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B-6.3.3 Quantitative estimation of cellulolytic enzyme system in soil and its relation to global climate warming

[Contact Person]

Tomoyuki Hakamada. Associate Division Director for Research, Division of Environmental Planning,National Institute of Agro-environmental Sciences. Kan-nondai 3-1-1, Tsukuba, Ibaraki, 305 Japan

Total Budget for FY 1996-1998:

7,546,000Yen(Fy 1998: 2,501,000yen)

Global production of cellulose by plant is calculated to be 10¹¹ ton/year and most of the cellulose is supplied to soil as plant residue. Cellulase is a key enzyme in decomposition of plant residue because it operates at first step in the process that cellulose-C is mineralized to carbon dioxide and released to atmosphere. This study is aimed to predict the impact of global climate warming on cellulolytic activity in soil. For this purpose, we investigate the cellulase activity in soils sampled from various agricultural sites in the north latitude 25^治 to 45^治 in Japan. Especially, we investigate properties concerning temperature, such as optimum temperature and Q₁₀ of cellulase activities in soils. Twenty-six soil samples were taken from following sites: Ishigaki(lat. 24.2^治, annual temp. 23.8C^治 ), Tokunoshima(lat. 27.4^治, ann. temp.21.2C^治 ), Kagoshima(lat. 31.3^治, ann. temp.17.3C^治 ) Chikugo(lat. 33.1^治, ann. temp.16.0C^治 ), Sapporo(lat. 43^治, ann. temp. 8.3 C^治 ) and Hamatonbetsu(lat. 45^治 ,ann. temp.5.3C^治 ). p-Nitrophenyl-β -cellobioside was used for assay of cellulase activity in soil. Optimum temperature of cellulase activity in soil ranged from 55.6 to 67.0^。C. Significant correlation was observed between the optimum temperature of the cellulase activity and annual temperature at sampling site (r = 0.602^**). Q₁₀ of cellulase activities between 20 and 30^。C ranged from 1.6 to 2.8. Correlation between Q₁₀ and annual temperature was not significant. However, the lower in assay temperature of the enzyme activity, the Q₁₀ value became larger. Following β-glucosidic substrate other than p-nitrophenyl-β-cellobioside was also hydrolyzed by soil extracts; p-nitrophenyl-β-cellotrioside, carboxymethyl cellulose and microcrystallin cellulose. Hydrolysis of p-nitrophenyl-β-cellotrioside by soil extracts was competitively inhibited by microcrystallin cellulose but not by carboxymethyl cellulose. Hydrolytic activity of the soil extracts to insoluble substrate was lower than that to soluble substrtate.

[Key Words]

Cellulolytic enzymes. Soil Enzymes, Agricultural soil, Optimum temperature. Q₁₀