Salinity responses of inland and coastal neotropical trees species

Abstract

Salinization of coastal lands by sea-level rise means that information on the response of tropical tree species to salinity is urgently required to effectively manage coastal systems under future climatic scenarios. While salinity represents a major selective abiotic stress, little is known about the underlying mechanisms determining salinity tolerance in tropical trees. We examined salinity responses in seedlings of eight neotropical tree species from Panama, including four coastal species (Sterculia apetala, Pithecellobium ungi-cati, Terminalia cattapa, and Thespesia populnea) and four inland species (Minquartia guianensis, Apeiba membranaceae, Ochroma pyramidale, and Ormosia macrocalyx). Three-month-old seedlings of each species were subjected to increasing concentrations of 80, 120, 200, and 300 mM of either NaCl or KCl, while controls were irrigated with tap water. Overall, growth parameters such as leaf area (LA), leaf area ratio (LAR), stem height (SH), total dry mass (TDM), and relative growth rates (RGR) were reduced for all species as salinity increased, regardless of salt treatment. However, species from coastal environments outperformed inland species at high salinity. For example, seedlings of coastal species growing in 300 mM of NaCl or KCl, corresponding to ~ 50% seawater, survived and maintained LA, SH, and TDM between 50 and 90% compared with control plants. In contrast, inland species showed reductions in RGR, LA, and SH of up to 100%, at 120 mM of either salt. At the foliar level, K⁺ accumulation remained similar under NaCl and KCl treatments, and almost all species, with the exception of Minquartia from inland forests, maintained foliar Na⁺ accumulation across treatments when compared to controls. While species from coastal environments maintained foliar Cl⁻ under NaCl and KCl treatments, inland species such as Ochroma showed up 95% increase in foliar Cl⁻. Our results suggest that salinity tolerance among tropical trees is predetermined by habitat association and ultimately by the ability of species to manage toxicity associated to foliar Na⁺ and Cl⁻. While the ecological implications of sea-level rise in coastal vegetation require further examination, is foreseeable that adaptation strategies in tropical shorelines consider the use of coastal species (i.e., reforestation) as the best tool to ameliorate the impact of increased salinity.