Abstract:

The research was conducted to reveal the leaf anatomical structure characteristics and photosynthetic physiological response mechanism of different Toona sinensis clones under natural high temperature and drought stress, and provide reference for T. sinensis cultivation and germplasm resource utilization. Using 5 2-year-old T. sinensis clones seedling as the research objects, including ‘XC34-2’、‘XC12-10’、‘XC9-9’、‘XC18-4’、‘XC6-6’, and 2 native varieties as reference, including ‘Black oil toona’ and ‘Red oil toona’. Leaf anatomical structure, chlorophyll contents and chlorophyll fluorescence parameters characteristics under high temperature and drought stress were measured, the single factor analysis of variance were used to compare the differences between all indexes among the clones. The results showed that the middle vein of the five clones were thinner than those of ‘Black oil toona’ and ‘Red oil toona’, and other anatomical structures were thicker than those of ‘Black oil toona’ and ‘Red oil toona’, except for the spongy tissue, among which ‘XC18-4’ had the thickest leaves and the most developed palisade tissue and spongy tissue. The thickest cuticle (2.01 μm) of ‘XC34-2’ was 1.63 times that of the thinnest cuticle of ‘Red oil toona’. Seven clones subjected to the extremely different degree of photoinhibition in the same dry and hot environment, with Fv/Fm varying from 0.67 to 0.79. High temperature and drought stress affected the distribution of excitation energy absorbed by PS Ⅱ in T. sinensis clones. ‘XC34-2’ had higher Y(Ⅱ) and lower Y(NO) and Y(NPQ), and ‘Red oil toona’ was roughly the opposite. In addition, different clones took different photoprotection strategies under high temperature and drought. The excess excitation energy in ‘XC9-9’ and ‘XC18-4’ was mainly contributed by the closed PSⅡ reaction center, and the excess excitation energy shifted to regulatory energy dissipation [Y(NPQ)], while the non-regulatory energy dissipation [Y(NO)] in ‘Red oil toona’ and ‘XC6-6’ played an equally important role in the unworked energy. Four typical indicators were screened by principal component analysis, including cuticle thickness, chlorophyll a/b ratio, maximum photochemical quantum yield and palisade tissue thickness. According to the results of the average subordination function scores, the high temperature and drought tolerance of 5 T. sinensis clones was stronger than that of the two native varieties. With strong capable of dry-hot burn resistance, water regulation and absorption, transformation and utilization of light energy, ‘XC18-4’ got the highest average score of subordination function (0.929), and was classified as high resistance clone according to the 5-level scoring method, followed by ‘XC34-2’ (0.747), belonging to a resistance clone under hot and drought stress. ‘Red oil toona’ (0.219) was more sensitive to high temperature and drought stress.

Key words: Toona sinensis, natural high temperature and drought, anatomical structure, chlorophyll, fluorescence of chlorophyll