Abstract
Understanding how mangroves respond to rare cold events has implications for both restoration and conservation under climate change scenarios. This study investigated the responses of photosynthesis and activities of key enzymes involving carbon and nitrogen metabolism at different ages of Kandelia obovata to a rare cold event in the winter of 2010. This study took place on Ximen Island, Zhejiang Province, China. We measured the physiological recovery of 2–3-, 5–6-, 9–10- and 54–55-year-old K. obovata trees after freezing injury in February and March in 2011 and 2012, respectively. Chilling injury index and electrolyte leakage of K. obovata increased with increasing tree age in the winter of 2010, and electrolyte leakage in K. obovata at different ages in the winter of 2010 was far higher than that in the winter of 2011. The rare cold events significantly changed the recoveries of the leaf net photosynthetic rate (Pn) and stomatal conductance (Gs); ratios of chlorophyll a/chlorophyll b (Chl a/Chl b); contents of total soluble sugar (TSS), sucrose, free amino acid (FAA), and soluble protein; and activities of sucrose phosphate synthase (SPS), endopeptidase, and carboxypeptidase in K. obovata at different ages. These effects were mainly due to changes in the physiological mechanism in the 2-year-old trees. A clear decrease in Pn of the 2-year-old trees was observed in February 2011, as exemplified by reductions in ratios of Chl a/Chl b and chlorophyll/carotenoid (Chl/Car), as well as inhibition of the levels of TSS and FAA (osmotic substances). During recovery in 2011 and 2012, the activities of SPS and sucrose synthase (SS) were responsible for sucrose synthesis after the rare cold events in 2011, but only SPS activity was one of the main factors contributing to the metabolism of stachyose to sucrose without cold damage in 2012. Carboxypeptidase played a more important role than endopeptidase during protein hydrolysis after the rare cold events. The results suggest that the recovery of photosynthetic capacity in K. obovata was changed after a rare cold event, which is associated with pigment components and activities of SS, SPS, and carboxypeptidase, especially the seedlings.
Highlights
Understanding how mangroves respond to rare cold events has implications for both restoration and conservation under climate change scenarios
Electrolyte leakage on 31 January 2011 (T1) showed a similar pattern to the chilling injury index of K. obovata at different ages
Electrolyte leakage of the 2-year-old K. obovata was only significantly higher than that of the other ages on 31 January 2012 (T4) (P < 0.05), whereas no statistical difference was observed between the 6, 10, and 55-year-old trees
Summary
Understanding how mangroves respond to rare cold events has implications for both restoration and conservation under climate change scenarios. Mangroves are open ecosystems that straddle the land and the sea, from freshwater to seawater, providing diverse habitats for plant and animal species (Li and Less 1997) They are one of the most productive ecosystems in the world and provide a variety of ecological and societal goods and services (Liu et al 2014), such as nursing fishes (Levy et al 2015), maintaining biodiversity (Thornton and Johnstone 2015), and absorbing pollution (Debenay et al 2015). Despite their ecological relevance, mangroves that grow along the latitudinal extremes of their distribution in subtropical and tropical environments are extremely vulnerable to low temperature (Ellis et al 2006). The detailed impact of coldness on the physiology of mangroves has not been widely reported
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