Abstract
Rhizophora mangle L. is one of the most distributed species of neotropical mangroves. The species exhibits great phenological variability that is associated with saline concentrations of the sediment where it grows. Among the organs that are most affected by interstitial and tidal water salinity concentrations are the leaves. Since the hypersalinity generates water deficiency, it changes photosynthetic and hydraulic processes of the plant. To understand the relationship between the variation in leaf blade parameters and the water stress generated by salinity in two growth stages, morphoanatomical functional traits were quantified in leaves of juveniles and adults of R. mangle in three structurally different mangrove forests with different ranges of natural salinity (Oligohaline: 5.8–11.7 practical salinity units (PSU); Euhaline: 9.2–35.6 PSU and 23.9–47.7 PSU). We hypothesized that water stress caused by salinity generates modification in conductivity, water-storage, and photosynthetic tissues. Our results showed a greater number of morphoanatomical traits affected by salinity in juveniles compared to adults, greater variability in the traits associated with water accumulation and transport. Adults and juveniles subjected to higher values of salinity had traits more tolerant of variability in this factor, allowing superior adaptation to environments with high water deficit than individuals originating in oligohaline environments. This difference in adaptability to salinity between populations of R. mangle may imply different responses to climate change, where populations of oligohaline origin will be more susceptible to hypersalinization resulting from this phenomenon, while populations of euhaline origin could more effectively tolerate the aquatic stresses caused, allowing a prolongation of their permanence and the provision of their ecosystem services over time.
Highlights
IntroductionIt is widely distributed from the Caribbean of the Florida Peninsula to Brazil and on the Pacific Coast from Mexico to Chile [2,4]
The three forests evaluated determine the presence of a salinity gradient on the San Andrés island in a southeastern–northeastern direction that explains the structural differences between the populations of R. mangle of each forest and the variation in the functional traits of the leaf
The functional traits evaluated determine that there is a greater difference between the juvenile groups because they are in a state of adaptation to the fluctuation of water stress due to salinity, generating a greater plasticity in the traits in order to stabilize to the environmental conditions of the environment
Summary
It is widely distributed from the Caribbean of the Florida Peninsula to Brazil and on the Pacific Coast from Mexico to Chile [2,4] It is a successional pioneer species [5] that has an optimal growth range at salinities between 8 and 60 practical units of salinity–PSU (practical salinity units) [6] and develops an ultrafiltration mechanism at the level of root cells to prevent the entry of excess solutes [7]. It can develop tree or shrub morphology [8] reaching up to 30 m tall and 100 cm DBH [9,10]. A water efficiency mechanism face to water deficit which limits the transport of photosynthetic electrons, affecting carbon reduction processes [16] and increase in relative water content in the leaves of individuals subjected to low salinities [13]
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