Determining the Effects of Salinity and Light on Key Ecophysiological Traits of Two Nonnative Mangrove Species in China

Sonneratia apetala and Laguncularia racemosa are two nonnative mangrove species in China, having been widely planted in mangrove afforestation. This study aimed to assess the ability of the seedlings for these two species to withstand different seawater salinities and shading levels under magnitude, as well as to investigate the combined effects of salinity and light on growth performance. The experiment had five treatments of salinity (0, 10, 20, 30, and 40 practical salinity units [psu]) and five treatments of light intensity (100, 80, 60, 40, and 20% photosynthetically active radiation [PAR]) over the process of the 90-day cultivation. Throughout the experimental period, seedlings of both species manifested the traits of stressed status, including height, growth rate, and photosynthetic rate. The S. apetala seedlings were more sensitive to salinity and low light intensity than L. racemosa. The seedling height of L. racemosa was less affected by middle-level salinity (10 and 20 psu) and light intensity (60 and 80% PAR). Photosynthetic rates and transpiration rates of L. racemosa leaves were recorded as two times higher than those of S. apetala, especially under 0- and 20-psu treatments. L. racemosa seedlings had better adaptation in growth and leaf physiology under severe environmental stress (e.g., 30 psu and/or 20% PAR) than S. apetala. These findings illustrated that L. racemosa at higher salinity and wider shade exhibits superiority over S. apetala, leading to more biological invaded potentiality.