Root microbes may be the secret to a better-tasting cup of tea

Tea aficionados would do anything to find a variety that makes a tastier cup.

China is a country obsessed with the drink and all of its facets – from cultivation, brewing, and serving techniques to methods of consumption and the tea ceremony that have significantly influenced the country throughout history. Now Chinese experts have found that the type of microbes living off the tea roots make all the difference.

A study entitled “Root microbiota of tea plants regulate nitrogen homeostasis and theanine synthesis to influence tea quality,” which has just appeared in the journal Current Biology by scientists at Fujian Agriculture and Forestry University, shows that the making of a delicious cup of tea depends on another key ingredient: the collection of microbes found on the part of the plant that’s underground. By changing that collection, the authors showed that they could make good-quality tea even better.

“Significant disparities in microbial communities, particularly nitrogen metabolism-related microorganisms, were identified in the roots of tea plants with varying qualities through microbiomics,” said researcher Tongda Xu. “Crucially, through the isolation and assembly of a synthetic microbial community from high-quality tea plant roots, we managed to notably enhance the amino acid content in various tea plant varieties, resulting in an improvement in tea quality.”

China boasts of a wealth of genetic resources for growing tea plants, but the researchers explain that improving the quality of tea through molecular genetic breeding methods is challenging. There’s interest in finding other ways to modify and enhance tea, perhaps including the use of microbial agents. Earlier studies showed that soil microbes living in plant roots affect the way nutrients are taken up and used within plants. In the new study, the researchers wanted to learn more about specifically how root microbes affect tea quality.

Research findings 

They found that the microbes in tea roots affected their uptake of ammonia that, in turn, influenced the production of theanine, which is vital for determining a tea’s taste. They also saw variations in the microbes colonizing different teas. By comparing tea varieties with different amounts of theanine, they identified a set of microbes that looks promising for altering nitrogen metabolism and boosting theanine levels.

They next built a synthetic microbial community that they called SynCom, which closely mirrored the one found in association with a high-theanine tea variety called Rougui. When they applied SynCom to tea roots, they found it boosted theanine levels. The microbes also allowed Arabidopsis thaliana, a plant commonly used in basic biological studies, to better tolerate low nitrogen conditions.

“The initial expectation for the synthetic microbial community derived from high-quality tea plant roots was to enhance the quality of low-quality tea plants,” said study co-author Wenxin Tang. “However, to our astonishment, we discovered that the synthetic microbial community not only [did this,] but also exerts a significant promoting effect on certain high-quality tea varieties. Furthermore, this effect is particularly pronounced in low-nitrogen soil conditions.”

The findings suggest that synthetically produced microbial communities could improve teas, especially when grown in nitrogen-deficient soil conditions, they say. Because tea trees need lots of nitrogen, the discovery could help to improve their quality while reducing the use of chemical fertilizers. The findings may also have important implications for agricultural crops more broadly.

“Based on our current experimental findings, the inclusion of the SynCom21 microbial community has not only improved the absorption of ammonium nitrogen in different tea varieties but also enhanced the uptake of ammonium nitrogen in Arabidopsis thaliana,” Xu explained. “Our study provides compelling evidence supporting the use of root microorganisms as functional microbial fertilizers to enhance tea quality. This suggests that the ammonium nitrogen uptake-promoting function of SynCom21 may be applicable to various plants, including other crops.”

For instance, it could allow for growing rice with improved qualities including greater protein content, the team suggested.  They now plan to further optimize SynCom and assess its use in field trials. They also hope to learn more about how root microbes affect other secondary metabolites in tea trees.