Ecological Anatomical Characteristics of Secondary Xylem in Kandelia obovata Sheue et al.

Five soil physicochemical indexes, including edaphic pH, edaphic salinity and soil nutrient values, were determined in seven Kandelia obovata populations located in the Futian Mangrove Nature Reserve of Shenzhen Bay. The morphological features of the secondary xylem of K. obovata populations corresponding to soil sampling, which represented different habitats, were surveyed by light microscopy (LM), scanning electron microscopy (SEM), laser scanning confocal microscopy (LSCM) and transmission electron microscopy (TEM). Variations in the quantitative wood anatomical features of the seven K. obovata populations were assessed in detail. Relationships between soil physicochemical variables and quantitative wood anatomical features were analyzed statistically. Some specialized wood structures in K. obovata growing in different habitats were observed, suggesting that they function to safely conduct water under high negative pressure and are adaptive to intertidal habitats. Their characteristics included some fibriform vessel elements and a few vasicentric tracheids; abundant micromorphological structures such as vestures and helical structures on vessel walls, and vestured pits and perforated plates. The relationship between soil physicochemical factors and quantitative anatomical features by stepwise regression analysis indicated that larger-scale vessel elements occurred with increasing soil Na ⁺ content and total salt quantity. Large scale vessel elements improved the water transportation efficiency, but depressed water transportation safety. Presumably, other wood anatomical features might ensure safe mechanisms for K. obovata under conditions of higher soil ion content and larger scale vessel elements, which both result in lower water transportation safety.