森林立地 53(1),17〜22,
2011
Jpn J For Environ 53(1), 17-22, 2011
切り捨て間伐で還元されたスギ緑葉の分解に伴う林地への窒素供給
平井敬三1,†,*・野口享太郎1,‡・山中高史2・金子真司1・高橋正通1,¶
1森林総合研究所立地環境研究領域・2森林総合研究所森林微生物研究領域
切り捨て間伐で林地に還元された枝条は，その多くが地面に触れず離れた状態で存在する点に注目し，間伐後の枝条の分解にともなう窒素動態を調べた。間伐で緑葉として林地に還元された窒素量は84 kg ha-1で，その67%が地面に接地せず空中に存在していた。緑葉を入れたリターバッグを空中と地表に設置し，分解速度と分解にともなう土壌への窒素供給量を調べたところ，分解速度は設置後１年間は処理による違いはなかったが，２年後は地表で有意に速かった。残存葉の窒素含有率は設置直後から増加したが，１年後は地表の方が空中より有意に高かった。分解初期には処理に関わらず窒素を取り込み残存葉に存在する窒素量は間伐で還元された窒素量より増加した。残存葉の窒素量の増加は空中では６ヶ月後まで，地表では１年後まで続いた。分解にともなう土壌への窒素供給の開始は地表の方が空中より遅くなった。しかし，地表では１年後〜２年後の分解速度が空中より速まるため，設置後２年間の土壌への窒素供給量は空中より地表で多く，その割合は64%であった。
キーワード：空中，地表，不動化，リターバッグ
Keizo Hirai, Kyotaro Noguchi, Takashi
Yamanaka, Shinji Kaneko and Masamichi Takahashi：Nitrogen supply from
decomposing green needle after non-commercial thinning at a sugi (Cryptomeria japonica) stand. Japanese Journal of Forest
Environment 53:17−22, 2011.
Most of litter returned by non-commercial
thinning was existed without contact onto the forest floor. We discussed
nitrogen dynamics with decomposing litter after thinning with a focus on the
site difference of litter existence in this study. The amount of nitrogen returned
by thinning was 84 kg ha−1 and 67% of them were existed in the air without
contact onto the floor. Litterbag containing green needles was installed in the
air and on the surface in forest floor, and decomposition rate and nitrogen
supply with decomposing of green needles into the soil were investigated.
Decomposition rate was not differed among treatments after one year installation
but was higher in the surface than the air in two year after. Nitrogen
concentration in the remaining green needles was increased from just after
installation in both of treatment, and was statistically higher in the surface
than in the air. After decomposition, amounts of nitrogen containing in the
remaining green needles were gained by immobilization until six month after in
the air and one year after in the surface. Nitrogen supply into the soil with
green needle decomposition started early in the air compared in the ground.
Contribution of nitrogen supply into the soil from green needles installed on
the surface during two years was 64%. Because decomposition rate of green
needles installed on the surface between one and two year after higer than
those of in the air.
Key words : air, ground,
immobilization, litterbag
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