Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/1995
Publication Date: N/A
Interpretive Summary: An important advantage of soybean in many cropping systems is the ability to fix atmospheric nitrogen into an organic form. Consequently, soybean does not require the application of nitrogen fertilizer which is an important cost of growing other crops and the fertilizer can have negative environmental impacts. However, to obtain high soybean yield it is necessary to maintain high nitrogen fixation rates through the growing season. Nitrogen fixation activity unfortunately decreases after only fairly small decreases in soil water content. In previous research we had discovered that the nitrogen fixation in the soybean cultivar Jackson is less sensitive to soil drying than other soybean cultivars. This paper reports the results of a number of experiments fully documenting the unique physiological and genetic characteristics of Jackson. Jackson appears to offer an important germplasm source for improving soybean yields when subjected to drying soils.
Technical Abstract: Nitrogen fixation in soybean has been shown to be sensitive to drought and it decreases at soil water deficits in advance of other physiological processes causing an important constraint on soybean performance. However, recent evidence indicates that there may be genetic variation within soybean for this trait. The cultivar Jackson was reported to have nitrogen fixation activity that was relatively drought insensitive. This study was undertaken to more fully understand this unique response. The drought tolerance of nitrogen fixation in Jackson was confirmed, as well as in one of its parents, Volstate. Interestingly, grafting studies showed that using Jackson as either the rootstock or scion conferred drought tolerance on the grafted plant. Enriching the atmosphere with oxygen around the nodules of well-watered and drought-stressed plants resulted in substantial positive responses in acetylene reduction rates in comparison to a drought sensitive line. Finally, Jackson was found to have lower levels of petiole ureides in well-watered plants than in a sensitive cultivar, and the accumulation of ureides under drought was much less in Jackson. Combined these results demonstrated that nitrogen metabolism, physiology, and genetic background are important in accounting for unique behavior of nitrogen fixation in Jackson under water-deficit conditions.