Shining a light on crop stress - soybean 'Glow' reveals ozone Impact

A team of researchers from the USDA and the University of Illinois has unlocked a novel approach to gauge stress levels in soybean crops exposed to elevated ozone (O3). Their innovative method involves utilizing a natural phenomenon called solar-induced chlorophyll fluorescence (SIF) to assess the impact of ozone stress on soybean plants. 

During photosynthesis, soybean plants absorb sunlight, using most of the energy for their growth. Any excess energy is released as heat and a subtle glow of light, which is known as SIF. This faint natural glow can be harnessed to evaluate the efficiency of photosynthesis and determine the level of stress experienced by plants, including stress from factors like high temperatures or elevated carbon dioxide (CO2) levels. 

Genghong Wu, a former PhD student in the Department of Natural Resources and Environmental Sciences at the University of Illinois, highlighted the importance of SIF in research: "Researchers have found SIF to be a faster, safer, and non-invasive method for studying photosynthesis.  

What makes this study unique is that, for the first time, SIF was employed to measure the impact of elevated ozone stress on soybeans in their natural environment." 

In their field study, USDA ARS scientist and professor Lisa Ainsworth established a four-plot system, with four plots exposed to elevated O3 levels and four acting as control. Using a portable spectroscopic system, the research team measured SIF above the soybean canopy.  

They observed a significant decrease in SIF in the high O3 environment, with reductions of up to 36% in the late growing season. This reduction in SIF indicated that the plants were under stress due to elevated ozone levels, as other photosynthetic processes, such as electron transport and leaf-gas exchange, also decreased. 

SIF's scalability is a particularly promising aspect of this technique. Currently, it can be measured from an aircraft flying 0.6 miles above a field. Co-author Genghong Wu envisions the use of SIF from even greater distances, possibly from satellites orbiting the Earth, to monitor photosynthesis on a regional or global scale. 

Understanding how crops respond to various stresses is crucial for developing more resilient crops in the future. This innovative use of SIF offers a new tool for studying crop health and stressors, potentially leading to improved agricultural practices and crop breeding.