Abstract: In order to investigate the response mechanism of the leaves of Impatiens hainanensis, a tropical karst specialized plant, to drought stress, eight drought treatments were set up to determine the photosynthetic, fluorescence and anatomical structures of the leaves of 6-month-old I. hainanensis seedlings. The results showed that: (1) With the intensification of drought stress, the net photosynthetic rate (Pn), transpiration rate (Tr) and stomatal conductance (Gs) showed a decreasing trend, while the interstitial CO2 concentration (Ci) showed a decreasing and then increasing trend. (2) With the intensification of drought stress, the maximum fluorescence yield (Fm), maximum photochemical efficiency (Fv/Fm) and photosynthetic performance index (PI abs) showed a decreasing trend, while the initial fluorescence yield (Fo), light energy absorbed per unit reaction center (ABS/RC), energy dissipated per unit reaction center (DIo/RC), and energy captured per unit reaction center for QA reduction (TRo/RC) showed a decreasing trend. (TRo/RC) all showed an upward trend, and drought stress suppressed the fluorescence activity. (3) With the intensification of drought stress, cell tense ratio (CTR) showed an increasing trend. The stomatal density (SD) and palisade-to-sea ratio (P/S) exhibited a general pattern of first increasing and then decreasing as stress intensified. Meanwhile, the stomatal index (SI), stomatal opening ratio (SOR), leaf thickness (LT), mesophyll tissue thickness, and spongy ratio (SR) tended to decrease. In summary, the response of I. hainanensis to different levels of drought stress varies: under mild drought conditions, drought resistance is primarily enhanced by enlarging stomatal area and stomatal density of leaf while reducing leaf thickness (most pronounced in T2 treatment). Under moderate drought conditions (T4 treatment), the palisade-to-sea ratio reaches its peak. Under severe drought conditions, drought damage is primarily mitigated by reducing the palisade-to-sea ratio and increasing cell tense ratio. The results of this study can provide a reference for the conservation of germplasm resources and population restoration of I. hainanensis.

Key words: Impatiens hainanensis, drought stress, photosynthetic characteristics, chlorophyll fluorescence, leaf anatomy

摘要： 为探究热带喀斯特专性植物海南凤仙花Impatiens hainanensis叶片对干旱胁迫的响应机制，设置8种干旱处理，测定6月龄海南凤仙花实生苗叶片的光合、荧光及解剖结构。结果表明：(1) 随着干旱胁迫加剧，净光合速率(Pn)、蒸腾速率(Tr)及气孔导度(Gs)均呈下降趋势，而胞间CO2浓度(Ci)呈先降低后升高趋势。(2) 随着干旱胁迫加剧，最大荧光产量(Fm)、最大光化学效率(Fv/Fm)及光合性能指数(PI abs)均呈下降趋势，而初始荧光产量(Fo)、单位反应中心吸收的光能(ABS/RC)、单位反应中心耗散的能量(DIo/RC)及单位反应中心捕获的用于还原QA的能量(TRo/RC)均呈上升趋势，干旱胁迫抑制荧光活性。(3) 干旱胁迫下，叶片组织结构紧密度均呈增大趋势，气孔密度和栅海比随胁迫加剧大致呈先升后降变化，而气孔指数、气孔开张比、叶片厚度、叶肉组织厚度以及组织结构疏松度均呈减小趋势。综上所述，海南凤仙花对不同程度干旱胁迫的响应方式不同：在轻度干旱处理下主要通过增大气孔面积、气孔密度，降低叶片厚度(T2处理最为明显)来提高抗旱性，在中度干旱T4处理时栅海比达到最高，重度干旱处理时主要通过降低栅海比、提高叶片组织结构紧密度来减少干旱的伤害。该研究结果可为海南凤仙花的种质资源保育、种群恢复工作提供一定参考。

关键词: 海南凤仙花, 干旱胁迫, 光合特性, 叶绿素荧光, 叶片解剖结构