For a perfect cup of tea, not only the type of tea and preparation play a role, but also the microbes that colonize the roots of the tea plant. A study now shows that microorganisms can increase the quality of tea by promoting the plant’s nitrogen absorption. When the researchers transferred microbes from the roots of particularly high-quality tea plants to other tea plants, this increased the quality of both simple and fine tea varieties. The targeted use of microbial communities could lead to new high-quality teas and also reduce the use of chemical fertilizers.
The taste of tea is influenced by numerous factors: the type of tea, the drying and fermentation of the tea leaves, storage and finally the way the tea is brewed. Even the soil in which the tea plant grows can affect its taste. For example, soils that are rich in minerals are said to produce special flavor nuances. An important indicator of tea quality is a high content of the amino acid theanine. Theanine not only provides a full taste, but is also said to have health benefits. Tea with a high theanine content is said to have a particularly relaxing effect.
Types of tea tested
A team led by Wei Xin from the Fujian University of Agriculture and Forestry in China has now investigated how the microorganisms on the roots of the tea plant affect the theanine content of the leaves and thus the quality of the tea. “Recent studies have pointed to the regulatory role of soil microbes in plant roots in nutrient uptake and metabolism,” explain the researchers. “However, how these regulatory mechanisms affect tea quality was unclear.”
As a measure of tea quality, the team looked at the theanine content in the roots and leaves of 17 different types of tea. “Theanine content is a crucial factor for tea quality and is influenced by both genetic factors and the external environment,” explain the researchers. Since the theanine content varies seasonally, they collected the samples in both spring and fall. For further analysis, they selected a type of tea with a particularly high theanine content, the high-quality Rougui tea, and a type of tea with a low theanine content, the so-called Maoxie tea. For these two varieties, they analyzed in detail which microbes colonized the roots of the plants.
Improved nitrogen absorption
“Using microbiomics, we found significant differences in microbial communities in the roots of tea plants of different quality, especially in microorganisms related to nitrogen metabolism,” reports Xin’s colleague Tongda Xu. The microorganisms on the roots of Rougui tea enabled the plant to absorb nitrogen particularly effectively. This in turn is a basic component of theanine and ensures that the sought-after amino acid is increasingly formed.
In the next step, the researchers put together a synthetic microbial community based on the microorganisms found on Rougui tea. They transferred these to the roots of various other tea plants. “Our expectation was that the synthetic microbial community obtained from the roots of high-quality tea plants would improve the quality of low-quality tea plants,” says Xin’s colleague Wenxin Tang. These expectations were exceeded: “To our amazement, we discovered that the synthetic microbial community not only improves the quality of “Inferior tea plants are improved, but also have a significant beneficial effect on certain high-quality tea varieties.”
Also for other crops?
This effect was particularly pronounced on nitrogen-poor soils. Using the model plant thale cress (Arabidopsis thaliana), the researchers also showed that the microbial community inspired by Rougui can also ensure that other plants tolerate low nitrogen levels better. Targeted use of microbes could also help reduce the need for chemical fertilizers, both in the tea industry and possibly for other crops. In further experiments, the team plans to further optimize the composition of the microbial community and test its use in field trials.
Source: Wei Xin (Fujian Agriculture and Forestry University, China) et al., Current Biology, doi: 10.1016/j.cub.2024.01.044