Phosphorus fractions and phosphatase activity in an Andisol under different forest ecosystems

Total phosphorus (P), Olsen P, microbial P and different labile P fractions determined by a modified Hedley procedure, together to acid phosphatase (P-ase), pH and organic C, were analyzed in soil from four Nothofagus rainforest ecosystems differing in forest type and management. The sites included two evergreen (EF) and two secondary deciduous (DF) rainforests growing in an Andisol of southern Chile. Samples were collected from the organic layer and from mineral soil at 2–20 cm depth. Total P and phosphorus fractions were highest in evergreen forest soil with the predominance of moderate labile (NaOH–Po) fraction. Olsen P, microbial P, labile P fractions, inorganic P fractions and acid phosphatase were greater in the organic layer than the mineral soil, especially under evergreen forests. Evergreen forest litter affected P cycling enhancing P lability and P-ase activity in soil. Forest management affected P fractions in EF but not in DF forests, and generally did not modify soil properties. Results show that clearing of deciduous forest did not seriously affect the P cycle in this Andisol and confirm the fundamental role of the organic layer in P conservation of these ecosystems.