Anatomia comparada de Clethra scabra Pers. (Clethraceae) em diferentes altitudes na Serra da Mantiqueira em Itamonte, MG, Brasil

Abstract

To verify the influence of altitude on the anatomical structure of leaves and branches of individuals of the species Clethra scabra Pers. (Clethraceae) occurring in the Serra da Mantiqueira, in Itamonte, MG, were collected at altitudes of 1500, 1700, 1900 and 2100 meters. Collected C. scabra leaves and branches were fixed and prepared following the usual procedures of vegetal microtechnique. Quantitative anatomical analyzes were performed using the image analysis software. The leaves of C. scabra are hyposomatic, multiseriate epidermis, presence of stellate hairs ortrichomes in depressions on the abaxial face, dorsiventral mesophyll, palisade parenchyma occupying about 90% of mesophyll and the spongy parenchyma the lowest percentage. The midrib with well-developed xylem and the vascular bundle surrounded by a sclerenchymatic sheath. Data submitted to analysis of variance (ANOVA) and the Scott-Knott test showed that in C. scabra species the thickness of the leaf blade increased significantly with the altitude from 100.72 μm (1500 m) to 142.36 μm (2100 m) and the mesophyll followed the same pattern with increase from 64.16 μm (1500 m) to 92.83 μm (2100 m), as well as from the palisade parenchyma with increases from 41.84 μm to 58.99 μm, and parenchyma spongy from 22.32 μm to 33.84 μm. For the secondary C. scabra xylem, the length of the vessel elements decreased with the altitudinal increase from 565.91 μm (1500 m) to 471.12 μm (2100 m). 38.1μm (1500 m) to 40.77 μm (1700 m), however, at the highest elevations, there was a reduction from 35.01 μm (1900 m) to 30.81 μm (2100 m). Carlquist and mesomorphic vulnerability indices decreased along the elevation gradient from 0.14 (1500 m) to 0.10 (2100 m) and 79.45 (1500 m) to 48.74 μm (2100 m). Fiber length decreases with increasing altitude from 1,224.23 μm (1500 m) to 962.53 μm (2100 m) and the wall thickness of the fiber increased significantly from 4.14 μm (1500 m) to 5.03 μm (2100 m). Altitude had a positive influence of the leaf tissues thickness increase of C. scabra leaf tissue, being thicker and can be interpreted as response to water deficit in the soil and increased water absorption in the form of fog. A significant decrease was observed in vessel element length, tangential diameter, vulnerability and mesomorphy indices as a result of the increase in altitude. At higher altitudes these results may mean greater efficiency and safety in water conduction. The species C. scabra has anatomical leaf and secondary xylem plasticity that are probably responsible for the adaptation of this species to the different environmental conditions imposed by altitude. Thus, it can be inferred that C. scabra leaves and branches have leaf and branch anatomical modifications in the face of environmental conditions along the altitudinal gradient in the RPPN National Heritage Private Reserve in Itamonte, MG.