Lithological and bioclimatic impacts on soil phosphatase activities in California temperate forests

Abstract

Organic phosphorus (Po) biogeochemical cycling is known to be impacted by soil-forming factors, yet little is known about interactions among soil-forming factors on the drivers of Po cycling, soil phosphatases. A comprehensive assessment of lithological and bioclimatic impacts on soil phosphatase activities was conducted using lithological and vegetation-constrained climatic (i.e., bioclimatic) gradients in temperate California forests. Soils (0–5, 5–15 cm depth) from twelve combinations of three lithologies (andesite, basalt, granite) and four bioclimatic zones (blue oak, ponderosa pine, red fir, white fir) encompassing a wide range of MAP (330–1400 mm) and MAT (5.0–17.0 °C) were analyzed for resin P (Presin), Po, microbial biomass P and total P (Pt), activities of three phosphatases, and soil properties (e.g., organic carbon [OC], pedogenic minerals). Across soil depths, lithology influenced phosphomonoesterase (ACP, ALP) activities more than bioclimate, whereas the opposite occurred for phosphodiesterase (PDE). Correlations of phosphatases with edaphic (e.g., pedogenic minerals, clay content) and climatic variables (MAP, MAT) varied by lithology (e.g., ACP and OC, Rbasalt = 0.61, p < 0.01 and Rgranite = 0.20, p = 0.28), indicating lithological dependence of bioclimatic impacts. Within bioclimates, phosphomonoesterase but not PDE activities were correlated with OC much more strongly than with pedogenic minerals, suggesting limited lithological impacts in vegetation- and climate-constrained ecosystems. This study demonstrates that the enzymes that catalyze the two distinct steps of Po mineralization, phosphomonoesterase versus phosphodiesterase, can express differential and even opposite relationships with edaphic variables depending on the combination of lithology and bioclimate. Additionally, OC, Presin, and Po may not necessarily be the best predictors of phosphatase activities as commonly proposed. Lithology type and/or pedogenic minerals that integrate lithology and bioclimate context may enable a more comprehensive assessment of phosphatases in soil P cycling sensitive to bioclimatic variability.