Responses of bean ( Phaseolus vulgaris L. cv. Pros) to chronic ozone exposure at two levels of atmospheric ammonia

Abstract

Plants of bean ( Phaseolus vulgaris cv. Pros) were exposed to a range of O 3 concentrations up to 70 nl litre −1 for 9 h day −1 in the presence (45 nl litre −1) and absence (21 nl litre −1) of enhanced NH 3 in 12 open-top chambers. Treatment effects on visible injury, growth and yield were assessed after 49 (intermediate harvest) and 62 days of exposure (final harvest). The proportion of leaves with visible injury at final harvest increased with increasing concentrations of O 3. Enhanced NH 3 did not cause any symptoms and did not affect injury by O 3. The estimated seasonal mean concentration corresponding with 5% injury was circa 23 nl litre −1 O 3. Biomass production and green pod yield decreased with increasing concentrations of O 3 and were generally stimulated by enhanced NH 3 at both harvests. Adverse effects of O 3 on biomass and pod yield did not depend on the NH 3 level. Relative yield response to increasing 9-h daily mean O 3 concentrations was nonlinear and yield losses of 5 and 10% were calculated to occur at seasonal daytime mean concentrations of 27 and 33 nl litre −1 O 3, respectively. Linear regression showed that the Accumulated exposures Over a Threshold of 30 (AOT30) and 40 nl litre −1 (AOT40) O 3 performed equally well. The estimated accumulated O 3 exposures corresponding with a yield loss of 5% were 1600 nl litre −1 h for AOT30 and 400 nl litre −1 h for AOT40. The results are discussed in relation to the long-term critical level that is used as a guideline to protect crops against adverse effects by O 3.