Chlorophyll Fluorescence Characteristics of Tea Twig Cuttings in Hydroponic Environment

Purpose To study the chlorophyll fluorescence characteristics of tea twig cuttings in hydroponic environment.

Methods Using the twig cuttings of Fudingdabai tea as materials, the cuttings were first soaked in four different mass concentrations (0, 50, 100, 200 mg/L) of naphthylacetic acid (NAA) for 12 hours, and then, the cuttings were cultured by hydroponics and soil culture, respectively. The chlorophyll fluorescence parameters and growth and development indexes of tea twig cuttings cultured in different substrates under different mass concentrations of NAA were measured by PAM-2500 portable chlorophyll fluorescence analyzer and biological statistical methods.

Results In the culture of tea twig cuttings, 89.4%-96.1% of the light energy was dissipated, and only 3.9%-10.6% of the light energy was used for photosystem Ⅱ photochemical reactions. Compared with soil cultured cuttings, hydroponic cuttings showed significantly increased variable fluorescence (F_v), potential photochemical activity (F_v/F_o), photochemical quenching coefficient (qP), electron transport rate (ETR), and callus rate; while initial fluorescence (F_o) and mortality rate were significantly reduced. Compared with the hydroponic control, hydroponic cuttings soaked in 100 mg/L NAA showed a significant increase in F_v/F_o, maximum electron transfer efficiency (ETR_max), photochemical reaction Y(II), light response curve slope, and callus rate; while F_o and mortality rates were significantly reduced. Compared with the soil culture control, the soil culture cuttings soaked in 50 mg/L NAA showed a significant decrease in maximum fluorescence (F_m), F_v, primary light energy conversion efficiency (F_v/F_m), and F_v/F_o; while the rooting rate increased significantly. The rooting rate in soil culture environment was significantly higher than that in hydroponic environment, among them, the rooting rate of cuttings in the 100 and 200 mg/L NAA soaking treatment groups reaching over 30%.

Conclusion The light energy utilization efficiency of tea twig cuttings is relatively low, and strong light stress damage should be avoided. Hydroponics can obviously improve the self-protection ability of cuttings, enhance photosynthesis ability, accelerate callus formation, and different mass concentrations of NAA soaking treatment have an enhancing effect on the potential photochemical activity, light initiation rate, and callus rate of hydroponic tea twig cuttings. Among them, soaking in 100 mg/L NAA for 12 hours in the early stage of cuttings has the best effect. The results can provide a theoretical reference for the optimization of large-scale hydroponic cutting technology for tea twigs.