Mechanism of salt tolerance in endangered semi-mangrove plant Barringtonia racemosa: anatomical structure, photosynthetic and fluorescence characteristics

Abstract

Abstract Barringtonia racemosa is a rare and endangered semi-mangrove plant with salt tolerance (≤ 25‰ salt). However, mechanisms governing the salt tolerance has not been elucidated. Therefore, biomass, photosynthetic and fluorescent characteristics, and anatomical structure of B. racemosa were studied to investigate the mechanism of salt tolerance. The results showed that stem dry weight decreased under high salt stress (30‰-40‰). Net photosynthetic rate, intercellular CO2 concentration of B. racemosa significantly decreased under 35‰ and 40‰ salt treatments, Fv/Fm decreased significantly under 40‰ salt stress, ΦPSI decreased significantly under 35‰ and 40‰ salt stress. The thickness of epidermis of root significantly increased under 25‰ and 40‰ salt treatments. The outer cortex and stele diameters of root significantly increased, under high salt treatments. The xylem and phloem of stem significantly increased under salt treatments, while the cambium and cortex of stem significantly decreased under salt treatments. The width of the increment or stable palisade tissue and spongy mesophyll. Therefore, stable net photosynthetic rate and intercellular CO2 concentration, increment of Fv/Fm and ΦPSI, the increment or stable palisade tissue and spongy mesophyll of leaf and the increment of epidermis, outer cortex, and stele diameter of root could contribute to salt tolerance of B. racemosa.