Soil phosphorus and biomass carbon co-determine plantation soil organic carbon density: a case study in western Beijing, China

Abstract

Context Studies of afforestation have traditionally neglected the influences of plant microhabitats on the growth and carbon sink capacities of planted forests. Aims We investigated the potential mechanisms related to the relationship of afforestation elevation to soil organic carbon density (SOCD). Methods The carbon density of three plantation ecosystems and barren land soils were evaluated at two elevations in the Donglingshan Mountains of Beijing, with structural equation modelling and variation partitioning analyses used to identify the environmental factors that influenced the carbon densities of plantation ecosystems. Key results Afforestation elevation was related to the vegetation phenology of plantation forests. Specifically, growth periods at higher elevations were delayed relative to those at lower elevations, while different growth periods affected growth rate of diameter at breast height (RDBH), in addition to the carbon and nitrogen contents of ground surface litters. Consequently, lower elevation afforestation reduced the carbon sink capacity of coniferous plantation ecosystems in the study area. Lower plantation elevations were associated with significantly reduced RDBH values of Pinus tabuliformis. Further, biomass carbon density (BCD) and SOCD of Larix principis-rupprechtii plantations were significantly lower due to decreased elevations. Soil nitrogen concentrations, litter nitrogen density (LND), soil phosphorus concentrations, and BCD were the primary drivers of plantation SOCD. Conclusions Overall, different plantation elevations were associated with different vegetation phenologies and RDBH values, which further affected LND and BCD, thereby ultimately affecting variation of SOCD. Implications This study provides important insights into the selection of afforestation plots to maximise plantation carbon sequestration capacities.