Topsoil phosphorus signature in five forest types along an urban-suburban-rural gradient in Nanchang, southern China

Abstract

Conversions from rural to urban land uses have the potential to greatly modify soil phosphorus (P) levels. Soils in shrubs, Masson pine forest, conifer and broadleaf mixed forest, evergreen broadleaved forest and bamboo forest in the mid-subtropical region along an urban-rural gradient in Nanchang City, southern China, were analyzed for total P and P fractions using the modified Hedley P sequential fractionation method. Results show that the topsoil total P and total exactable P concentrations were significantly higher in the urban area (0.71 g·kg⁻¹ and 378.50 mg·kg⁻¹, respectively) than in the suburban (0.30 g·kg⁻¹ and 150.74 mg·kg⁻¹, respectively) and rural areas (0.31 g·kg⁻¹ and 147.38 mg·kg⁻¹, respectively) (p<0.05). Among the five P fractions of resin-P, NaHCO₃-P, NaOH-P, Sonication-P and HCl-P, the relative abundance of HCl-P in urban forest soils (36%) was the highest and also significantly higher than in suburban (8%) and rural soils (6%), while NaOH-P was the dominant form in suburban (41%) and rural soils (50%). Phosphorus accumulation in the urban soils could affect the cycle of P in urban forest systems, particularly the HCl-P fraction that might rapidly enrich aquatic systems in urban areas.