Drivers of the variability of soil phosphorus fractions in boreal forested watersheds

In the boreal forest, phosphorus (P) is tightly cycled and can be heterogenous in its distribution across the landscape. Characterizing chemical, physical, and landscape-scale drivers of variability in both concentration and forms of soil P can help us understand how P dynamics will respond to environmental change; however, data on forms of soil P in boreal forests are sparse. The goal of this study was to assess the variability of soil P across a boreal forested watershed. Seventy-four surface soil samples from a boreal forested catchment were analyzed for a suite of chemical and physical characteristics, and were paired with geospatial data to develop predictive models of forms of soil P. Water-extractable P concentrations were low, while total P (65.7–2197 mg kg −1 ) and plant-available (Mehlich-3-extractable) P (0.63–193 mg kg −1 ) concentrations varied widely across the study area. Partial least squares regression results indicated that plant-available P was strongly related to soil Mn and Ca content, while total P was more strongly related to organic C and wetness index. These results suggest that soil P can vary widely, even in nutrient-poor boreal ecosystems, and site-specific characteristics may play an important role in predicting variability.