Root phosphatase activity and soil organic phosphorus utilization by Norway spruce [Picea abies (L) Karst]

Activity and kinetics of root surface phosphatases of Norway spruce [Picea abies (L.) Karst], and the utilization of soluble organic phosphorus compounds were used to evaluate the role of inorganic and organic soil P in the P nutrition of 140-y-old trees. Phosphatase activities of mycorrhizal and non-mycorrhizal roots of Norway spruce were determined. Root surface phosphatase activity of non-mycorrhizal 3-month-old seedlings was greater than that of 9-month-old seedlings. The amount of phosphorus supply had no significant influence on the phosphatase activity of non-mycorrhizal roots. Fine roots of 140-y-old Norway spruce had significantly higher phosphatase activity than medium and coarse roots. The kinetics of root surface phosphatase showed two distinct phases, each having a different Michaelis-Menten equation. For low substrate concentration, a K-m value of 852 mu M and V-max value of 3.5 nmol g(-1) s(-1) was calculated. At high substrate concentration, K-m was 2381 mu M and V-max 52 nmol g(-1) s(-1). Non-mycorrhizal, as well as mycorrhizal roots, depleted the inorganic and organic P concentration of a soil extract. The rate of hydrolysis differed depending on the age of the seedlings or the thickness of tree roots. If the rate of hydrolysis of organic P and uptake of inorganic P together with field data of soil solution concentration are considered, up to 75% of the P uptake of Norway spruce may be derived from the organic fraction. Copyright (C) 1996 Elsevier Science Ltd