森林立地学会誌 森林立地41(2),1999,59〜66
Jpn.J.For.Environment41(2),59-66
1999
Effects of carbon properties on
characteristics of nitrogen mineralization
in forest soil of Kanto region,
Japan
Hiroto Toda and Kikuo Haibara
Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509,
Japan
The parameters of N mineralization
potential (No), the N mineralization
rate constant (k) and apparent
activation energy (Ea) are normally
estimated by mathematieal analysis using a kinetics model based on results of
the in vitro incubation in forest
soil of the Kanto region, Japan. The relationships between N mineralization
parameters and chemical properties and carbon mineralization potential (Co) in forest soil were investigated.
Soil samples were taken from Japanese cedar (Cyptomeria japonica) stands (3 plots), Japanese cypress (Chamaecyparis obtusa) Stands (3 plots)
and deciduous broad-leaved stands (1 plot) in Gunma Prefecture, Japan, and from
evergreen broad-leaved stands, a matebasii (Lithocarpus
edulis) stand (1 plot) and a sudajii
(Caslanopsis cuspidata var sieboldii) stand (1 plot) in Chiba
Prefecture, Japan. Soil samples were taken at depths of 0-10cm (or 0-5cm and
5-10cm) and 10-20cm in each plot. The relationship between the C/N ratio and N
mineralization parameters was not significant in any of the soil samples.
However, in soil samples where the C/N ratio was ≧20, No
increased and Ea decreased as the C/N
ratio decreased. There was a positive correlation between Co and No the regression
line was Co/No≒20. k was the greatest and Ea was the smallest when Co was between 7 and 8% of total C (Co/C). This suggests that there is
little Co available for N
mineralization when Co/C<7-8% and
that there is sufficient Co for N
immobilization when Co/C>7-8%.
Thus, C properties are important as indicators of movements of the amount of
available N in forest soil.
戸田浩人・生原喜久雄:関東地方の森林土壌における炭素の窒素無機化特性に及ばす影響。
森林立地(巻),(59〜66),(年)。関東地方の森林土壌における窒素無機化をビン培養法で測定し反応速度論によって解析することで,可分解性窒素量(No),反応速度定数(k),見かけの活性化エネルギー(Ea)という3つの窒素無機化特性値を求めた。これらの特性値と土壌の化学性および可分解性炭素量(Co)との関係を調査した。土壌採取は,群馬県のスギ林(Cryptomeria japonica)とヒノキ林(Chamaecyparis obtusa)を3ヶ所ずつ,落葉広葉樹林を1ケ所,千葉県の常緑広葉樹林を2ケ所(マテバシイ林(Lithocarpus
edulis)とスタジイ林(Castanopsis cuspidata var. sieboldii)),それぞれ深き0〜5,5〜10cm(もしくは0〜10cm)および10〜20cmよりおこなった。全土壌試料においては,C/N比と窒素無機化特性値の間に相関性がなかった。しかし,C/N比≧20の土壌では,C/N比の小さいほど,Noが大きくEaが小さくなった。CoとNoに正の相関性があり,回帰直線はCo/C≒20となった。全炭素量に対するCoの割合(Co/C(%))が7〜8%で,kは最大,Eaは最小であった。Co/C<7〜8%では微生物による窒素無機化に有効な易分解性炭素が不足で,Co/C>7〜8%では易分解性炭素が多く炭素の有機化が生じると推察される。以上のように,森林土壌中の炭素の特性は,林木の利用可能な窒素の動態を把握する上で重要と考えられる。