In 2021, the Iowa Soybean Research Center funded a three-year research project to study the effects of increased CO₂ and elevated temperatures on soybean in a climate-controlled facility known as the Enviratron located at Iowa State’s Agricultural Engineering and Agronomy (AEA) Research Farm. The project was led by ISU Professors Asheesh “Danny” Singh, agronomy; Lie Tang, agricultural and biosystems engineering; and Steve Whitham, plant pathology, entomology and microbiology.

Results from the first phase of the study provided insight into disease development and defense responses of soybean in rising CO₂ levels that, at current emission levels, will be realized within the next 35-45 years. Results were both positive and negative and in one case, the infection by the pathogen was not affected, but a greater loss in biomass was seen. The second phase of the study revealed the effect of heat stress on soybean and in changes to composition of microorganisms in the soil. 

To study the effects of increased CO₂ on soybean, soybean plants were grown in either elevated CO₂ or current levels of CO₂ in growth chambers in the Enviratron. The plants were infected with bean pod mottle virus, soybean mosaic virus, Pseudomonas syringae pathovar glycinea (bacterial blight), Fusarium virguliforme (sudden death syndrome, SDS), or Pythium sylvaticum (seedling root and stem rot). 

Results showed that the plants growing in elevated CO₂ conditions were less susceptible to bacterial blight, more susceptible to the viruses and SDS. The susceptibility to seedling root and stem rot was unchanged. Soybean defenses to bacterial blight were more strongly activated in elevated CO₂, whereas defenses against the viruses appeared to be lowered. Outcomes suggest avenues for additional research to understand why elevated CO₂ affects some diseases and to identify genes that can be used to improve soybean resistance to disease in future climates. Additional work is also needed to understand how elevated CO₂ interacts with temperature and water stresses to affect soybean diseases. 

In addition to being supported by ISRC funds, this portion of the project had leveraged funding from the ISU Plant Sciences Institute. Data and results from this project were used in support of a successful USDA NIFA grant application titled “Machine Learning-Assisted Multimodal Chemical, Biological, Physiological Sensing for Assessing Multiplex Plant Stress States.”

The second part of the research studied the effects of heat stress on soybeans, focusing on how elevated temperatures influence native soil microbial communities and their role in mitigating heat stress. A multi-omics approach was employed, which included analyzing soil microbial diversity (through bacterial and fungal sequencing), the root metabolome, gene expression, and belowground traits such as nodulation and root anatomical traits to understand how these factors collectively impact crop growth. The results revealed that elevated temperatures disrupted the composition and structure of soil microbial communities. 

Specific bacteria and fungi were strongly associated with heat stress conditions, revealing a microbial response uniquely adapted to high-temperature environments. Belowground traits, particularly nodulation and root anatomical traits, were highly sensitive to heat stress, with nodulation being significantly impaired. Elevated temperatures altered expression of genes associated with heat stress pathways. Notably, some of these responses occurred in different soybean cultivars, suggesting common mechanisms of heat adaptation in soybean. Additionally, the soil microbiome was found to play a critical role in modulating these gene expression changes under elevated temperatures. These findings reveal the complex interplay between heat stress, soil microbes, and plant physiological responses, offering valuable insights into the mechanisms of alleviating heat stress in soybeans. 

The results reveal opportunities for further research into specific molecular pathways and genes to be used to develop heat tolerant soybeans. Findings also provided evidence that soil microbes contribute to the heat stress response of soybeans and can aid in alleviating the stress. This means soil management practices may possibly be implemented to leverage microbes for improved crop health and productivity.

The final report for this project can be found on the ISRC website. In addition, Whitham was part of a group of researchers who submitted an article to New Phytologist on the elevated CO₂ portion of the project and commentary on the article was recently published in New Phytologist.