Ground-level Ozone Negatively Impacts Soybean Quantity and Quality

Despite national pollution reduction policies in many countries, ground-level atmospheric concentrations of ozone in the northern hemisphere have more than doubled since the Industrial Revolution, and peak values exceed theWorld Health Organization guideline value of 50 parts per billion (ppb) in many regions.Without stronger emissions controls, global background concentrations of ozone are likely to continue to increase this century. Current ozone concentrations damage both human and plant health. In plants, ozone enters the leaves through the stomata and reacts to form other reactive oxygen species, which in turn damage proteins, membranes, and cellular function. Ozone is responsible for significant reductions in crop yields, with global economic losses estimated at $14 to $26 billion. In the U.S., ozone is estimated to cost soybean growers $1.8 to $3.6 billion in lost yields per year.

The University of Illinois and the USDA Agricultural Research Service have a unique facility for studying the effects of rising ozone and carbon dioxide concentrations on crops. The Soybean Free Air Concentration Enrichment experiment enriches the concentration of ozone or carbon dioxide around a plot of soybeans without using any enclosures. The SoyFACE work began in 2001, designed to discover the effects of atmospheric change on the agronomy and productivity of midwestern crops as well as to find solutions that will help crops better adapt to this future. Current experiments include season-long warming, heat wave simulations, and drought stress treatments in addition to elevated carbon dioxide and elevated ozone concentrations.

Seed yield response

In 2009 and 2010, 18 soybean cultivars were exposed to a range of ozone concentrations, from about 40 to 115 ppb. A number of physiological and agronomic measurements were taken to characterize soybeans' response to ozone, including foliar damage scores, leaf chlorophyll content, leaf photosynthetic rates, plant height, stem diameter, canopy size, seed weight, seed oil and protein content, seed mineral content, and seed yield. The results showed that any increase in ozone above background concentrations (currently about 40 ppb) reduced yields by 0.5 bu/acre for every part per billion of ozone when averaged across cultivars. Individual seed weight, the number of pods per node, and the number of seeds per pod decreased with increasing ozone, contributing to the overall yield reduction. Yields were also reduced by a decrease in the duration of seed filling, with the highest concentration of ozone reducing duration by more than 10 days.

Effects of ozone

In addition to negative effects of ozone on seed quantity, there were significant effects on seed quality.While total oil and protein content in the seeds did not change with increasing ozone concentration, it altered the fatty acid profile of the seeds, resulting in higher levels of undesirable linoleic and linolenic acids. Linolenic acid in particular is oxidatively unstable and therefore unfavorable for food applications. In addition to creating changes in fatty acid profiles, elevated ozone increased the seed content of many elements, including aluminum, sulfur, calcium, zinc, arsenic, strontium, and cadmium. The downstream effects of these changes in oil profiles and mineral contents are not fully known, but they could impact both soybean processing and soybean growth.

In 2011, we have planted 200 soybean recombinant inbred lines at SoyFACE to investigate ozone tolerance via a genetic mapping approach. Using the latest molecular marker technology, we will generate a genome-wide linkage map, which will then be used to map quantitative trait loci (QTL) associated with foliar damage and yield loss due to ozone. This research will provide the initial framework for future efforts in breeding for ozone tolerance in soybean.

Lisa Ainsworth

Lisa Ainsworth
USDA-ARS Plant Molecular Physiologist
Professor of Plant Biology & Crop Sciences

Dr. Randy Nelson
Dr. Jeff Skoneczka
Amy Betzelberger
Courtney Leisner