Since most commercially grown soybean plants in the USA are subjected to low or moderate levels of ambient O3 pollution it is important to understand whether exposure to O3 influences CO2 exchange in this species. Therefore, for 8 weeks soybean (Glycine max cv. Hodgson) plants were exposed to O3 for 6.8 h daily in controlled environment chambers. Four treatments were used: 0.01, 0.05, 0.09, and 0.13 μL L-1 O3 in filtered air. Net photosynthesis (P(n)), dark respiration, and chlorophyll content were measured in all treatments for both individual leaves of various ages and for whole plants. Measurements of CO2 exchange were made nondestructively with an infrared gas analysis system using either plexiglass cuvettes (leaves) or continuously stirred tank reactors (plants). The P(n) of whole plants was reduced by 10, 11, and 22% in the 0.05, 0.09, and 0.13 μL L-1 treatments, respectively, compared with the 0.01 μL L-1 treatment. Among individual leaves of similar ages, exposure to O3 also resulted in declines in P(n) and this occurred at all leaf ages. There was a significant linear relationship between P(n) and O3 concentration for both individual leaves and for whole plants. Chlorophyll contents of whole plants and individual leaves were also reduced by O3 exposure. Chlorophyll content and P(n) were correlated with each other for both individual leaves and whole plants. Changes with leaf age were typical for P(n) and for chlorophyll content. There was no apparent effect of O3 treatment on dark respiration. The observed reduction in P(n) at low levels of O3 (coupled with reports of O3-induced reduction in growth and yield) suggests that ambient O3 pollution in the USA is currently causing decreased P(n) in field-grown soybean which can lead to a significant loss in yield.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Environmental Quality|
|State||Published - Jan 1 1986|