RESPONSE OF ATP CONTENT, RESPIRATION, RATE AND ENZYMES ACTIVITIES IN ARABLE AND A FOREST SOIL TO NUTRIENT ADDITIONS

Glucose (C), glucose plus NO3- (C+N) or glucose plus NO3- plus PO43- (C+N+P) were added to an arable and a forest soil at a single dose, or split into four equal doses over 4 consecutive days, and the response of several enzyme activities, ATP content and respiration rate were monitored for 11 days. beta -Glucosidase activity was reduced in the two soils during the first day by substrate addition. Thereafter, this enzyme activity varied only slightly in the arable soil with reference to the non-amended control, while it increased substantially in the beach forest when C+N and C+N+P were added, Casein-hydrolysing activity increased in the C treatment and decreased after C+N+P addition during the first 4 days in the two soils. After-ii days, protease activity was enhanced in the arable soil when C+N was applied in a split dose. Urease activity decreased during the first 4 h, particularly in the arable soil,with the addition of C+N or C+N+P, applied in a single dose, and then continuously increased. Thus, urease responded to high nutrient availability, being firstly repressed or inhibited, and stimulated afterwards. Phosphatase activity was only slightly modified in the arable soil but substantially increased in the beech forest by C+N addition. The presence of P usually decreased phosphatase activity. Arylsulphatase activity was repressed after substrate addition, which was particularly evident in the arable soil. In the beech forest topsoil, C added alone increased this enzyme activity. Significant correlations between ATP content and enzyme activity were only observed for urease in the arable system treated with C+N and in the forest when C was applied in a split dose. The effect of C, C+N and C+N+P addition varied between the arable and the forest soil according to environmental conditions and microbial ecophysiology.