Introduction: Mangroves that grow at the latitudinal extremes of their distribution are susceptible to extreme cold events. Successive enhancement of low temperature stress (seLTS) is a typical characteristic of extreme cold events. Low temperature stress can inhibit mangrove photosynthesis, which often inhibits the growth and development of mangroves. However, the possible reasons for impairment to photosynthesis of mangroves due to extreme cold events remain unclear. Methods: Kandelia obovata seedlings in a growth chamber were exposed to 5°C/−2°C (day/night) for 36 h (−2°C for 16 h) with 12 h light per day at 600 μmol m −2 s −1 photosynthetic photon flux density (PPFD) (a low temperature stress, aLTS), then the plants were transferred to the control condition (15°C/10°C (day/night) and allowed to recover for 5 days (R1). The other seedlings were subjected to low temperature treatment with a day/night temperature of 5°C/−1°C in a growth chamber for 24 h. Then these plants were transferred to 5°C/−2°C (day/night) under the same light and climate conditions for 36 h (two low temperature stresses, tLTS). Following the successive enhancement of low temperature treatment, these plants were returned to 15°C/10°C (day/night) for another 5-day recovery period (R2).

No abstract

Introduction: 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. Methods: 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. Results: 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.

Following publication of the original article (Zheng et al. 2016) it was brought to our attention that there was a typographical mistake in figure 6c, whereby the ordinate title had an "e" between the words "Endopeptidase" and "activity". Please see below for the corrected figure: This has now been updated on the BioMed central website.