Comparison of physiological characteristics of Kandelia obovata at different ages in winter in the northernmost mangrove transplanted area of China

This study took place on Ximen Island within Ximen Island Marine Special Reserve, Yueqing County, Zhejiang Province, at the northernmost boundary of artificially planted mangrove plantations, to study changes in the physiological characteristics of different aged Kandelia obovata trees (aged 1, 2, 4, 8 and 53 years). Leaves and stems of different aged K. obovata were sampled in November and December (mean air temperature was 15.8 °C and 7.6 °C, respectively) for measurements of physiological traits. Results showed that from November to December, content of both chlorophyll and carotenoids, the chlorophyll a/b ratio and activity of peroxidase (POD) in leaves, the content of total soluble sugars, free amino acids, and content of K+ in the leaves and stems first increased and then decreased with increasing age. Also, Na+ content in the leaves and stems, as well as malondialdehyde (MDA) content in leaves decreased. Importantly, the measured differences in these chemicals in trees of different ages were more significant in December. We conclude that older individuals of the mangrove K. obovata were able to survive by maintaining higher levels of photosynthetic pigments and activities of antioxidant enzymes, and were able to effectively regulate ion stabilization, which promoted carbon and nitrogen metabolism. Also, disorders related to the ion balance and carbon and nitrogen metabolism may not allow K. obovata seedlings to adapt to low temperature stress. Our findings indicate that attempts to provide safe overwintering of K. obovata seedling may face significant challenges.