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Growth, nutrient dynamics, and efficiency responses to carbon dioxide and phosphorus nutrition in soybean

Plant mineral nutrients such as phosphorus may exert major control on crop responses to the rising atmospheric carbon dioxide (CO2) concentrations. To evaluate the growth, nutrient dynamics, and efficiency responses to CO2 and phosphorus nutrition, soybean (Glycine max (L.) Merr.) was grown in controlled environment growth chambers with sufficient (0.50 mM) and deficient (0.10 and 0.01 mM) phosphate (Pi) supply under ambient and elevated CO2 (aCO2, 400 and eCO2, 800 µmol mol−1, respectively). The CO2 × Pi interaction was detected for leaf area, leaf and stem dry weight, and total plant biomass. The severe decrease in plant biomass in Pi-deficient plants (10–76%) was associated with reduced leaf area and photosynthesis (Pnet). The degree of growth stimulation (0–55% total biomass) by eCO2 was dependent upon the severity of Pi deficiency and was closely associated with the increased phosphorus utilization efficiency. With the exception of leaf and root biomass, Pi deficiency decreased the biomass partitioning to other plant organs with the maximum decrease observed in seed weight (8–42%) across CO2 levels. The increased tissue nitrogen (N) concentration in Pi-deficient plants was accredited to the lower biomass and increased nutrient uptake due to the larger root to shoot ratio. The tissue P and N concentration tended to be lower at eCO2 versus aCO2 and did not appear to be the main cause of the lack of CO2 response of growth and Pnet under severe Pi deficiency. The leaf N/P ratio of >16 was detrimental to soybean growth. The tissue P concentration needed to attain the maximum productivity for biomass and seed yield tended to be higher at eCO2 versus aCO2. Therefore, the eCO2 is likely to increase the leaf critical P concentration for maximum biomass productivity and yield in soybean.