Phosphatase activity, microbial phosphorus, and fine root growth in forestsoils in the Sierra de Gata, western central Spain

Acid phosphatase activity (APA), labile P fractions and fine root growth we re studied in an oak (Quercus pyrenaica Willd.) forest in the Sierra de Gat a, in western central Spain. Soils in the region are acid and rich in organ ic matter, with low levels of extractable inorganic P but with a high propo rtion of organic P In such soils, the activity of phosphatase enzymes is li kely to be important for the control of P mineralization and P cycling and, consequently, can affect the availability of P for plant uptake. The bioma ss of fine roots was about 25-fold that of leaf litter, demonstrating a hig h allocation of C resources to the root system in order to compensate for a low availability of soil nutrients. The study compared plots fertilized wi th triple superphosphate (100 kg P ha(-1)) to control (unfertilized) plots. Fertilizer application had no significant effect on APA and fine root dens ity; however, there were significant differences in available and microbial P. Spatial and seasonal variations in the APA were related to plant root d ensity and biotic demand. Seasonal differences in the APA may also be the c onsequence of changes in the amount of hydrolysable organic substrates at d ifferent times of the year.