Seasonal variation of soil protease activities and their relation to proteolytic bacteria and Bacillus spp in paddy field soil
1995
Watanabe, K. | Hayano, K.
Hydrolytic activities toward benzyloxycarbonyl-L-phenylalanyl-L-leucine (z-FLase) and casein (caseinase) in soil were measured during rice cultivation, before irrigation, before and after midsummer drainage, and before and after the final drainage. The activities were maintained at a high level in three paddy fields, an organic-manure field (z-FLase, 191-684 pKat g-1 dry wt soil; caseinase, 220-652 pKat g-1 dry wt soil), a chemical-fertilizer field (z-FLase, 368-472 pKat g-1 dry wt soil; caseinase, 319-773 pKat g-1 dry wt soil) and a no-fertilizer field (z-FLase, 358-702 pKat g-1 dry wt soil; caseinase, 424-758 pKat g-1 dry wt soil). The total numbers of bacteria did not correlate with soil protease activities. Numbers of proteolytic bacterial groups, counted on azocoll agar plates and with a MPN method, correlated well with the soil z-FLase activity (r = 0.625 to 0.767). Numbers of vegetative cells and total cells of Bacillus spp decreased after irrigation and continued to decrease until after the final drainage, with only a weak negative correlation between their number and soil water content (r = -0.488 and -0.555). The ratio of spores-to-total cell numbers of Bacillus spp increased after irrigation and reached a maximum after 1-2 months, when 43-100% of Bacillus cells existed as spores. The number of spores of Bacillus spp was weakly correlated with the soil caseinase activity (r = 0.459)
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