Soy modelling tracks ozone damage

An improved modelling system can more accurately help predict the impact of ozone on soybean production.

The modelling has been developed by researchers at the University of Exeter in the United Kingdom. It was initiated because surface ozone (O3), as a pollutant, can reduce the rate of photosynthesis, limit yields, and limit the rate of crop production.

According to Soy Canada, soybean production is the third largest field crop in Canada in terms of farm cash receipts.

But the impact of surface ozone could seriously influence production levels. Past studies in the United States have shown that a normal ozone level of 10 ppmh can reduce soybean yield by 10 percent but extreme ozone levels during highly polluted days could lead to production falling to less than half the amount compared to soybeans grown in unpolluted air.

According to Soya UK, non-GM soybean has been grown in southern England and southern Wales since 1998 and varieties have been bred for early maturity, ease of harvest, higher yield, disease resistance, and adaptation to U.K. latitudes. But like all soybean crops it is vulnerable to ozone pollution.

“I read a paper by Lisa Ainsworth (molecular biologist at the United States Department of Agriculture Agricultural Research Service) who is an expert in researching ozone impact on crops and it surprised me to find out that ozone could have such a large impact on soy,” said Felix Yeung with the University of Exeter. “As soybean is one of the most important staple crops and the primary source of protein in human diet (as well as a major source for cattle feed), I wanted to research this more and see how it could affect food security.”

Ozone is a secondary pollutant created by the photochemical reaction from carbon monoxide as well as volatile organic compounds (VOC). Climate plays an important role in ozone production due to higher radiation and warmer temperatures. Compounding the problem are stagnant air masses which trap pollutants and create high ozone levels that threaten all those with respiratory issues.

Yeung said that ozone damages almost all living things depending on their sensitivity. It is visible on the leaves of broadleaf trees and especially fast-growing plants with thin leaves.

Since most crops are fast growing and soy crops have a relatively large leaf area, soybean is particularly sensitive to ozone.

Ozone entering the stomata of leaves can create reactive oxygen species (ROS), an unstable molecule that reacts with other molecules in a cell and can damage DNA, RNA, proteins and possibly cause cell death. Leung said it can oxidize proteins such as rubisco which is essential for photosynthesis. An affected leaf would show red mottles and eventually wilt. The reduced photosynthesis will ultimately reduce crop yield.

“Currently, ozone concentrations are projected to increase globally, which could have a significant impact on agriculture and food security,” said Leung. “Economic loss from ozone damage is already estimated at US$14 billion to $26 billion.”

The impact of ozone on soybean production can now be predicted more accurately because of improvements to a climate-vegetation computer modelling system called JULES —Joint U.K. Land Environment Simulator. It was developed by the Meteorological Office and the U.K. Centre for Ecology and Hydrology located at Lancaster University.

“Scientists use this model to research climate-ecosystem feedback and estimate the impact of future climate change, land-use change, and emission regimes on ecosystem production,” said Leung. “The newly calibrated version of JULES will be applied regionally and globally in future JULES simulations.”

The model is driven by meteorological inputs and Leung said it assumes an ideal farm management practice with fertile soil and no pest infestation. As a result, the model has a “yield gap” that does not yet fully represent the actual farmer’s yield. Currently, the model is used for research purposes only to inform policymakers.

“In the future, when the model includes factors such as insect damage, plant diseases, etc., it will be able to close the yield gap and be able to inform farmers about expected yield more confidently.”

According to the published report, the JULES land surface model currently includes a representation of global crops (JULES-crop) but does not have crop-specific O3 damage parameters.

“This study helps to build a state-of-the-art impact assessment model and contribute to a more complete understanding of the impacts of climate change on food production,” said Leung.

Physiological parameters for ozone damage in soybean in the new model were calibrated against leaf gas exchange measurements from the Soybean Free Air Concentration Enrichment (SoyFACE) experiment at the University of Illinois.

SoyFACE is a facility for growing crops under production field conditions in at atmosphere with higher levels of carbon dioxide, ozone, temperature and altered soil/water availability. It was developed to learn about atmospheric change on the agronomy and productivity of Midwestern crops.

Other soybean observations included crop height, leaf carbon and weather data from FLUXNET sites near Mead, Nebraska.

FLUXNET is a vast global network of more than 800 micrometeorological measurement sites and sensors that use a scientific system to measure the fluctuations of vertical wind velocity and directly measure the carbon dioxide, water vapor, and heat flux in plant communities and the atmosphere. With the data, scientists can quantify the fluxes of trace gases between the land and the atmosphere.

“The agricultural community breeds crop varieties that are fast growing and with higher yield,” said Leung. “Most of the cultivar development is done by farmers, (breeders), and crop scientists in greenhouses or laboratories that are not exposed to ozone and therefore they unintentionally breed cultivars that are sensitive to ozone. We need to find some wild varieties of crop that contain the gene that is ozone resistant and try to breed modern cultivars that could balance crop yield and ozone sensitivity.”

Leung has partnered with the National Laboratory of Agrobiotechnology at the Chinese University of Hong Kong to investigate the impact of ambient ozone on bean cultivars with different ozone sensitivities. Hong Kong experiences severe air pollution with surface ozone of particular concern. The sensitive genotype bean plants produced 30 percent more flowers than the resistant genotypes as a result of stress-induced flowering caused by ozone. However, the resistant genotype had a higher success rate (17 percent) of fruiting from flowering to bean formation and fewer dead pods than sensitive varieties. Leung said that the research outcome would help improve the variables in JULES-crop studies.

The research was published in Geoscientific Model Development.

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