Photosynthetic responses to submergence in mangrove seedlings

Abstract

Flooding and salinity fluctuations are common in mangrove systems. Sometimes these events are long-lasting, persisting several months. With an increased frequency of heavy rainfalls and terrestrial run-off, subsequent floods have been associated with massive mangrove mortality and failure to regenerate in the region. Owing to climate change, these events are expected to be more common in the future. We investigated how three weeks of submergence in water of different salinities affected the photosynthetic rates in seedlings of three common mangroves: Bruguiera gymnorrhiza (L.) Lamk.; Avicennia marina (Forssk.) Vierh.; and Heritiera littoralis Dryand. We found that photosynthesis and survival rates declined with increasing salinity and submergence time for all species. Prolonged submergence caused a significant decline in photosynthetic rates (as electron transport rate – ETR) for B. gymnorrhiza (P = 0.021) and H. littoralis (P = 0.002), whereas significant effects of both salinity (P = 0.003) and submergence (P = 0.023) were observed between species. Maximum diurnal values of ETR declined in the order of A. marina > B. gymnorrhiza > H. littoralis. After submergence, survived seedlings were tended normally, watered twice a day with freshwater. Three seedlings of B. gymnorrhiza from freshwater and 33% seawater treatments and of A. marina from freshwater treatment displayed signs of recovery for the first 3–5 days, but after that they died. We conclude that submergence time and water salinity will affect the performance of mangrove areas, such that areas experiencing prolonged submergence with flooding dominated by saline water might be most severely impacted.

Effects of fragmentation and seawater submergence on photochemical efficiency and growth in the clonal invader Carpobrotus edulis

“…Abou Jaoude et al (2013) have found that saltwater flooding damages plants more severely than freshwater flooding, and Naumann et al (2008) reported that net photosynthesis decreased significantly more after three-days submergence in saltwater compare to freshwater submergence. Interestingly, our results showed a negative effect of seawater in plants that were shallowly submerged for a relatively short period of time, and thus expand previous effects found after a long period of submergence in profundity (Mangora et al, 2014). However, because our design does not include a freshwater submergence treatment, we cannot identify the source (submergence or salinity) of the negative effect encountered in plants under seawater submergence conditions.…”

The Impact of Climate Change on Mangrove Forests

“…A number of studies show species-specific tolerances to prolonged water logging [37][38][39][40]. Common mangroves, such as Avicennia marina, exhibit a high degree of tolerance to water logging, but responses are highly variable in relation to length and water depth of immersion, salinity, temperature, and other environmental factors [41,42].…”

Impact of Global Change on Nutrient Dynamics in Mangrove Forests

“…Mangroves vary greatly in how they respond to a sea level rise and the effect of tidal flooding and such responses appear to be species-specific [52]. For example, Avicennia marina is highly tolerant to prolonged water logging, but responses are highly variable in relation to the water depth of immersion and the length of time as well as salinity, temperature, and other environmental factors [54,55]. There may be other biological responses of mangroves to waterlogging.…”