Leaf anatomical adaptation of eighteen mangrove plant species from the Sundarbans in Bangladesh

Abstract

Investigation on leaf anatomical adaptation of 18 mangrove plant species was carried out. Among the 18 species 13 were dorsiventral and five were isobilateral type. All the species had special stomatal structure and variable cuticle layer to minimize transpiration. Most of the species had succulent leaves with leaf thickness ranging from around 232 to 1363 μm. As an indication of salt secretion, both glandular and non-glandular trichomes were observed in several species. Although presence of single to multilayered hypodermis might effectively function as water storage tissue, several studied mangrove plant species e.g. Cynometra ramiflora L., Phoenix paludosa Roxb., Pongamea pinnata (L.) Pierre, Sonneratia apetala Buch. - Ham., S. caseolaris (L.) Engl. and Xylocarpus moluccensis (Lamk.) M. Roem. showed complete absence of hypodermis. This might be due to moderate saline condition. In addition, marked terminal tracheids in mesophyll tissue of a number of species might help with capillary water storage within the leaf. To enhance mechanical support several species were found to develop considerable amount of diverse sclereids within the mesophyll tissue and surrounding vascular bundle. Although maximum anatomical adaptations are common for plants growing in saline habitat it may be suggested that these features were differentially developed in plants specifically grown in mesohaline zone.

Novel leaf-root coordination driven by leaf water storage tissues in mangroves

“…( b ) In non-mangrove plants, we observe a similar pattern of traits decoupling between leaf economics and leaf hydraulics, suggested by the largely orthogonal alignment between the two groups of traits (blue vs. green). Traits abbreviation: LTh, leaf thickness ; LMA, leaf dry mass per area ; N mass , leaf mass-based nitrogen concentration ; δ 13 C, leaf carbon isotope composition ; SLA, specific leaf area ; LTD, leaf tissue density ; Tphol, total phenol content ; WST, water storage tissues ; LV dia , leaf minor vein diameter ; LV den , leaf minor vein density ; SL, stomatal guard cell length ; SD, stomatal density ; g wmax, maximum stomatal conductance to water vapor .…”

“…( b ) In contrast with mangrove trees, root traits of non-mangrove plants appear to be orthogonal to leaf economics traits. Abbreviations of the traits are: LTh, leaf thickness ; LMA, leaf dry mass per area ; N mass , leaf mass-based nitrogen concentration ; δ 13 C, leaf carbonisotope composition ; SLA, specific leaf area ; LTD, leaf tissue density ; Tphol, total phenol content ; WST, water storage tissues ; LV dia , leaf minor vein diameter ; LV den , leaf minor vein density ; Diam, root diameter ; ToS, thickness of root tissues outside the stele ; Stele, root stele diameter ; Stele : Diam, stele to root diameter ratio ; SL, stomatal guard cell length ; SD, stomatal density ; g wmax, maximum stomatal conductance to water vapor .…”

“…The copyright holder for this preprint (which this version posted July 28, 2022. ; https://doi.org/10.1101/2022.07.26.501578 doi: bioRxiv preprint most non-mangrove plants, mangrove plants usually have remarkable water storage tissues in their leaves to adapt to physiological drought caused by high-salinity environments 34 . For example, it has been reported that the mangrove plant Avicennia marina can maintain a normal transpiration rate for up to 2 h under water supply from leaf water storage tissues without water supply from roots 35,36 .…”

“…This is partially consistent with our second hypothesis for mangrove plants. Generally, under drought or physiological drought caused by high salinity, plant roots and vessels tend to be thinner 11,21,41,42,43 , whereas leaf water storage tissues usually increases 34,35,39 . These contrasting trends will cause a negative relationship between root diameter (representative of root hydraulics) and leaf water storage tissues (representative of leaf economics) in mangrove plants, which was confirmed by our results (Fig.…”

“…It remains unclear whether the decoupling between leaf hydraulics and economics still holds and whether the above novel mechanism accounting for such decoupling can be applied to plants under stressful environments such as coastal mangrove species that typically grow under high salinity and are confronted with severe physiological drought 5,10,11 . One conspicuous characteristic of mangrove plants is that they usually have significant water storage tissues in their leaves as an adaption to the imperative water demanding of transpiration under drought stress 12,13,14,15,16 . Meanwhile, plants usually adjust above- and belowground organs (e.g., leaves vs. roots) in a coordinated manner during plant evolution and response to changing environments 4,17,18,19,20,21 .…”