Abstract: In order to analyze the effects of N form and weak light stress on the tea plant growth and metabolism, the two-year-old cutting seedlings of ‘Longjing 43’ were taken as experimental materials, and two different forms of N sources (NH₄⁺-N and NO₃^--N) and two light intensities (normal light and weak light) were supplied under solution culture. The results show that: (1) the net photosynthetic rate of tea seedlings was mainly affected by the N form under normal light intensity. The net photosynthetic rate of tea seedlings treated with NH₄⁺-N was significantly higher than that treated with NO₃^--N. Under the same nitrogen conditions, compared to normal light, weak light stress had a tendency to reduce the net photosynthetic rate of tea seedlings. (2) Under normal light intensity, the chlorophyll content in young shoots treated with NH₄⁺-N was significantly higher than that treated with NO₃^--N, but the chlorophyll a (Chl a)/chlorophyll b (Chl b) ratio was basically unchanged. The chlorophyll content increased significantly after weak light stress, but Chl a/b ratio under NH₄⁺-N treatment was significantly increased, while Chl a/b ratio under NO₃^--N treatment was slightly decreased. NO₃^--N treated tea plants showed better shade tolerance than that treated with NH₄⁺-N. (3) N uptake by tea seedlings was mainly influenced by both N form and light, and weak light stress helped to improve the accumulation of N in new shoots of tea seedlings. The N content of NH₄⁺-N treated tea seedlings was significantly higher than that treated with NO₃^--N under normal light. Weak light stress significantly increased the above-ground N content in tea plants. (4) Under normal light intensity, the contents of free amino acids and caffeine in young shoots treated with NH₄⁺-N were significantly higher than those treated with NO₃^--N, while the ratio of tea polyphenol to free amino acids was lower. After weak light stress, the contents of free amino acid and caffeine in shoots further increased, while the contents of tea polyphenol and the ratio of tea polyphenol to free amino acids continued to decline. The increase rate of total free amino acid and descent rate of tea polyphenol and tea polyphenol/free amino acids ratio were faster in young shoots treated with NO₃^--N than those treated with NH₄⁺-N. The composition of shoot quality was mainly affected by light intensity, but tea polyphenol-free amino acids ratio was influenced by both light intensity and N form. The research results provide theoretical basis for the analysis of its mechanism.

Key words: tea plant, ammonium nitrogen, nitrate nitrogen, light intensity, photosynthesis, quality component