Nucleic acids are a major pool of hydrolyzable organic phosphorus in arable organic soils of Southern Ontario, Canada

Abstract

Soil organic phosphorus (P_o) that is hydrolyzed by phosphatases into inorganic phosphate is a source of phosphorus (P) for agricultural crops. However, the hydrolysis of P_o compounds is contingent on their chemical form and stabilization in the soil matrix. We quantified three hydrolyzable P_o pools (simple phosphomonoesters, phospholipids, and nucleic acids) by adding substrate-specific phosphatases to Hedley sequentially fractionated extracts from three organic soils cultivated with carrots in Southern Ontario, Canada. We observed that most of the molybdate-unreactive P was hydrolyzable in the deionized water, 0.5 mol L⁻¹ NaHCO₃, and 0.1 mol L⁻¹ NaOH P pools (67–92%) and accounted for 14–254 kg P ha⁻¹ in these arable organic soils. Nucleic acids represented 79% of the hydrolyzable P_o in these soils but were mostly found in the 0.1 mol L⁻¹ NaOH P pool (89%), suggesting that this P_o form is bound to the soil matrix, probably to organic complexes based on the strong association between nucleic acids and total organic C (ρ = 0.805). Therefore, we propose that nucleic acids are a major hydrolyzable P_o pool that are stabilized by the organic C contained in the organic soils of this study. This P_o compound class should be considered in the P_o biogeochemical cycle of these soils.