Comparative Responses of Container‐ versus Ground‐Grown Soybean to Elevated Carbon Dioxide and Ozone

In studies of CO 2 –enrichment effects on plants, the applicability of results derived from experiments using container‐grown plants for predictions of future crop performance in a CO 2 –enriched atmosphere has been questioned. Concerns also have been expressed about plant growth studies with the air pollutant O 3 in pot‐grown plants. Further, since elevated CO 2 and O 3 co‐occur, studies are required with the combination of gases. In this 2‐yr experiment, soybean [ Glycine max (L.) Merr.] plants grown in large pots (15 and 21 L) and in the ground were exposed to mixtures of CO 2 and O 3 in open‐top chambers. The CO 2 treatments were ambient and CO 2 enrichment of approximately 337 μmol mol −1 added 24 h d −1 Ozone treatments were charcoal‐filtered (CF) air (23 nmol mol −1 ) and approximately 1.5 times ambient O 3 levels (71 nmol mol −1 ) given 12 h d −1 Relative effects of elevated CO 2 and O 3 on aboveground biomass and seed yield were quite similar for plants grown in pots compared with plants grown in the ground. Elevated CO 2 increased total seed mass and O 3 suppressed it to similar magnitudes in both rooting environments. Elevated CO 2 also reduced the toxic effects of O 3 Net photosynthesis ( A ) was similar while stomatal conductance (g s ) was higher in pot‐grown compared with ground‐grown plants, possibly due to better soil moisture status. The results indicated that planting density and rooting environment affected plant morphology, but relative responses of seed yield to elevated CO 2 and O 3 were not fundamentally different between soybean plants grown in large pots and in the ground in open‐top chambers.