Nodule Activity in Soybean Cultivars Exposed to Ozone and Sulfur Dioxide

Abstract

AbstractIn an effort to obtain a greater understanding of the mechanisms of action for air pollutants on yield‐limiting processes in crop plants, studies were conducted in the field and greenhouse in 1979 to investigate the effects of O3 and SO2 exposures on nodule activities in roots and chlorophylls a and b contents in leaves of soybeans [Glycine max (L.) Merr.]. Six cultivars of soybeans were exposed 4 h d−1 for 5 successive days during flowering and pod development to the combination of 6.7 µmol m−3 O3 and 11.1 µmol m−3 SO2 in activated charcoal‐filtered air. Acetylene reduction procedures were used to assay nodule activities.Significant differences (P < 0.1) were observed in total nodule activity (TNA) per plant for treatments and cultivars in combined analysis of variance (ANOVAs) for two greenhouse studies and two exposure dates in the field; however, treatment × cultivar interactions were nonsignificant in all cases. Compared with filtered air controls, the air pollution treatment reduced TNA by an average of 16.4 and 27.4% in the greenhouse and field studies, respectively. Specific nodule activities (SNA) were unaffected by the treatments in both studies. In the greenhouse studies, the O4 and SO2 treatment lowered the chlorophyll a content by 14.1%, but no significant differences were observed in the field study. Chlorophyll b contents were unaffected by treatments in both investigations. In these studies, the sensitivity of changes in chlorophyll contents in soybean leaves following exposures to O3 and SO2 at concentrations found in the atmosphere were found to be too low to be of practical value for screening plants for tolerance to air pollutants.