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K+S KALI GmbH and the Institute for Plant Nutrition and Soil Science of the University Kiel, Germany, jointly initiated a research project focussing on the impact of nutrient supply on nutrient uptake, nutrient physiology and yield formation of green tea. In addition to a basic understanding of the impact of the form of N and K supplied and the substrate pH, particular emphasise was on physiological changes underlying consequences for green tea quality. This project has generated several publications, of which the first one is summarised in the following:

Effect of alternative anions (Cl– vs. SO₄^2-) on concentrations of free amino acids in young tea plants

J. Ruan, J. Gerendás, R. Haerdter, B. Sattelmacher

Summary

The quality of green tea is highly dependent on the concentration of free amino acids, whose profile is dominated by the unique amino acid theanine (N₅-ethyl-glutamine). A high quality is associated with a high amino acid–to–catechin ratio, but previous results indicated that excessive chloride (Cl^-) supply is detrimental for amino acid accumulation. Several experiments were conducted to investigate the effect of chloride on growth and concentrations of free amino acids in young tea plants. Soil-grown tea plants supplied with different levels of potassium (K) as K₂SO₄ or KCl exhibited increased concentrations of free amino acid in young shoots only when supplied with K₂SO₄, and the negative effect of KCl supply was mainly due to a reduced concentration of theanine. Concentrations of other nutrients in plant tissues were not influenced. The uptake of Cl^- and its interaction with nitrogen (N) uptake were further investigated in a second experiment, in which soil-cultivated tea plants were supplied with varying amounts of Cl^-. Chloride application reduced yield of young shoots, and severity of leaf damage was related to the concentration of Cl^- in leaves. Nitrogen uptake was reduced by Cl- addition. To verify whether the decrease of free amino acids was simply a result of inhibited NO₃- assimilation, a third experiment was conducted, in which tea plants were NH₄⁺-fed in the absence or presence (equivalent to the NH₄⁺ concentration) of Cl^-. Again, concentrations of theanine and total free amino acids in young shoots were reduced by Cl- supply, but changes of the free-amino acid pool did not contribute to the maintenance of charge balance. However, concentration of theanine in roots, where it is synthesized, was not influenced by Cl^-. Total N concentrations of roots and mature leaves, uptake rate of NH₄⁺, and activity of glutamine synthetase in fibrous roots and young leaves were all unaffected by Cl^- as well. It is suggested that translocation of theanine from root to shoot and its catabolism in young shoots might be influenced by Cl^-.

J. Plant Nutr. Soil Sci. 2007, 170, 49–58

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