森林立地学会誌 森林立地45(2),2003,81〜87
Jpn.J.For.Environment
45(2), 81-87 2003
落葉広葉樹天然林のヒノキおよびスギによる人工林化が
土壌微生物相および有機炭素の無機化特性に及ぼす影響
市川貴大＊＊・山口倫之＊＊＊,＊＊＊＊・高橋輝昌＊＊＊・浅野義人＊＊
＊＊千葉大学大学院自然科学研究科・＊＊＊千葉大学園芸学部・＊＊＊＊国際協力事業団（現勤務先）
本研究目的は，ヒノキおよびスギ人工林化による土壌の全炭素（C）量の変化の原因を明らかにすることにある。調査地は落葉広葉樹天然林伐採後に人工造林されたヒノキおよびスギ林（針葉樹林）と，天然更新した広葉樹林が同一斜面上に成立した森林である。針葉樹林の斜面上部にはヒノキが（ヒノキ林），斜面下部にはスギが（スギ林）それぞれ植栽されている。本研究では，斜面位置ごとにC動態を広葉樹林と針葉樹林の間で比較した。土壌深0-30cmにおける全C量は斜面上部のヒノキ林では広葉樹林の約0.6倍，斜面下部のスギ林では広葉樹林とほぼ同じであった。土壌中のバイオマスC量，土壌呼吸速度，微生物の加水分解酵素活性，セルロース分解能，窒素無機化量は斜面上部のヒノキ林では広葉樹林の0.3〜0.5倍，斜面下部のスギ林では広葉樹林の0.6〜1.3倍であった。これらの傾向は概ね土壌の全C量を反映していた。落葉のC無機化速度は斜面上部ではヒノキ落葉で広葉樹落葉の約1.2倍，斜面下部ではスギ落葉で広葉樹落葉の約0.8倍であった。このことから，ヒノキ落葉は斜面上部の広葉樹落葉より無機化されやすく，土壌中に有機物を蓄積されにくいこと，スギ落葉は斜面下部の広葉樹落葉より無機化されにくく，土壌中に有機物を蓄積されやすいことが考えられた。
Takahiro
Ichikawa, Tomoyuki Yamaguchi, Terumasa Takahashi and Yoshito Asano : Effects of
the conversion of the forest management type from natural deciduous
broad-leaved forests to artificial Japanese cypress (Chamaecyparis obtusa)
and Japanese cedar (Cryptomeria japonica) forests on soil microbial
flora and mineralization characteristics of organic carbon
The
purpose of this study is to clarify the reason for changes in the soil carbon
contents depending on the conversion of the forest management type from natural
deciduous broad-leaved forests (broad-leaved forests) to artificial Japanese
cypress and Japanese cedar forests (coniferous forests). In the coniferous
forests, Japanese cypress (Chamaecyparis obtusa) was planted on the
upper slop and Japanese cedar (Cryptomeria japonica) was planted on the
lower slope. In this study, comparisons of the results were made between the
broad-leaved forest and coniferous forest in each slope position. The soil
carbon content in the cypress forest was about 0.6 times lower than that of the
broad-leaved forest on the upper slope. On the other hand, the soil carbon
content in the cedar forest was almost the same to that of the broad-leaved
forest on the lower slope. The amounts of soil microbial biomass C and soil
respiration rates, metabolic activity of the soil microorganisms, cellulose
decomposition rates and the amounts of nitrogen mineralization of the cypress
forest was 0.3-0.5 times lower than that of the broad-leaved forest. The
amounts of soil microbial biomass C and soil respiration rates, metabolic
activity of the soil microorganisms, cellulose decomposition rates and the
amounts of nitrogen mineralization of the cedar forest was 0.6-1.3 times than
that of broad-leaved forest. These tendencies reflected the soil carbon
contents. The carbon mineralization rate of the cypress litter was 1.2 times
higher than that of the broad-leaved litter on the upper slope. The carbon
mineralization rate of cedar litter was 0.8 times lower than that of the
broad-leaved litter on the lower slope. This suggested that the cypress litter
had been easily mineralized and had been difficult to accumulate relative to
the litter in the broad-leaved forest on the upper slope, while the cedar
litter had been mineralized with difficulty which provided a rapid accumulation
relative to the litter in the broad-leaved forest on the lower slope.