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

Abstract

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 μM and V max value of 3.5 nmol g −1 s −1 was calculated. At high substrate concentration, K m was 2381 μM 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.