Recovery of photosynthesis, sucrose metabolism, and proteolytic enzymes in Kandelia obovata from rare cold events in the northernmost mangrove, China

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.

Mechanisms on inhibition of photosynthesis in Kandelia obovata due to extreme cold events under climate change

“…After a rare cold event in winter of 2010, the recovery of photosynthetic capacity in K. obovata seedlings in the northern limit of introduced mangroves in China is difficult during a short period (Zheng et al 2016). In the present study, P n rapidly decreased after low temperature stress treatments, particularly tLTS treatment.…”

“…The seedlings of K. obovata were therefore protected by warmer seawater. But seedlings were exposed to freezing temperature (−2.0°C) for about 16 h in 72 h. That is, there was a rare cold event in 2011, resulting in badly damaged mangroves (Zheng et al 2016). To simulate this cold event, an experiment was performed as follows: The seedlings were maintained at 15°C/10°C day/night (near minimum monthly mean temperature in Wenzhou) with 12 h light per day at 600 μmol m −2 s −1 PPFD for 15 days.…”

Genome-Wide Identification of WRKY Genes and Their Responses to Chilling Stress in Kandelia obovata

“…However, climate change has led to the expansion of various mangrove species to higher latitudes ( Osland et al, 2013 ), and K. obovata was successfully introduced to Zhoushan (29° 30′ N), Zhejiang Province, in 2016. A successive freezing spell (minimum −3.2°C) occurred in the winter of 2010 on Ximen Island (28° 25′ N), Yueqing, Zhejiang Province, China, and the leaves of K. obovata had become brown and wilted, and a high mortality of 2-year-old seedlings was reported ( Zheng et al, 2016 ).…”

Ecophysiological Analysis of Mangrove Seedlings Kandelia obovata Exposed to Natural Low Temperature at Near 30°N

“…K. obovata from Jiulong River (24 • 23 N) could grow to 7.9 m, and those from Minami-Izu, Japan (34 • 38 N) could be up to 3-4 m [35]. One of the most important factors limiting mangrove growth is the low-temperature environment, which inhibits the synthesis of chlorophyll [36]. The synthesis of chl.…”