少へと変化した。MF傾角の樹幹内半径方向変動は，晩材では形成層齢の増加に伴い急激に減少した後，緩やかな減少に変化し，30年輪以降その変動は小さくなった。早材では形成層齢の増加に伴う減少は認められなかった。30年輪以降において年輪幅と晩材MF傾角には有意な相関は認められないことから，成熟材部の晩材MF傾角は年輪幅の変動の影響を受けないといえる。Article木材学会誌. 59(3):121-127 (2013)journal articl