Phosphatase activity and P fractions in soils of an 18-year-old Chinese fir ( Cunninghamia lanceolata) plantation

Abstract

Chinese fir ( Cunninghamia lanceolata), an important native tree species, has been widely planted in mountainous areas in the tropics and subtropics in China for more than 1000 years and used for a variety of wood products. The rate of phosphorus (P) supply is the most limiting factor to primary productivity in many Chinese fir plantation ecosystems. Soil phosphatase activity can be a good indicator of the organic P mineralization potential and biological activity of soils. Acid and neutral phosphatase activity (APA and NPA, respectively) and P fractions in the soils of an 18-year-old Chinese fir plantation in southwestern China were investigated. APA, 181.2 mg phenol kg −1 h −1, was significantly higher than NPA, 80.7 mg phenol kg −1 h −1, in the rhizosphere and bulk soils. In comparing rhizosphere soils and bulk soils at 20, 40, and 80 cm from the tree stem, phosphatase activity significantly decreased with the distance from the tree stem. APA and NPA decreased with soil depth, highest in the soil A horizon and least in the C horizon. Total and organic P, dilute acid extractable P (DA-P), aluminum bound P (Al-P) and iron bound P (Fe-P) in the rhizosphere were significantly higher than in soils at 20, 40 and 80 cm from the tree stem, whereas calcium bound P (Ca-P) was significantly lower. All P fractions significantly decreased with soil depth except for Ca-P. APA and NPA were significantly correlated to total P, inorganic P, organic P and occluded Fe/Al bound P, Al-P, Fe-P as well as Ca-P. These results suggested that organic P compound is used as a P source in Chinese fir plantations deficient in P in southern China, and that the application of organic phosphate fertilizer is effective around trees and in the soil surface horizons.