Field Evaluation of Wood Biochar for Promoted Growth and Carbon Assimilation of Cyclobalanopsis edithiae in Quarry Site

Anthropogenic activities, such as quarrying, result in soil degradation and loss of soil ecological functions. To promote plant growth and improve soil quality, this study evaluated the in situ application of wood biochar in a soil–plant system at a quarry site in Hong Kong. The morphological and physiological characteristics of the plants (C. edithiae), as well as carbon assimilation under biochar treatment, were investigated. Biochar derived from wood feedstock was selected and applied at a dosage of 5% by mass over a 2-year period. The study observed that biochar had a significant (p < 0.05) positive effect on the leaf area, the diameter of the stem and root of C. edithiae at the field site. Additionally, biochar significantly increased the dry biomass of the leaf, stem, and root by 225% (p < 0.01), 170% (p < 0.05) and 189% (p < 0.05), respectively. This contributed to an increase in the amount of carbon assimilated per plant seedling, rising from 56 to 159 g. The plant carbon assimilation capacity demonstrated positive relationships with plant growth and development characteristics, whereas root tensile strength was negatively correlated with them. Moreover, the biochar-treated group exhibited a 61% higher CO₂ flux at the soil surface, while CH₄ flux showed no significant changes compared to the non-biochar-treated group. This study highlighted the potential of wood biochar as an effective soil amendment for enhancing plant growth and carbon assimilation in degraded quarry sites, providing valuable insights for ecological restoration efforts.