珍稀树种红花玉兰在华北地区的最适光环境

珍稀树种红花玉兰对其华南原产地的自然环境有良好的适应性, 但在华北地区却生长不良。通过对红花玉兰在华北地区一个生长季内对三种光照水平(100%、70%、40%全光照)的光合和生长响应分析, 结果表明:在70%全光照条件下, 红花玉兰幼苗的净光合速率、光饱和点、株高、基径、根生物量和茎生物量均达到最高水平。随着光照强度的减弱, 暗呼吸速率、光补偿点、比叶重量、叶片厚度和密度显著降低, 表观量子效率、最大荧光Fm、可变荧光Fv、Fm/Fo(Fo为初始荧光)、Fv/Fo、Fv/Fm、叶绿素含量、叶面积和叶柄角度均显著增大。说明70%全光照最适于一年生红花玉兰幼苗在华北地区的生长, 全光照和40%全光照条件下幼苗则因光量的过剩和不足而生长不良。因此建议将红花玉兰栽植在林缘或林窗地带, 可为这一珍稀濒危树种在华北地区的引种提供有利的适生光照环境。

Optimal Light Regime for the Rare Species Magnolia wufengensis in Northern China

The rare species Magnolia wufengensis, which is adapted to the natural conditions of its native habitat in southern China, has shown poor growth in northern regions. We analyzed the photosynthetic and growth responses of M. wufengensis grown in northern China under three light levels (100%, 70%, and 40% sunlight) during one growing season. Under 70% sunlight, plants had a maximum net photosynthetic rate (P_max), light saturation point (LSP), seedling height, basal diameter, root biomass and stem biomass. With decreasing light level, the dark respiration rate (R_d), light compensation point (LCP), specific leaf weight, leaf thickness and leaf density significantly decreased, and apparent quantum yield (AQY), maximum fluorescence (Fm), variable fluorescence (Fv), Fm/initial fluorescence (Fo), Fv/Fo, Fv/Fm, chlorophyll content, leaf area and petiole angle significantly increased. We concluded that 70% sunlight was the optimum light level for 1-year-old M. wufengensis seedlings grown in northern China. Poor growth responses were observed under full and 40% sunlight, resulting from excessive and insufficient light energy, respectively. For the successful introduction to northern China, microsites at forest edges or gaps should be favored to provide an optimal light environment for M. wufengensis.