森林と農耕地土壌における微生物バイオマス炭素におよぼす土壌の攪拌,温度および含水比の影響

抄録

Throughout the year, the microbial biomass carbon(μg g^-1 dry soil)at a depth of 5-10cm in a forest or an arable soil classified as Andept was almost constant at 730 or 180, respectively.The biomass carbon of a forest or an arable soil classified as Ochrept was 1, 500 or 440, respectively.To examine the reasons for the lower size of biomass carbon of the arable soil compared to that of the forest soil, we studied the effect of soil agitation, temperature or moisture on the microbial biomass carbon of Andept samples incubated in a laboratory.Soil agitation for half a minute with a frequency of twice a week did not change the microbial biomass carbon of the forest or the arable soil during an incubation period of 3 months.On the other hand, the temperatures above 30ºC or the moisture levels below 35% significantly reduced the biomass carbon of the forest soil after a 2-week-incubation.However, periodic incubation at 40ºC for 4 hours and 25ºC for 20 hours daily, keeping soil moisture at 60%, did not reduce the biomass carbon of the forest soil after a 2-week-incubation.The moisture levels below 35% were observed in the arable soil at a depth of 0-3cm for a few weeks in the field, and the reduced biomass carbon of the air-dried forest soil did not recover after the soil was re-wetted.Therefore, severe desiccation seems to be one of the reasons for the lower size of microbial biomass carbon in the arable soil.