Soybean and soil responses to biochar amendment in controlled environments with elevated temperature and carbon dioxide

Warmer atmospheric temperatures (eT) will increase plant nutrient uptake, and elevated atmospheric CO₂ (eCO₂) is expected to enhance plant growth, whereas a multicomponent eTeCO₂ effect should also be beneficial for agroecosystems. Our goal was to understand if single- (eT, eCO₂) or multicomponent (eTeCO₂) climate effects, predicted for southern Ontario, Canada, will affect soybean and soil properties differently when soil is amended with manure and biochar (MB) or with manure, nitrogen (N) fertilizer, and biochar (MNB) compared with the addition of manure and N fertilizer (MN). We hypothesized that biochar regulates climate effects and causes soybean and soil properties to be similar to ambient climate conditions than soil without biochar. However, soil amended with biochar functioned independently of single- or multicomponent climate effects. Soybean pod and shoot biomass, shoot height, and shoot:root ratio were greater (p < 0.05) with eT. eCO₂ increased (p < 0.05) shoot biomass coinciding with an increase (p < 0.05) in nutrient uptake and uptake efficiency. All climate effects decreased (p < 0.05) soluble carbon (C), available N (NH₄⁺ and NO₃⁻), and the C/N ratio but increased (p < 0.05) orthophosphate. Amendment type MNB decreased (p < 0.05) soil microbial biomass carbon, but climate effects did not affect microbial biomass (p < 0.05). However, climate effects influenced how C and N were accessed by microbes in all amendment types, shifting (p < 0.05) microbial community structure, species richness, and diversity. We rejected our hypothesis and concluded that biochar amended soil does not strongly influence soybean and soil properties, and it does not provide a greater ability for soybeans and soil to cope with climate effects.