Microbial biomass and activities in a Japanese paddy soil with differences in atmospheric CO_2 enrichment, soil/water warming and rice cultivars

摘要

Paddy surface and subsurface soil samples were collected from former Rice-FACE (free-air CO_2 enrichment) sites with elevated soil/water temperature treatment in successive rice crop season to investigate effect of CO_2 and temperature on microbial biomass, enzyme activities, and methanogenic and methanotrophic activities in a paddy soil. The FACE experiment was conducted in the field, with two CO_2 levels, ambient and ambient + 200 mu L/L (FACE), located in Shizukuishi, Iwate, Japan until 2004. A warming treatment of soil/water temperature of 2 degree from transplanting until harvest (May-September 2006) was set up with water-proof heater in flooded water in the field. Soil microbial biomass C were significantly larger in surface layer than those in subsurface soil, but effect of previous CO_2 treatment and warming treatment on microbial biomass were both not significant. Dehydrogenase activity and dissolved organic carbon (DOC) had no significant difference between elevated and ambient temperature, though significantly higher in surface soil than sub-surface soil. Methane (CH4) production (methanogenic) activity was increased by elevated temperature, but no effect on CH4 oxidation (methanotrophic) activity. These results indicated that elevatedtemperature may affect soil microbial processes in different ways.