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,) 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.