Pelozo Andressa, Boeger Maria Regina T, Sereneski-de-Lima Carolina, Soffiatti Patricia
Rev Biol Trop. 2016 Mar;64(1):305-17. doi: 10.15517/rbt.v64i1.17923.
The initial phase of a plant life cycle is a short and critical period, when individuals are more vulnerable to environmental factors. The morphological and anatomical study of seedlings and saplings leaf type enables the understanding of species strategies of fundamental importance in their establishment and survival. The objective of this study was to analyze the structure of seedlings and saplings leaf types of three mangrove species, Avicennia schaueriana, Laguncularia racemosa, Rhizophora mangle, to understand their early life adaptive strategies to the environment. A total of 30 fully expanded cotyledons (A. schaueriana and L. racemosa), 30 leaves of seedlings, and 30 leaves of saplings of each species were collected from a mangrove area in Guaratuba Bay, Paraná State, Brazil. Following standard methods, samples were prepared for morphological (leaf dry mass, density, thickness) and anatomical analysis (epidermis and sub-epidermal layers, stomata types, density of salt secretion glands, palisade and spongy parenchyma thickness). To compare leaf types among species one-way ANOVA and Principal Component Analysis were used, while Cluster Analysis evaluated differences between the species. We observed significant structural differences among species leaf types. A. schaueriana showed the thickest cotyledons, while L. racemosa presented a dorsiventral structure. Higher values of the specific leaf area were observed for seedlings leaves of A. schaueriana, cotyledons of L. racemosa and saplings leaves of A. schaueriana and R. mangle. Leaf density was similar to cotyledons and seedlings leaves in A. schaueriana and L. racemosa, while R. mangle had seedlings leaves denser than saplings. A. schaueriana and R. mangle showed hypostomatic leaves, while L. racemosa amphistomatic; besides, A. chaueriana showed diacytic stomata, while L. racemosa anomocytic, and R. mangle ciclocytic. Seedling leaves were thicker in R. mangle (535 μm) and L. racemosa (520 μm) than in A. schaueriana (470.3 μm); while saplings leaves were thicker in L. racemosa (568.3 μm) than in A. schaueriana seedlings (512.4 μm) and R. mangle (514.6 μm). Besides, seedlings leaves palisade parenchyma showed increasing thickness in L. racemosa (119.2 μm) < A. schaueriana (155.5 μm) < R. mangle (175.4 μm); while in saplings leaves as follows R. mangle (128.4 μm) < A. schaueriana (183.4 μm) < L. racemosa (193.9 μm). Similarly, seedlings leaves spongy parenchyma thickness values were as follows A. schaueriana (182.6 μm) = R. mangle (192.8 μm) < L. racemosa (354.4 μm); while in saplings were A. schaueriana (182.6 μm) = R. mangle (187.3 μm) < L. racemosa (331.3 μm). The analyzed traits, in different combinations, represent morphological adjustments of leaf types to reduce water loss, eliminate salt excess, increase the absorption of light, allowing a higher efficiency on the maintenance of physiological processes in this initial growth stage.
植物生命周期的初始阶段是一个短暂而关键的时期，在此期间个体更容易受到环境因素的影响。对幼苗和幼树叶片类型进行形态学和解剖学研究，有助于理解物种在其建立和生存过程中至关重要的策略。本研究的目的是分析三种红树植物——肖氏海榄雌（Avicennia schaueriana）、总状拉贡木（Laguncularia racemosa）、红树（Rhizophora mangle）——的幼苗和幼树叶片类型结构，以了解它们在早期生活中对环境的适应策略。从巴西巴拉那州瓜拉图巴湾的一个红树林地区采集了每个物种的30片完全展开的子叶（肖氏海榄雌和总状拉贡木）、30片幼苗叶片和30片幼树叶片。按照标准方法，制备样本用于形态学（叶片干质量、密度、厚度）和解剖学分析（表皮和亚表皮层、气孔类型、盐分分泌腺密度、栅栏组织和海绵组织厚度）。为了比较物种间的叶片类型，使用了单因素方差分析和主成分分析，而聚类分析评估了物种之间的差异。我们观察到物种叶片类型之间存在显著的结构差异。肖氏海榄雌的子叶最厚，而总状拉贡木呈现背腹结构。肖氏海榄雌的幼苗叶片、总状拉贡木的子叶以及肖氏海榄雌和红树的幼树叶片的比叶面积值较高。肖氏海榄雌和总状拉贡木的子叶和幼苗叶片的叶密度相似，而红树的幼苗叶片比幼树叶片密度大。肖氏海榄雌和红树的叶片为下气孔型，而总状拉贡木为双面气孔型；此外，肖氏海榄雌的气孔为双细胞型，总状拉贡木为不规则型，红树为环列型。红树（535μm）和总状拉贡木（520μm）的幼苗叶片比肖氏海榄雌（470.3μm）的厚；而总状拉贡木（568.3μm）的幼树叶片比肖氏海榄雌幼苗（512.4μm）和红树（514.6μm）的厚。此外，幼苗叶片的栅栏组织厚度在总状拉贡木（119.2μm）<肖氏海榄雌（155.5μm）<红树（175.4μm）之间逐渐增加；而幼树叶片的情况如下：红树（128.4μm）<肖氏海榄雌（183.4μm）<总状拉贡木（193.9μm）。同样，幼苗叶片的海绵组织厚度值如下：肖氏海榄雌（182.6μm）=红树（192.8μm）<总状拉贡木（354.4μm）；而在幼树中为：肖氏海榄雌（182.6μm）=红树（187.3μm）<总状拉贡木（331.3μm）。所分析的性状以不同组合形式，代表了叶片类型的形态调整，以减少水分流失、消除盐分过量、增加光吸收，从而在这个初始生长阶段更高效地维持生理过程。
