Chemical and mechanical properties of the leaf cuticular membranes (CMs) of a mangrove, Sonneratia alba J. Smith, were analysed at various leaf development stages to evaluate their tolerance to environmental stress. Our analyses demonstrate that the CMs from leaves of S. alba at different growth stages are generally rich in wax (21.5–25.7%) and cutin (52.4–63.4%) which rapidly accumulate at the early stages of leaf growth, while cutan (4.3–10.3%) and polysaccharide (2.3–7.7%) continuously accumulate throughout growth. Immature CMs are physically weak and highly viscoelastic. However, CMs become strengthened and stiffened during leaf expansion and maturation (by factors of about 1.5 and 2.4, respectively) while their flexibility decreases (68–83% decrease). Finally, the CMs lose their strength at the senescent stage (30–43% decreasement). Correlation analysis between chemical composition and mechanical properties revealed that the cutin matrix is mainly responsible for the high viscoelastic properties of CMs, while wax, cutan and polysaccharide contributed to their elasticity. Wax also affected the strength of the CMs, whereas cutan and polysaccharide showed rigidizing effect. Rapid accumulation of wax and cutin in the CMs after bud burst followed by the mechanical supports of cutan and polysaccharide in an isolateral manner contributed to the remarkable environmental tolerance of S. alba.

Carbon export from mangrove forests to the oceans partly acts as a sink for atmospheric CO₂, exceeding the rate of carbon burial in mangrove soils. Primary production in ecosystems adjacent to mangroves may prevent degassing and enhance further carbon export from mangroves to the oceans. In this study, we continuously monitored carbonate chemistry parameters (pCO₂, dissolved inorganic carbon (DIC), total alkalinity (TA)) and dissolved organic carbon (DOC) in a tidal flat adjacent to a fringe mangrove forest over a spring-neap tidal cycle. Mean pCO₂ during the entire period was 923 ± 318 μatm, and the export of TA, DIC, and DOC from the mangroves to the ocean was 36 ± 26 mmol m⁻² d⁻¹, 42 ± 39 mmol m⁻² d⁻¹, and 10 ± 9 mmol m⁻² d⁻¹, respectively. Semi-monthly pCO₂ variations in the mangrove front were controlled by the tidal level during spring tide and by photosynthesis and respiration on the tidal flat during neap tide. This means that during neap tide, photosynthesis on the tidal flat offset the increase in pCO₂ caused by the porewater export from the mangrove soil. The DIC/TA export ratio in this study was 1.17 ± 0.08, which was lower than the global average of 1.41 ± 1.39, indicating that the tidal flat adjacent to the mangrove forest may act as a buffer zone to mitigate the increase in pCO₂, resulting in much of the exported DIC being stored in the ocean.

Background: The mangrove species Bruguiera gymnorrhiza (L.) Lam. and Rhizophora stylosa Griff. are found in riverine mangrove forest, where the trees occur in mixed forest. They have different ecological traits and supporting buttress root systems. However, little is known about the bark and wood structural properties of the trees which are important when using biomechanical approaches to understand the ecological differences between species. Here we test the hypothesis that the structural properties of the trees are influenced by the ecology of these species in riverine mangrove forest. Methods: Plots were established in mixed forest of B. gymnorrhiza and R. stylosa in riverine mangrove forest on Iriomote Island in Okinawa, Japan. Selected trees from the two species were sampled to evaluate the bark and wood properties of the stems, branches and roots. The data were analysed and compared for the two mangrove species. Results: Bruguiera gymnorrhiza and R. stylosa have differences in their bark and wood properties. R. stylosa trees have thicker bark and higher bark density, and wood of higher density, strength, stiffness, and hardness. This applies to the stems and roots of R. stylosa trees, and supports the compressive buttresses, and exposed tidal positions of this light demanding pioneer species. Bruguiera gymnorrhiza trees have a higher proportion of wood in the stems and branches, and less in the roots, which can be attributed to the risk of canopy damage, and the presence of tensile buttresses, in this shade-tolerant gap-phase species. Conclusions: Differences in the bark and wood properties of the stems, branches and roots, were consistent with the ecological traits of B. gymnorrhiza and R. stylosa, and the structural properties of the buttress root systems. The knowledge will aid understanding of the distribution of these species in riverine mangrove forest.