Increased warming, ozone have harmful effects on plant roots

Soy plants may appear healthy, but the roots suffer from warmer temperatures and increased ozone levels. Photo courtesy NC State University.

Two factors that play key roles in climate change – increased global warming and increased ozone levels – appear to have deleterious effects on the roots of soybean plants, their relationship with symbiotic microorganisms in the soil, and the way the plants store carbon.

The results, published in the July 9th issue of Science Advances, show little changes to aerial plant shoots, but some worrying results underground, including increased inability to hold carbon, which is instead released into the atmosphere as a greenhouse gas will.

North Carolina State University (NC State) researchers studied the interplay of warming and elevated ozone levels with certain key underground organisms – arbuscular mycorrhizal fungi (AMF) – that promote chemical interactions that hold carbon in the soil by preventing soil organic matter from decomposing. thereby stopping the escape of carbon from the decomposing material.

“The ability to fix carbon is very important to soil productivity – in addition to the harmful effects of increasing greenhouse gases when that carbon escapes,” said Shuijin Hu, professor of plant pathology at NC State and corresponding author of the paper.

AMF is present in the roots of approximately 80% of plants growing on land and is a win-win relationship with plants. AMFs take up carbon from plants and provide nitrogen and other beneficial soil nutrients that plants need to grow and develop.

In the study, the researchers created plots of soybeans with elevated air temperatures of around 3 degrees Celsius, plots with higher ozone levels, plots with higher warming and ozone levels, and control plots with no changes. The resulting experiments showed that warming and increased ozone levels make soybean roots thinner as they save resources to get the nutrients they need.

Soybean varieties are often sensitive to ozone, Hu said. Ozone levels have been reasonably stable or even declining in some parts of the United States over the past decade, but have increased dramatically in areas of rapid industrialization such as India and China.

“Ozone and warming have been shown to be very stressful for many plants – not just soybeans – and many grasses and tree species,” Hu said. “Ozone and warming make the plants weak. Plants try to maximize nutrient uptake so that their roots get thinner and longer as they need to use the sufficient volume of soil for resources. This weakness leads to a decrease in AMF and a faster turnover of the root and fungal hyphae, which stimulates decomposition and makes carbon sequestration difficult. These cascading events can have profound effects underground, although in some cases the plant shoots appear normal. “

Hu said he was surprised that the exposure to warming and ozone did not affect plant shoots much; the biomass of the plant leaves in both control and test plots was approximately the same.

Perhaps more surprisingly, Hu said that more warming and ozone changed the type of AMF that soybean crops colonize.

The study showed that concentrations of a species of AMF called Glomus decreased with increasing warming and ozone, while those of a species called Paraglomus increased.

“Glomus protects organic carbon from microbial degradation, while Paraglomus absorbs nutrients more efficiently,” said Hu. “We didn’t expect these communities to change this way.”

Hu plans to further investigate the systems around carbon sequestration in the soil as well as other greenhouse gas emissions from the soil, such as nitrous oxide or N2O.

The study was funded by the U.S. Department of Agriculture-National Institute of Food and Agriculture (awards 2012-02978-230561 and 2018-51106-28773); the USDA-Agricultural Research Service and NC State’s College of Agriculture and Life Sciences. H. David Shew and Richard Zobel co-authored the paper, as did Kent Burkey, who works at NC State and the USDA’s Agricultural Research Service. Burkey and Zobel designed the long-term experiment on field temperature and ozone manipulation. The paper’s first author is a former NC State Ph.D. Disciple of Yunpeng Qiu.

Source: NC State

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