Coupled effects of elevated CO2 and biochar on microbial communities of vegetated soil.

Soil microbial communities are important for plant growth and establishing healthy ecosystems. Although biochar is widely adopted as a sustainable fertilizer, its influence on soil ecological functions is still unclear, especially under climate change such as elevated carbon dioxide concentration (eCO2). This study explores the coupled effects between eCO2 and biochar on microbial communities in soil planted with tree seedlings of Schefflera heptaphylla. Root characteristics and soil microbial communities were examined and interpreted with statistical analysis. Results show that biochar application at ambient carbon dioxide concentration (aCO2) always improves plant growth, which is further promoted under eCO2. Similarly, ß-glucosidase, urease and phosphatase activities are enhanced by biochar at aCO2 (p < 0.05). In contrast, only urease activity increases with biochar added at eCO2 (p < 0.05). The beneficial effects of biochar on soil enzyme activities become less significant at eCO2. Depending on biochar type, biochar can increase bacterial diversity and fungal richness at aCO2. However, at eCO2, biochar does not significantly affect microbial richness (p > 0.05) while microbial diversity is reduced by peanut shell biochar (p < 0.05). Owing to better plant growth under biochar application and eCO2, plants are likely to become more dominant in specializing the microbial communities that are favourable to them. In such community, the abundance of Proteobacteria is the greatest and increases after biochar addition at eCO2. The most abundant fungus also shifts from Rozellomycota to Ascomycota and Basidiomycota. These microbes can improve soil fertility. Even though the microbial diversity is reduced, using biochar at eCO2 can further promote plant growth, which in turn enhances carbon sequestration. Thus, biochar application can be an effective strategy to facilitate ecological restoration under climate change and relieve the problem of eCO2.

Intercropping of Pinellia ternata (herbal plant) with Sedum alfredii (Cd-hyperaccumulator) to reduce soil cadmium (Cd) absorption and improve yield.

Soil contamination by cadmium (Cd) is of global concern, threatening not only crop production, but also supply of herbal medicine. Research studies usually grow crops with Sedum alfredii (a Cd-hyperaccumulator). However, intercropping herbal plants with S. alfredii and their interactions with hydro-chemical properties of soil are rarely considered. This study examines the growth of a herbal plant, Pinellia ternata, intercropped with S. alfredii in Cd-contaminated soil. Plant characteristics were assessed, especially biomass and Cd content of bulbil (yield and quality of P. ternata). Soil hydro-chemical properties including water retention, Cd content and organic matter were determined with statistical analyses. At low soil-Cd contamination (0.6 µg/g), bulbil biomass of intercropped P. ternata (PSL) was almost double compared with monoculture of P. ternata (PL), which is barely significant (p ≈ 0.05). The corm biomass of PSL was also significantly greater than that of PL (p < 0.05). Although soil-Cd contamination became more severe by increasing to 3 µg/g, the bulbil biomass in the intercrop was not significantly different from PL (p > 0.05). That said, it is evidenced that the yield of intercropped P. ternata was improved in Cd-contaminated soil. Such improvement was mainly attributed to reduced soil-Cd content and enhanced soil-water retention which was governed by plant roots and soil organic matters. The soil-water retention was first identified as a critical parameter in promoting plant growth under intercropping. More importantly, the bulbil-Cd content of P. ternata in PSL was significantly reduced (p < 0.05). This study demonstrates that the newly proposed intercrop is feasible to improve yield of herbal plants, and at the same time reduce heavy metal absorption and accumulation in medicinal organs, especially for P. ternata. This is anticipated to reduce the human health risk imposed by ingestion of Chinese herbal plants.

Effects of biochar on shear strength of completely decomposed granite.

Biochar has a great potential to sustainably improve the performance of bio-engineered slope due to its ability to retain water and to supply nutrients. Existing studies mainly focus on hydrological properties of biochar-amended soil. However, the effects of biochar on shear strength of soil are not well studied. This study aims to assess the shearing behaviour of biochar-amended completely decomposed granite (CDG). Soil specimens were prepared by mixing CDG with two types of biochar at a mass ratio of 5% and compacted at 95% of the maximum dry density. Although the peak shear strength of biochar-amended CDG is reduced by up to 20% because of lower initial dry density of the soil and crushing of biochar particles during shearing, both types of biochar have negligible effects on the ultimate shear strength, which is governed by friction between soil particles. This highlights that the ultimate friction angle can be adopted for designing bio-engineered slopes using biochar-amended soils.