Exploring the fast-growing mechanism of Laguncularia racemosa from the perspective of leaf traits and ultrastructure

Abstract

Leaf traits and chloroplast structure have a direct impact on plant growth rates. Fast-growing species allocate more carbon to growth, and slow-growing species invest more in storage. This study was conducted to investigate the fast-growing mechanism of the introduced mangrove species Laguncularia racemosa, by comparing the leaves of L. racemosa and three slow-growing native mangrove species (Kandelia obovata, Avicennia marina, and Aegiceras corniculatum) through analysis of anisotropic growth of leaf traits and leaf chloroplast ultrastructure. The results showed that the largest slope values were found in the leaf area compared to leaf perimeter relationship (2.035), while the slope of the leaf perimeter compared to leaf width relationship was only 0.832. And the leaf area of A. marina was most influenced by leaf perimeter, while the leaf area of L. racemosa was least influenced by leaf perimeter. Furthermore, the average area of thylakoid lamellae per chloroplast was the largest in L. racemosa leaves, with no accumulation of starch granules detected. While most of the chloroplast area of three native mangrove species was occupied by starch granules and lipid droplets, resulting in a reduction in the thylakoid lamellae contained per unit area of the chloroplasts. These results imply that the chloroplasts of L. racemosa can transport photosynthetic products to other organs of the plant in a timely manner, maximizing the area of thylakoid lamellae in the chloroplast and enabling its leaves to maintain high photosynthesis for its rapid growth.