Improving Tea Quality by Balancing ROS and Antioxidant System through Appropriate Ammonium Nitrogen Application

Nitrogen is an important nutrient for the tea plant ( Camellia sinensis ), which profoundly affects the quality and value of tea. In this study, the variations of biochemical activities, antioxidant systems, and tea quality of two tea varieties under four levels of nitrogen fertilizers were analyzed to explore the responses of tea plants to nitrogen stress. The primary maximum photochemical efficiency of PSII( F v / F m ), the photochemical quenching coefficient ( qP ) and the relative electron transport rate ( rETR ) decreased under nitrogen deficiency (ND) and high nitrogen treatments (HN) in tea plant. Meanwhile, the levels of reactive oxygen species (ROS) increased significantly under ND/HN treatments, and the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) increased under HN/ND treatments. The relative expressions of antioxidant biosynthesis enzyme genes ( CsSOD , CsPOD , CsCAT and CsAPX ) were up-regulated under ND/HN treatments. Furthermore, the change trend of total free amino acid content under ND/HN treatments showed that nitrogen stress was not conducive to the accumulation of free amino acid content in tea, which may be related to the increase in ROS. This study presents a potential approach to improve tea quality by balancing ROS and antioxidant systems.