Plant–soil interaction affects the mineralization of soil organic carbon: evidence from 73-year-old plantations with three coniferous tree species in subtropical Australia

Purpose Plantation is an important strategy for forest restoration and carbon (C) storage. Plantations with different tree species could significantly affect soil properties, including soil pH, soil nutrient content, soil microbial activities, and soil dissolved organic C. Changes in these abiotic and biotic factors could regulate mineralization of soil organic C (SOC). However, it remains unclear to what extent these factors affect the mineralization of SOC under different tree species plantations. Materials and methods Soil was collected at 0–10 cm depth from plantations with Pinus elliottii Engelm . var . elliottii , Araucaria cunninghamii , and Agathis australis , respectively, in southeast Queensland, Australia. Soil samples were assayed for soil organic C; organic N and mineralization of SOC; soil particle size; total C, N, and P; and pH. In addition, a 42-day laboratory incubation with substrate additions was done to examine the influence of different substrates and their combinations on bio-available organic C. Results and discussion Our results suggested that SOC mineralization was mainly determined by soil pH and soil C content among plantations with different tree species, whereas SOC mineralization was not correlated with soil N and P contents. These results were further confirmed by the substrate addition experiments. SOC mineralization of soils from slash pine showed greater response to C (glucose) addition than soils from other two plantations, which suggested significant differences in SOC mineralization among plantations with different tree species. However, neither N addition nor P addition had significant effects on SOC mineralization. Conclusions Our results indicated that plantations with different tree species substantially affect the mineralization and stability of soil organic C pool mainly by soil pH and soil C content.