Variation among Soybean Cultivars in Dinitrogen Fixation Response to Drought

Abstract

AbstractDinitrogen fixation in soybean [Glycine max (L.) Merr.] is especially sensitive to soil drying, and this trait can have important negative affects on yield. An exception to this general response has been the identification of ‘Jackson’ soybean as drought tolerant for N2 fixation. The objectives of this research were to examine the response in additional soybean cultivars of N2 fixation to soil drying under field conditions, and to determine if there is any link between the drought sensitivity among cultivars and the ureide levels in the plants. Two field experiments were conducted to further examine the genetic variation in the sensitivity of soybean cultivars for biomass and N accumulation rates in response to soil drying. Substantial variation among soybean lines was found, and the drought‐tolerance trait was demonstrated again in Jackson. Differences between cultivars in the response of N accumulation to drought stress were associated with differences in petiole ureide concentration found in well‐watered plants. An experiment was conducted in the greenhouse with eight soybean cultivars grown in pots and exposed to drought by soil dehydration over a 2‐wk period. Differences among cultivars in the sensitivity of N2‐fixation rates to soil drying found from measurements of acetylene reduction activity (ARA) in the greenhouse correlated with differences in N accumulation in the field (r2 = 0.86). The tolerance of N2 fixation to drought stress was associated (r2 = 0.84) with maximum ARA in response to changes in O2 concentration around nodules. Among the eight cultivars, there was a significant negative correlation (r2 = 0.73) between the drought tolerance of N2 fixation and ureide concentration in the xylem sap. Ureide levels might be an efficient way to screen large numbers of genotypes for N2‐fixation drought tolerance.