EFFECT OF VARIOUS TREATMENTS ON CONTENTS OF ADENINE-NUCLEOTIDES AND RNA OF MEDITERRANEAN SOILS

Changes in adenine nucleotides (ATP, ADP and AMP) were investigated in soils subjected to various treatments and compared with bacterial and fungal counts. An organic and a clay soil stored for 3 yr at room temperature showed low ATP concentrations (0.36 and 0.26 nmol g-1, respectively) which markedly increased after moistening both soils; this indicates that the prolonged storage did not eliminate the capacity of ATP synthesis by these soils; in the organic soil bacteria and fungi were unaffected by moistening while only bacterial counts were increased in the clay soil. By moistening soil with NaN3 solution the ATP increase was annulled in the organic soil and only reduced in the clay soil. Air-drying a sandy clay-loam soil resulted in a 40% drop in ATP while microbial counts were unaffected; rewetting the air-dried soil to 50% of the water holding capacity (WHC) did not increase ATP. Decrease in the ATP content was more marked when moistened or rewetted soils rather than fresh or air-dried soils were fumigated; the fumigation of soils moistened with the NaN3 solution generally decreased the ATP concentration. Sodium azide generally decreased recoveries of ATP, ADP and AMP especially in the organic soil; the effect of the inhibitor on enzymatic conversion of AMP to ADP and of ADP to ATP was also investigated in the soil extracts. Adenylate energy charge (AEC) values of moist field samples were 0.65, 0.70 and 0.80 for clay, sandy-clay loam and organic soils, respectively. Air-drying moist soils caused a marked drop in ATP and RNA and an increase in ADP, AMP and total adenine nucleotides. The AEC value of CHCl3 fumigated fresh moist soil were very low ranging from 0.06 to 0.1 thus indicating a large prevalance of dead cells even if the bacterial numbers by plate count were moderately affected.