Influences of water depth gradient on photosynthetic fluorescence characteristics of <i>Vallisneria natans</i>

Abstract

为研究水深梯度对苦草(Vallisneria natans)光合荧光特性的影响,实验设置0.6、1.3、2.0m 3个水深条件,利用水下饱和脉冲荧光仪测定3种水深处理下苦草叶片的荧光参数和快速光响应曲线.结果表明:(1) 随着水深增加,无性系分株数、叶片数、根系总长度、根系表面积等形态指标显著降低,而最大叶长、平均叶长、最大叶宽没有显著变化,2.0m处苦草生长受到抑制;(2) 不同水深对苦草叶片初始荧光F₀和最大荧光F_m没有显著影响,而最大量子产率F_v/F_m和荧光参数F_v/F₀随着水深增加显著增加,叶片光合系统Ⅱ光化学效率亦显著提高;(3) 0.6m处苦草的相对电子传递速率显著低于2.0m处;(4) 通过拟合光响应曲线所得的光响应曲线初始斜率、光抑制参数、最大电子传递速率以及半饱和光强在不同的水深处理间均差异显著;(5) 2.0m处苦草叶片的叶绿素a(Chl.a)、叶绿素b(Chl.b)、类胡萝卜素(Car)以及Chl.a+Chl.b含量均显著高于0.6m处,而Chl.a/Chl.b和Car/Chl.a的差异则不显著.综上所述,0.6m处苦草的光合能力较弱、保护机制强,而2.0m则相反,从而说明苦草通过调节自身光合生理来适应不同水深环境.;In order to study the influences of water depth gradients on photosynthetic fluorescence characteristics of Vallisneria natans, three water depths of 0.6, 1.3 and 2.0 m were set, and Chlorophyll fluorescence characters and rapid light curves (RLCs) of V. natans grew in three water depth treatments were measured by a submersible, pulse-amplitude modulated fluorescence: Diving-PAM. The results suggested that, with water depth increasing, the number of ramets and leaves, total root length, root surface area decreased significantly, while the maximum leaf length, average leaf length, maximum leaf width did not change significantly. The growth of V. natans under 2.0 m were restricted. With the increase of water depth from 0.6 m to 2.0 m, the difference of minimum fluorescence (F₀) and maximum fluorescence (F_m) were not significant, while maximum quantum yield of photosystemⅡ(PSⅡ) and fluorescence parameter F_v/F₀ increased significantly, which indicated that photochemical efficiency of PSⅡof V. natans grew under the condition of 2.0 m was improved remarkably. The photosynthetic efficiency in leaf of V. natans grew in water depth of 2.0 m with lower light intensity was higher than that grew in water depth of 0.6 m with higher light intensity, and V. natans grew in water depth of 0.6 m had better light protection mechanisms via fluorescence quenching assay. Compared to the leaf of V. natans grew under the condition of 0.6 m, the leaf grew in water depth of 2.0 mgot higher relative electron transport rate, and the initial slope of RLCs, light suppression parameter, maximum electron transport rate and minimum saturating irradiance were significantly different. The contents of chlorophyll-a (Chl.a), chlorophyll-b (Chl.b), carotenoid (Car) of the leaf of V. natans grew in water depth of 2.0 m were significantly higher than those grew in water depth of 0.6 m, but the ratio of Chl.a and Chl.b, the ratio of Car and Chl.a were not significantly different. The experimental results above reveal that with the increase of the water depth from 0.6 m to 2.0 m, the photosynthetic capability of V. natans became weaker, however, the light protection mechanisms of the V. natans showed the reverse, indicating that V. natans was likely to adapt to different environment caused by water depths by adjusting itself photosynthetic physiology.