Interactive Effects of Carbon Dioxide and Phosphorous Nutrition On Soybean Growth and Development.

The crop demand for nutrients such as phosphate (Pi) might be higher due to the introduction of high yielding cultivars and increased plant growth under rising atmospheric carbon dioxide (CO₂) concentration. To evaluate the interactive effects of Pi nutrition and CO₂ conc., soybean plants were grown in controlled environment growth chambers with sufficient (0.50 mM) and deficient (0.10 and 0.01 mM) Pi supply under ambient and elevated CO₂ (400 and 800 μmol mol^-1,  respectively). Phosphate deficiency decreased in the number of mainstem nodes (6-10%), leaf area (44-53%), total biomass (30-48%), and seed weight (47-60%) at both CO₂ treatments. The degree of growth stimulation (0 – 55% biomass) by elevated CO₂ was dependent upon the severity of Pi deficiency and was closely associated with the increased phosphorus utilization efficiency for biomass production. The increased tissue nitrogen (N) conc. in Pi-deficient plants might be attributed to the increased nutrient uptake due to large increase in the fraction of root mass to the total biomass. The tissue P and N conc. tended to be lower under elevated CO₂ and did not appear to be the main cause of the lack of growth and P_net response to elevated CO₂ under Pi deficiency. The critical leaf phosphorus conc. was generally lower at elevated CO₂ except for photosynthetic processes. Overall, plant biomass and seed yield parameters showed higher critical leaf P conc. (2.8 – 2.94 mg g^-1) followed by gas exchange and fluorescence parameters (1.59 – 2.76 mg g^-1) and the lowest for plant height and node development (0.76 – 1.16 mg g^-1).