ACID-PHOSPHATASE-ACTIVITY AND PHOSPHORUS-NUTRITION IN SCOTS PINE NEEDLES

From March to October, acid phosphatase activity and phosphorus (P) co ncentration were measured in four needle age classes of the upper and lower crowns of fertilized and unfertilized Scots pine (Pinus sylvestr is L.) trees. Negative correlations between acid phosphatase activity and P concentration were observed in current-year needles and in needl es in the upper part of the crown, whereas there was a positive correl ation between enzyme activity and P concentration in older needles and in needles in the lower part of the crown. In May and October, needle s of all ages showed increased acid phosphatase activity. The most sen sitive response of acid phosphatase activity to phosphate supply and p hosphorus status of the whole tree was seen in current-year needles on the first whorl where a 300% increase in acid phosphatase activity wa s observed in response to a decrease in foliar P concentration of 1.7- 1.8 mg P g(DW)(-1).