Soil biochemical activity and phosphorus transformations and losses from acidified forest soils

Three Bohemian Forest catchments, Plešné, Černé and Čertovo, were studied. These catchments have similar climatic conditions, relief and vegetation, but differ in their bedrock composition. The granitic bedrock in the Plešné catchment was more susceptible to phosphorus (P) leaching under acid conditions than was the mica schist bedrock in the other catchments. The goal of this study was to determine if higher P leaching from the Plešné catchment was associated with differences in microbial P transformations and enzymatic P hydrolysis. Phosphorus and nitrogen contents in soil microbial biomass (PMB, NMB; chloroform fumigation), C mineralisation rate (Cmin; CO2 production by GC) and phosphatase activity (MUF-phosphate), were measured in three successive years. Phosphatase activity, PMB, and Cmin were used to characterise the enzymatic hydrolysis of organic P, microbial P accumulation, and microbial mineralisation rates of organic compounds, respectively. Soil chemical properties were characterised by C, N and P content, pH, and by oxalate-extractable P, Fe and Al. Spatial variability in NMB, PMB, Cmin and phosphatase activity within the catchment was higher (coefficient of variation, CV<50%) than their temporal variability (CV<30%). Multivariate analysis revealed a significant soil layer effect but not that of catchment. When soil layers were evaluated separately, a difference between the Plešné and Černé or Čertovo catchments was found in litter and mineral layers, even though the variability within one catchment was high. Within soil profile, phosphatase activity was positively correlated with Ctot, NMB and Cmin (r2=0.89–0.92) being very correlated with PMB (r2=0.99). Phosphatase activity was higher in the litter (14.0 nmol g−1 h−1) and humus (8.65 nmol g−1 h−1) layers of Plešné than in the same layers of the Černé (9.65 and 6.40 nmol g−1 h−1) and Čertovo (12.8 and 6.0 nmol g−1 h−1) soils. Similarly, PMB in the litter and humus layers of Plešné soil (161 and 93 μg g−1) was higher than PMB of the same layers of the Černé (120 and 66 μg g−1) and Čertovo (148 and 89 μg g−1) soils. High MUFP hydrolysis rate: Cmin molar ratio (0.16–1.17 M of P per 1 M of respired C) indicated that potential enzymatic P hydrolysis exceeded estimated microbial P demand (0.034 M of P per 1 M of respired C) in all catchments. The results suggest that higher microbial P transformations and enzymatic P hydrolysis could contribute to enhanced P leaching from the Plešné catchment, which could be enhanced by the lower Fe content in the soil of this catchment as compared to the Černé and Čertovo catchments.