Biochar has been used as a sustainable soil amendment for different engineering applications in degraded land and as a strategy for addressing climate change issues. The underlying mechanisms of soil-plant interactions in response to biochar implementation are not yet fully understood, particularly under future condition of elevated atmospheric CO₂ (eCO₂) concentration. Moreover, the assessment of long-term effects of biochar on ecological restoration of degraded land is limited. Thus, this study aims to investigate (i) effects of biochar types on plant performance, (ii) soil-plant interactions under elevated CO₂ concentration and (iii) effects of biochar on ecological restoration in degraded land, such as plant and microbial community establishment.

A series of laboratory experiments w...[ Read more ]

Biochar has been used as a sustainable soil amendment for different engineering applications in degraded land and as a strategy for addressing climate change issues. The underlying mechanisms of soil-plant interactions in response to biochar implementation are not yet fully understood, particularly under future condition of elevated atmospheric CO₂ (eCO₂) concentration. Moreover, the assessment of long-term effects of biochar on ecological restoration of degraded land is limited. Thus, this study aims to investigate (i) effects of biochar types on plant performance, (ii) soil-plant interactions under elevated CO₂ concentration and (iii) effects of biochar on ecological restoration in degraded land, such as plant and microbial community establishment.

A series of laboratory experiments were conducted to explore effects of biochar on soil-plant interactions and microbial communities. Five types of biochar were added at 5% mass ratio and three vegetation species (Rhodomyrtus tomentosa, Cyclobalanopsis edithiae, and Schefflera arboricola) were selected to observe the variation of plant height, leaf area and biomass etc. Then, the coupled effects of biochar and eCO₂ on soil-plant hydraulic interactions and microbial communities were investigated for S. arboricola. A two-year long-term field study was conducted in Lam Tei quarry site for evaluating biochar effects on ecological restoration by measuring plant height and soil microbial community.

The laboratory test results show that wood biochar is suitable for the growth of R. tomentosa and C. edithiae, while peanut shell biochar significantly stimulates S. arboricola growth under 400 ppm CO₂ concentration. These two types of biochar with higher pore volume and large surface area induced greater soil water retention might be the reason for this result. When the CO₂ concentration rising to 1000 ppm, plant transpiration increased. However, the benefits of eCO₂ on plant transpiration were limited by soil water content when soil suction is higher than 550 kPa, which can be solved by biochar application. In addition, the coupled effects of biochar application and eCO₂ stimulates plant growth by helping plants to specialize and establish favourable microbial communities in the soil.

The field test results showed that the variation of soil chemical properties has influenced on the growth of both shrub and tree species after wood biochar application. The growth of shrub species is enhanced by wood biochar after 18 months, which is related to the increase in microbial diversity. On the other hand, the relative abundance of Proteobacteria decreased by 12%, while the Actinobacteria abundance increased by 23% after 2 years restoration. This illustrated that ecological role of Actinobacteria becomes dominant and leads to fewer soil pathogens for plant development. Plant root growth stimulates the amino acid transport and metabolism in all soil treatments thereby accelerating ecological restoration. Moreover, the enhancement of soil nutrient cycling in Lam Tei quarry site revealing that the ecological restoration has been successfully established.