Deficit Irrigation Impact on Photosynthesis and Non-Structural Carbon Compounds in the Leaves of Tea Plants.

Tieguanyin tea plants (Camellia sinensis (L.) O. Kuntze) are commonly grown at high elevation for good quality of tea product. Scarce water supplies in this area require optimization of irrigation manage￾ment to improve water use efficiency. Greenhouse and field experiments were conducted to investigate the responses of Tieguanyin tea plants to deficit (DI) and severe deficit irrigation (SDI) by physiological methods, while full (FI) and non-irrigation (NI) were used as control. Tea plants in DI field maintained moderate water stress at −2.0 to −2.5 MPa leaf water potential, while water stress in SDI became increasingly severe. DI showed similar effect on tea leaf fresh and dry weight production with FI but increased the content of theanine. SDI and NI, however, caused a higher level of reducing sugar in tea leaves over time, sucrose and fructose content at the last stage, which was associated with an inhibition in net pho￾tosynthesis (Pn). Compared to DI, the expressing abundances of RuBisCo and GAPDH were inhibited in SDI plants at last stage, providing a molecular basis for the biochemical changes in reduced Pn due to severe water stress. Meanwhile, SDI enhanced the expressing abundance of ELIP, in turns increased leaf chlorophyll a/b (chl a/b) ratio, which showed a significantly negative relationship with photochemical quenching (qP)(r2 = 0.62) and significantly positive relationship with non-photochemical quenching (qN) (r2 = 0.78). This implied that leaf chl a/b ratio might serve as an indicator of water stress in Tieguanyin tea plants. In conclusion, a well-designed DI regime caused minimum stress to tea plant, but achieved the tea products with improved quality by saving water.