Elevated ozone concentration decreases whole-plant hydraulic conductance and disturbs water use regulation in soybean plants.

Elevated tropospheric ozone (O3 ) concentration has been shown to affect many aspects of plant performance including detrimental effects on leaf photosynthesis and plant growth. However, it is not known whether such changes are accompanied by concomitant responses in plant hydraulic architecture and water relations, which would have great implications for plant growth and survival in face of unfavorable water conditions. A soybean (Glycine max (L.) Merr.) cultivar commonly used in Northeast China was exposed to non-filtered air (NF, averaged 24.0 nl l-1 ) and elevated O3 concentrations (eO3 , 40 nl l-1 supplied with NF air) in six open-top chambers for 50 days. The eO3 treatment resulted in a significant decrease in whole-plant hydraulic conductance that is mainly attributable to the reduced hydraulic conductance of the root system and the leaflets, while stem and leaf petiole hydraulic conductance showed no significant response to eO3 . Stomatal conductance of plants grown under eO3 was lower during mid-morning but significantly higher at midday, which resulted in substantially more negative daily minimum water potentials. Moreover, excised leaves from the eO3 treated plants showed significantly higher rates of water loss, suggesting a lower ability to withhold water when water supply is impeded. Our results indicate that, besides the direct detrimental effects of eO3 on photosynthetic carbon assimilation, its influences on hydraulic architecture and water relations may also negatively affect O3 -sensitive crops by deteriorating the detrimental effects of unfavorable water conditions.