Growth and physiological responses of saplings of two mangrove species to intertidal elevation

Differences in growth and physiological characteristics of saplings of Avicennia marina and Kandelia obovata were compared among 3 intertidal elevations. Growth performance of A. marina generally followed the order of the middle > lower > upper elevation. At the middle elevation, A. marina had maximum values of tree height, branch number, crown length and diameter, shoot biomass and shoot to root biomass ratio (S:R). Differently, K. obovata exhibited best growth at the upper elevation, followed by the middle and lower elevation. Except for shoot biomass and S: R, all growth parameters of K. obovata showed a tendency to decline continuously with decreasing elevation. These different responses between the 2 species indicated that A. marina is more tolerant to low elevation than K. obovata. Decreasing elevation did not compromise gas exchange of A. marina leaves, while net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2 concentration of K. obovata leaves declined sharply as the elevation decreased. Leaf chlorophyll (chl) a:b ratio and contents of chl a, total chl and total carotenoid showed no significant differences among elevations for both species. With decreasing elevation, activities of superoxide dismutase and peroxidase increased significantly for both species, while significant increase in malonaldehyde contents was only recorded for K. obovata. With decreasing elevation, proline accumulation in leaves was accelerated for A. marina but not for K. obovata. These physiological responses also confirmed that A. marina is more tolerant to low intertidal elevation than K. obovata.

在3个潮间带高程之间比较了白骨壤（Avicennia marina）和秋茄（Kandelia obovata）幼苗生长和生理特性的差异。白骨壤的生长表现一般遵循中高程＞低高程＞高高程的顺序。在中高程处，白骨壤的树高、分支数、冠长和冠径、枝条生物量以及枝根生物量比（S:R）均达到最大值。不同的是，秋茄在高高程表现出最佳生长，其次是中高程和低高程。除枝条生物量和S:R外，秋茄的所有生长参数都呈现出随高程降低而持续下降的趋势。这两个物种之间的这些不同反应表明白骨壤比秋茄更能耐受低高程环境。高程降低并没有损害白骨壤叶片的气体交换，而秋茄叶片的净光合速率、蒸腾速率、气孔导度和胞间二氧化碳浓度随着高程降低急剧下降。两种植物叶片的叶绿素（chl）a:b比值以及叶绿素a含量、总叶绿素含量和总类胡萝卜素含量在不同高程之间均无显著差异。随着高程降低，两种植物的超氧化物歧化酶和过氧化物酶活性均显著增加，而丙二醛含量仅在秋茄中有显著增加。随着高程降低，白骨壤叶片中脯氨酸积累加速，但秋茄叶片中没有这种现象。这些生理反应也证实白骨壤比秋茄更能耐受低潮间带高程。