Synergistic effects of biochar application and elevated atmospheric CO₂ concentration on rice biomass allocation and yield

Objectives Elevation of atmospheric CO₂ concentration affects the photosynthesis of crops, and the application of biochar is beneficial to the root growth of crops. This paper investigates the interaction effects of elevated CO₂ and biochar application to reference proper nutrient management for increasing elevated CO₂ concentration in the future.

Methods A pot experiment was conducted in Changping, Beijing, using Jijing 88 as rice variety. There were 4 treatments in the experiment: normal ambient CO₂ concentration without biochar (CK) and with biochar (B), and high CO₂ concentration without biochar (F) and with biochar (F + B). The normal and high atmospheric CO₂ concentrations were 400 µmol/mol and 550 µmol/mol, and the biochar application rate was 20 g/kg. Rice samples were collected at the tillering, jointing, heading, and maturity stage to determine plant height and biomass distribution. Yield and yield components were investigated at harvest.

Results Compared with CK, treatment B significantly increased rice plant height at tillering, joingting and heading stage, but not at the maturing stage, while treatment F and F + B did not significantly increase plant height at all the four stages. B, F, and F + B treatments all increased total dry weight of single stem, leaf, root system, and above-ground biomass of rice at the stages under consideration. The total dry weight of rice leaf, root system and above-ground biomass was higher in biochar (B) and high-concentration CO₂ (F) alone; F + B treatment only had a significantly (P < 0.05) impact on the dry weight of roots. Compared with the control (CK), there was no interaction effect (P > 0.05) on the rice root-to-shoot ratio at the tillering stage. However, the values increased by 10.7% at the heading stage, decreased by 5.0% at the jointing stage, and by 12.7% at the maturity stage. Application of biochar (B) and elevated CO₂ concentration (F) (P < 0.05) increased rice ear length, grain number, and one thousand-grain weight. Rice yield showed an increasing trend under the interaction of biochar and elevated CO₂; however, the interaction effect was significant on one thousand-grain weight only.

Conclusions High-concentration CO₂ and biochar show a significant positive interaction effect on rice growth and yield components. Increasing atmospheric CO₂ concentration is beneficial to the growth and dry matter accumulation of rice plants above and below ground, but it reduces the seed setting rate and yield. Combined application of biochar under high CO₂ concentration not only promotes plant growth and dry matter accumulation, but also significantly increases yield components, showing a good interaction effect.