Lithology and bioclimate impacts on soil organic phosphorus speciation and the relationship between phosphatase and organic phosphorus in California temperate forest

The dynamic equilibrium between soil phosphatase activities and soil organic phosphorus (P_o) species can be impacted by soil forming factors. While much research has addressed soil P_o dynamics as a function of time using chronosequences, understanding of lithology and bioclimate impacts on soil P cycling remains comparatively limited. We tested hypothesized interactive impacts of lithology and bioclimate on the quantity and quality of soil P_o, and relationships between P_o composition and phosphatase activities using a full factorial combination of three lithologies (andesite, basalt, granite) and four bioclimatic zones (blue oak, ponderosa pine, white fir, red fir) constrained by elevation ranges across the Sierra Nevada and southern Cascades in California, USA. Activities of acid and alkaline phosphomonoesterase (PME) and phosphodiesterase (PDE) were positively associated with concentrations of P_o species determined by NaOH-EDTA extraction and solution ³¹P nuclear magnetic resonance (NMR) spectroscopy. Concentrations of P_i and P_o species and species class (i.e., phosphomonoesters, phosphodiesters) were positively related to PME activities, whereas PDE activity was correlated to P species concentrations at species class level of phosphodiesters. Soil inositol hexakisphosphate (IHP) and most non-IHP monoesters (e.g., glucose-6′ phosphate, α- and β-glycerophosphate, phosphocholine), phosphodiesters (i.e., deoxyribonucleic acid), and inorganic phosphates (i.e., (pyro)phosphate) were 68–232 % higher in soils developed on andesite (monoester 312 mg kg⁻¹; diester 25 mg kg⁻¹), followed by basalt (monoester 174 mg kg⁻¹; diester 20 mg kg⁻¹), and lowest in granite (monoester 133 mg kg⁻¹; diester 12 mg kg⁻¹), reflecting greater contents of poorly crystalline Fe/Al oxides and P from intermediate parent materials. Bioclimatic impacts on concentrations and proportions of P_o species were highly specific to lithology, with P species concentrations lowest at the highest elevation (red fir) for andesite- (monoester 265 mg kg⁻¹) and basalt-derived soils (monoester 67 mg kg⁻¹), whereas P concentrations in granite-derived soil (monoester 108–183 mg kg⁻¹) were largely uninfluenced by bioclimate. Relationships among phosphatase activities and P_o species concentrations were mainly observed in mafic material-derived soils, and were highly specific to P species at a given bioclimate. Integrating lithology and bioclimate context may enable more comprehensive assessments of soil P cycling.