Impact of elevated CO₂ on C:N:P ratio among soybean cultivars

Elevated atmospheric CO₂ concentration (eCO₂) exerts significant influence on nutrient requirement in plant. The investigation of C:N:P ratios in major cropping soils is important for managing nutrient balance and maximizing their use efficiency in future farming systems. This study aimed to examine the effect of eCO₂ on the C:N:P ratios in different plant parts among soybean cultivars. Twenty-four soybean cultivars were planted in open top chambers at two CO₂ concentrations (390 and 550 ppm) and sampled at the initial pod filling stage (R5) and the full maturity stage (R8). The C, N and P concentrations in root, stem, leaf and seed were determined. Elevated CO₂ decreased the N concentrations in stem (-5.1%) and leaf (-3.2%) at R5, and in root (-24%), stem (-25%) and seed (-6.2%) at R8, resulting in a significant decrease of C:N ratio in the corresponding parts. The P concentration was significantly increased in root (6.0%), stem (7.9%) and leaf (16%) at R5, and in root (2.6%), stem (29%) and seed (16%) at R8 across 24 cultivars, leading to a decrease in the C:P ratio. Elevated CO₂ significantly decreased the N:P ratio in root (-4.5%), stem (-12%) and leaf (-17%) at R5, and in root (-26%), stem (-57%) and seed (-22%) at R8. Furthermore, the response of C:N:P ratios to eCO₂ varied greatly among soybean cultivars leading to significant CO₂ × cultivar interactions. Nitrogen, but not P was the limiting factor for the soybean plants grown in Mollisols under eCO₂. The considerable variation in the C:N:P ratios among cultivars in response to eCO₂ indicates a potential improvement in soybean adaptability to climate change via selection new cultivars. Cultivars SN22 and ZH4 that did not considerably altered the C:N and C:P ratios in response to eCO₂ are likely the optimal genomes in soybean breeding programs for eCO₂ adaption.