Summary Content
Research importance: Atmoshperic drought is one of the most important environmental factors that limit soybean yields in the U.S.. While this effect is strong and quantifiable, surprisingly however, it is rarely considered in breeding and management, mainly because this stress rarely generates visual symptoms. In Minnesota, atmospheric drought typically increases more than 600% daily during the growing season, representing a regular source of stress. We have recently discovered that atmospheric drought impacts nitrogen fixation in soybean, which is the process by which they take up ‘free’ nitrogen from the atmosphere to be later invested in making seed protein. Even more importantly, we have preliminary evidence showing that some genotypes may actually ‘boost’ their nitrogen fixation in response to this stressor.
A first goal of this project was to screen a set of 24 highly diverse breeding lines to look for this trait. This is to identify superior genotypes to be used as donor parents in the U of M soybean breeding program and identify superior commercial varieties to be recommended to farmers. To this end, our lab developed a technology that measures non-invasively nitrogen fixation in response to atmospheric drought, by tracking hydrogen production by roots, under various conditions, even the field (see Figure 1). A second goal was to predict state-wide yield gain gradients and therefore profitability for Minnesota farmers resulting from such a trait.
Findings
We discovered that some promising genotypes do indeed increase their nitrogen fixation in response to atmospheric drought, rather than decreasing it. We found that this sensitivity is dependent on the growth stage, that is, some genotypes express it across the entire growing season while others do not. We also discovered that while commercial varieties do not express this favorable trait, it exists in breeding lines and undomesticated landraces. Our modeling efforts indicate significant yield gains for the Minnesota farmer if this trait is successfully introduced in varieties released to farmers. The yield increases are expected to be highest in regions that experience the highest levels of atmospheric drought, as shown on Figure 2.
Benefits for Minnesota Farmers: We conclude that there is a promising and untapped opportunity to further increase soybean yields in response to drought and therefore increase soybean farm profitability in Minnesota. Soybean breeding programs would greatly benefit from actively breeding for this trait as a new tool for developing more drought-tolerant and therefore, better yielding varieties to Minnesota farmers.
Figure 1. Illustration of the system developed by our team to measure directly and non-destructively biological nitrogen fixation in whole root system.
Figure 2. Heat map of potential Minnesota soybean yield gain gradients that would be expected if increased nitrogen fixation in response to atmospheric drought is introduced in cultivars released to farmers.
