Seedling Growth and Quality of Avicennia marina (Forssk.) Vierh. under Growth Media Composition and Controlled Salinity in an Ex Situ Nursery

Abstract

Avicennia marina (Forssk.) Vierh. is an important mangrove species that inhabits the outermost zone of mangrove forests, but it has been shown to have a poor ability to regenerate due to its low seedling quality. We conducted a study to evaluate the specific growth requirements of A. marina, i.e., medium and salinity level. Germinated seeds were transplanted to pots filled with media, i.e., silt loam (M1), loam (M2), sandy loam (M3), or sand (M4), with various salinity levels 5 (S1), 5–15 (S2), 15–25 (S3), or 25–35 ppt (S4). Survival rate, growth, biomass partition, and seedling quality were observed for 14 weeks after transplanting the seeds. The highest rate of seedling survival was found in the S2 condition, and higher concentrations of salinity lowered the survival rates. The S1 treatment promoted the initial 8 week growth of the seedlings. Growth medium had no significant effect, except on the survival rates grown in M4. Growth medium composition had no distinct effect on seedling growth. The S2 and S3 treatments induced better growth (in terms of shoot height and root length) and resulted in high-quality (i.e., Dickson quality index) seedlings in any type of medium. The S3 treatment increased the seedling quality in M1 and M4, whereas the S4 treatment only benefited seedlings in the M4 medium. According to the results, a specific range of salinity (5–15 ppt) with circulated water in any type of medium is recommended for the establishment of an ex situ nursery for the propagation of A. marina, in contrast to the general range of salinity (4–35 ppt) stated in previous references.