Abstract:

Objective: The aim of this study was to investigate the responses of leaf phenotype and leaf economics spectrum of Kandelia obovata under natural tidal habitat in order to examine the adaptation mechanism of K. obovata under periodic tidal inundation. Method: The leaves above and under high tide line of mature forest of K. obovata in Luoyuan Bay in Fuzhou City of Fujian Province were measured, with those above the high tide line without tidal inundation used as control group, to study phenotype characteristics of the leaves and the relationships among each leaf characteristics and the leaf economics spectrum. Result: Compared with the leaves above the high tide line, dry weight, petiole length and dry matter content of the leaves under the high tide line were significantly smaller (P < 0.01), the leaf shape index was significantly smaller (P < 0.05) and the specific leaf area was significantly larger (P < 0.01). Among the stomatal characteristics, stomatal length, width, area, circumference, aperture, opening length, opening area and opening circumference of the leaves under the high tide line were significantly larger than those of the leaves above the high tide line(P < 0.01), but the stomatal density was significantly smaller (P < 0.01). Net photosynthetic rate, transpiration rate and stomatal conductance of the leaves under the high tide line were significantly lower, while the CO₂ concentration was significantly higher (P < 0.01). Carboxylation rate of the leaves under the high tide line was significantly smaller (P < 0.01), and water use efficiency was not significantly different between the leaves above and under the high tide line. The correlation between the stomatal characteristics and the photosynthetic function of the leaves above the high tide line was higher than that of the leaves under the high tide line, while the correlation between the stomatal characteristics and the foliar morphological traits of the leaves under the high tide line was higher than that of the leaves above the high tide line. Conclusion: Our results demonstrated that the phenotypic difference between the leaves above and under the high tide line was obvious, and the stomatal function of the leaves under the high tide line had strong adaptability, but the photosynthetic function was limited. The stomatal characteristics and the photosynthetical function of the leaves above the high tide line showed synergistic evolution, while the stomatal characteristics and the foliar morphological traits of the leaves under the high tide line indicated adaptive convergence. In order to adapt to the natural tidal habitat, there were obvious survival strategies in the leaves above and under the high tide line of Kandelia obovata. The results of the leaf economics spectrum indicated that the leaves under the high tide line generally shifted toward the "slow investment-return" end, with smaller dry matter content and stomatal density, lower net photosynthetic rate and larger specific leaf area, stomatal area and stomatal opening, so as to adapt to the extreme tidal inundation environment of low light and hypoxia. The leaves above the high tide line shifted toward the "fast investment-return" end to cope with special habitats such as strong winds and waves.

Key words: Kandelia obovata, tidal inundation, leaf phenotype, leaf economics spectrum