Experimental assessment of salinity tolerance of Ceriops tagal seedlings and saplings from the Indus delta, Pakistan

Propagules of Ceriops tagal (C. tagal) collected from the Indus delta were grown in pots containing sandy soil sub-irrigated with 0, 25, 50, 75 and 100% seawater fortified with nitrogen. Seedlings were experimentally grown for 6 months and saplings for 12 months. Maximum growth was observed in 50% seawater and declined with increasing salinity. Water relations data showed that this species progressively adjusted its internal water potential in response to change in external water potential, i.e. responded as an osmoconformer. C. tagal is also a non-secretor and accumulated a larger quantity of sodium and chloride ions while availability of other ions were severely restricted. Our result suggests that C, tagal is almost as salt tolerant as Avicennia marina but would not be able to tolerate a sudden major shift in salinity. This species could, thus, probably be used to rehabilitate inter-tidal areas, which receive a regular supply of fresh water. (C) 2001 Elsevier Science B.V. All rights reserved.