Metabolomics analysis reveals the responses of tea plants to excessive calcium.

BACKGROUND: The proper growth and development of tea plants requires moderately acidic soils and relatively low calcium levels, and excessive calcium at high pH can damage tea plant roots. To reveal the effects of calcium on the responses of tea plant to three pH levels (3.5, 5.0 and 6.5), a repeated test of two factors was designed. RESULTS: Root growth and elemental analysis indicated that excessive calcium improved the growth of tea roots at low pH conditions, whereas it did not harm the growth of tea roots under normal and high pH conditions, especially at pH 6.5. Excessive calcium antagonized the absorption and utilization of magnesium by tea plants. Gas chromatography-mass spectrometry results showed that the addition of Ca2+ resulted in the primary metabolism in roots being more active at a low pH level. By contrast, it had obvious adverse effects on the accumulation of root metabolites with high calcium treatment at normal or high pH. Differential metabolites identified using ultra-performance liquid chromatography quadrupole time of flight mass spectrometry indicated that flavonoids demonstrated the largest number of changes, and their biosynthesis was partially enriched with excessive calcium at low and high pH conditions, whereas it was down-regulated under normal pH conditions. Kaempferol 3-(2'-rhamnosyl-6'-acetylgalactoside) 7-rhamnoside, quercetin 3-(6'-sinapoylsophorotrioside) and delphinidin 3-(3'-p-coumaroylglucoside) showed the greatest increase. The results of gene expression related to root growth and calcium regulation were consistent with root growth and root metabolism. CONCLUSION: The overall results demonstrated that high Ca concentrations further aggravate the detrimental effects of high pH to tea roots. However, it is interesting that excessive calcium reduced the harm of a low pH on tea root growth to some extent. © 2021 Society of Chemical Industry.

Accumulation and distribution of arsenic and cadmium by tea plants.

It is important to research the rules about accumulation and distribution of arsenic and cadmium by tea plants, which will give us some scientific ideas about how to control the contents of arsenic and cadmium in tea. In this study, by field investigation and pot trial, we found that mobility of arsenic and cadmium in tea plants was low. Most arsenic and cadmium absorbed were fixed in feeding roots and only small amount was transported to the above-ground parts. Distribution of arsenic and cadmium, based on their concentrations of unit dry matter, in tea plants grown on un-contaminated soil was in the order: feeding roots>stems approximately main roots>old leaves>young leaves. When tea plants were grown on polluted soils simulated by adding salts of these two metals, feeding roots possibly acted as a buffer and defense, and arsenic and cadmium were transported less to the above-ground parts. The concentration of cadmium in soil significantly and negatively correlated with chlorophyll content, photosynthetic rate, transpiration rate and biomass production of tea plants.

Scale and causes of lead contamination in Chinese tea.

We investigated the scale and causes of Pb contamination in Chinese tea. Lead concentrations in 1,225 tea samples collected nationally between 1999 and 2001 varied from <0.2 to 97.9 mg kg(-1) dry weight (DW), with 32% of the samples exceeding the national maximum permissible concentration (MPC) of 2.0 mg kg(-1) DW and a significant difference between tea types. There was an increasing trend in tea Pb concentration from 1989 to 2000. Proximity to highway and surface dust contamination were found to cause elevated Pb concentrations in tea leaves. Furthermore, Pb concentration in tea leaves correlated significantly and positively with soil extractable Pb, and negatively with soil pH, suggesting that root uptake of Pb from soils also contributed to Pb accumulation in tea. Potential contributions to human Pb intake from drinking tea were small at the median or national MPC Pb values, but considerable at the highest concentration found in the study.