Phosphorus mineralization and microbial biomass in a Florida Spodosol: effects of water potential, temperature and fertilizer application

Phosphorus mineralization and microbial biomass were measured in the surfac e 5 cm of a Spodosol (sandy, siliceous hyperthermic Ultic Alaquod) from nor th-central Florida. Soils from fertilized and unfertilized plantations of l oblolly pine (Pinus taeda L.) were incubated at a range of water potentials (similar to 0, -3, -8, -10 and -1500 kPa) and temperatures (15 degrees C, 25 degrees C and 38 degrees C) for 14 days and 42 days. increasing water po tential and temperature increased specific P mineralization (mineralization expressed as a percentage of total P) regardless of fertilizer treatment. An increase in water potential from -10 kPa to -0.1 kPa resulted in an incr ease of between 38% and 239% in the concentration of KCl-extractable inorga nic P, depending on incubation temperature and time. An increase in incubat ion temperature from 15 degrees C to 38 degrees C resulted in an increase o f between 13% and 53% in KCl-extractable inorganic P. Changes in specific P mineralization with change in water potential or temperature were not affe cted by fertilizer application. This suggests that, although specific P min eralization was greater in the fertilized soils, environmental control of P mineralization was the same for both treatments, Specific P mineralization was most sensitive when soils were at higher water potentials, and decreas ed logarithmically to water potentials of between -3 kPa and -8 kPa. Specif ic P mineralization was relatively insensitive to changes in water potentia l when water potential was lower than -8 kPa. Microbial biomass C showed no consistent responses to changes of temperature or water potential and was not significantly correlated with specific P mineralization. Our results su ggest that field estimates of P mineralization in these Spodosols may be im proved by accounting for changes in soil water potential and temperature.