Biogeochemistry of soil phosphorus cycling in a pinyon-juniper ecosystem of the Colorado Plateau

The role of soils, microsites, and microclimate in regulating the biogeochemistry of soil phosphorus (P) was examined in a semiarid pinyon-juniper ecosystem on the Colorado Plateau. Soils and microsites determined total soil P concentrations, but did not affect microbial P. Resin and hydroxide P from a Hedley fractionation were the largest inorganic and organic P pools. The distribution of phosphorus fractions reflected the aboveground ecosystem heterogeneity only to a limited extent. In semiarid ecosystems, nutrients and microbial activity are usually concentrated under canopies of woody plants. Phosphorus distribution did not follow this general pattern.; Soil phosphatase activity reflected the heterogeneity of microsites. Alkaline phosphatase activity was significantly higher under junipers than in intercanopy areas, and exceeded acid phosphatase activity by a factor of 6. This indicates, that soil microbes are the major producers of phosphatase in the studied ecosystem. Phosphatase activities varied more than 2-fold over one year with maxima in summer and winter. Soil microclimate explained up to 20% of the variation in phosphatase activities.; Passive greenhouses were installed to simulate global warming. Greenhouses significantly raised temperatures in juniper soils during most sampling periods. Intercanopy soils were slightly cooled. There were no obvious trends in the effects of greenhouses on soil moisture. Temperature changes in greenhouse treated juniper soils were similar to those predicted due to global warming over the next decades.; Greenhouses changed P biogeochemistry in pinyon-juniper soils. Biogeochemical parameters responded to small differences in soil microclimate in a consistent pattern. Biological P was higher in warmer soils within microsites, slow cycling biogeochemical P and acid phosphatase were lower. Fast cycling geochemical P, alkaline phosphatase, and plant available P were higher in warmer soils within sites, the biological mineralization index was lower. Although not all responses were statistically significant, consistent data trends suggest that the observed responses may be ecologically significant.