NO2 and SO2 mixtures stimulate barley grain production but depress clover growth
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Cereals and legumes contrast sharply in their nitrogen metabolism. Nitrogen-fixing legumes have a ready source of nitrogen due to the activities of nitrogen-fixing bacteria, but cereals must meet their nitrogen requirements by direct root uptake from the soil. These differences in access to nitrogen may influence their responses to exposure to NO2 and SO2. To determine whether this occurs, the influences of SO2 and NO2 on growth,and yield of a cereal (barley) and a legume (clover) were studied. Plants were exposed to <5, 55, 149, 262 or 544 nl/l of SO2, and <5 or 170 nl/l of NO2 for 4 hr/day for 108 days in a factorial experiment using outdoor open-top chambers. NO2 halved plant dry weight in clover but under the same conditions, it increased plant dry weight in barley by increasing ear weight, and grain number and weight. However it decreased leaf total S concentration in both species, and grain protein concentration in barley. When barley or clover were exposed to SO2 alone, growth decreased as SO2 concentration increased. Large decreases occurred in total above-ground plant weight of both barley and clover, and ear number and weight, and grain number and weight of barley. In both species, SO2 resulted in a three-fold increase in the foliar S concentration until saturation at 149 nl/l. Barley grain protein concentration was also increased by SO2. In contrast to the effects of the gases applied separately, mixtures of NO2 and 55 or 149 nl/l of SO2 substantially increased barley grain production while having no significant effect on vegetative growth. SO2 concentrations of up to 149 nl/l modified growth of clover, decreasing shoot dry weight, but increasing shoot length. It was concluded that the differences observed between the responses of barley and clover to SO2 and NO2 mixtures are likely to be attributable to differences in their access to nitrogen. Increased grain production in barley exposed to mixtures of SO2 and NO2 appears to be a partial expression of a response involving the detoxification, allocation, transport, use and storage of SO2 and NO2 derivatives.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||School of Biological and Environmental Sciences|
|Copyright:||© 1992 Elsevier B.V.|
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