森林立地学会誌　森林立地47(1), 2005, 29～37

Jpn.J.For.Environment 47(1), 29-37 2005

カラマツ人工林化にともなう土壌化学性の変化

―隣接する広葉樹林土壌との比較―

杉本真由美^＊＊・川崎圭造^＊＊＊

^＊＊京都大学大学院農学研究科・^＊＊＊信州大学農学部

　カラマツ人工林化による土壌の化学性の変化を隣接する広葉樹林土壌と比較した。A₀層の元素含有量の多少は，カラマツ林と広葉樹林で一定の傾向は認められなかった。カラマツ落葉の分解率（k）は0.19，広葉樹葉の分解率は0.29であり，カラマツ林では広葉樹林に比べて堆積有機物の分解に伴う鉱質土層への元素還元速度が遅いことが示された。鉱質土壌表層（0～5cm）の全P，全Cおよび全N濃度は，A₀層の元素含有量や濃度に関係なく，カラマツ林の方が広葉樹林に比べて低く，それぞれ0.73倍，0.66倍および0.64倍であった。鉱質土層の交換性Mg，交換性Kおよび交換性Na濃度も同様に，カラマツ林の方が広葉樹林よりも低く，それぞれ0.36倍，0.34倍および0.28倍であった。カラマツ人工林化によって，堆積有機物の分解に伴う鉱質土壌への元素還元量が減少することにより，鉱質土壌表層の全P，C，N，交換性Mｇ，KおよびNa濃度は減少すると考えられた。しかし，交換性Ca濃度は，他の塩基類とは異なり，鉱質土壌表層では両林に差がなく，下層ではカラマツ林の方が広葉樹林に比べて高く，1.9倍であった。鉱質土壌中のNO₃-N濃度はカラマツ林の方が広葉樹林に比べて高く，1.4～2.4倍であった。カラマツ人工林化にともなう土壌中へのNO₃-Nの集積は交換性塩基類の流亡を促す可能性が考えられた。

　Mayumi Sugimoto, Keizou Kawasaki: Changes in soil chemical properties by the conversion of natural deciduous broad-leaved forest into larch (Larix kaempferi) forest

Natural broad-leaved forest and artificial larch (Larix kaempferi) forests (40-yr-old) were compared in the amount of litter layer and its contents of C, N, P, K, Na, Ca, and Mg, rate of litter decomposition, and some chemical properties of mineral soil horizons. There were no differences in average concentrations of total C, N and P of the litter layer between the two forest types. Average concentrations of total K, Na, Ca and Mg of the litter layer were lower in the larch forest than in the broad-leaved forest. However, there were no consistent differences in the amounts of those elements in litter layer between two forest types. The decomposition rates (Olson’s k) were 0.19 and 0.29 at the larch forest and the board-leaved forest, respectively, and suggested the nutrient return to the mineral soil through litter decomposition may much smaller in the former than the latter. The concentrations of total C, N, P, exchangeable K, Na and Mg in the surface mineral soil (0-5cm depth) were 0.66, 0.64, 0.73, 0.34, 0.28 and 0.36 times lower in the larch forest than in the broad-leaved forest, respectively. It was presumed that the nutrients status in the surface mineral soil, especially in exchangeable K, Na and Mg concentrations declined due to the decreased nutrients return from litter layer with the forest conversion into the larch forest. However, the concentrations of exchangeable Ca in the lower soil layers were 1.9 times higher in the larch forest than in the broad-leaved forest, though it did not differ in the upper soil layers between them. The NO₃-N contents in mineral soils were 1.4-2.4 times higher in the larch forest than in the natural broad-leaved forest. Those findings suggested the conversion of broad-leaved forests into artificial larch forest might bring about increased NO₃-N flux in a litter-mineral soils-system, and accelerate leaching loss of basic cations from soil.

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