Seedling responses to salinity of 26 Neotropical tree species

Abstract

Sea-level rise will result in increased salinization of coastal areas. Soil salinity is a major abiotic stress that reduces plant growth, yet tolerance to salinity varies across environmental conditions, habitats and species. To determine salinity tolerance of 26 common tropical tree species from Panama, we measured growth, gas exchange and mortality of 3-month-old seedlings subjected to weekly irrigation treatments using five seawater solutions (0 % = control, 20, 40, 60 and 90 % V/V of seawater) for ~2 months. In general, species from coastal areas were more tolerant to increased seawater concentration than inland species. Coastal species such as Pithecellobium unguis-cati, Mora oleifera, Terminalia cattapa and Thespesia populnea maintained growth rates close to those of controls at 90 % seawater. In contrast, inland species such as Minquartia guainensis, Apeiba membranacea, Ormosia coccinea and Ochroma pyramidale showed strong reductions in growth rates and high mortality. Plant height and leaf production also differed greatly between the two groups of plants. Furthermore, measurements of gas exchange parameters, i.e. stomatal conductance and maximum photosynthetic rate, were consistent with the contrasting growth responses of coastal and inland species. Our research reveals a great degree of variation in salinity tolerance among tropical tree species and demonstrates a close relationship between species habitat and the ability to thrive under increasing salt concentration in the soil, with coastal species being better adapted to withstand increased soil salinity than non-costal species.

Keywords: Mortality; photosynthesis; relative growth rate; salt tolerance; stomatal conductance; tropical trees.

Figure 1.

Stem height reduction at 90 % of seawater irrigation treatment (±SE) in coastal and inland species. See Supporting Information for all other seawater treatments figures.

Figure 2.

Leaf production at 90 % of seawater irrigation treatment (±SE) in coastal and inland species.

Figure 3.

Relative growth rates as percentage of control (±SE) for all studied species across seawater treatments. Panels are arranged in relation to Table 1.

Figure 4.

Plant mortality by species given as percentage under 90 % seawater irrigation treatment (±SE) for coastal and inland species. Panel letters indicate groupings according to their tolerance.

Figure 5.

Stomatal conductance (g_s) across time (±SE) under control conditions, and at 60 and 90 % of seawater for coastal and inland species. Data represent averages of 3–5 individuals.

Figure 6.

Maximum photosynthetic rate (A_max) across time (±SE) under control conditions, and at 60 and 90 % of seawater for coastal and inland species. Data represent averages of 3–5 individuals.

Figure 7.

Cladogram representing species salinity tolerance ranking according to a hierarchical clustering analysis using all response parameters, except g_s and A_max, under 90 % seawater treatment. Within each clade, species are arranged by ascending ranking of salinity tolerance.