Salinity tolerance in some mangrove species from Pakistan

Published source details Khan M.A. & Aziz I. (2001) Salinity tolerance in some mangrove species from Pakistan. Wetlands Ecology and Management, 9, 219-223.
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Summary

In coastal regions of southeast Pakistan around the Indus Delta, increases in salinity due to diversion of Indus river water (mainly for irrigation of agricultural land) has led to poor mangrove growth. This situation has been exacerbated by localized extinction of some mangrove species due to pollution, overgrazing and overharvesting. Little information exists on the salt tolerance of Indus Delta mangrove species but this would be of value to enhance success of mangrove restoration efforts. The present study investigated the relative salt tolerance of three local mangrove species Avicennia marina, Ceriops tagal and Rhizophora mucronata.

To assess their potential for degraded coastal mangrove restoration, growth, ionic and water relations of A.marina, C.tagal and R.mucronata were studied in different seawater concentrations. In the summer propagules of A. marina and C. tagal were collected from Indus delta (Sind Province), and R. mucronata from Miani Hor estuary on the Baluchistan coast.

Propagules were planted in 36 cm diameter plastic pots filled with washed beach sand and grown in a greenhouse under natural temperature and light conditions. They were irrigated with fresh water for two weeks, after which they were treated with various concentrations of seawater (0, 25, 50, 75, and 100% - 5 replicate pots containing 5 propagules each). Seawater concentrations were gradually increased by 25% seawater at 2-day intervals to reach the maximum salinity level of 100% seawater after 10 days. Plants were grown for six months and then growth parameters, dry weight and plant height were recorded. Water potential and stomatal conductance were measured, and sodium and chloride content of leaves analysed.

Biomass: After 6 months growth, dry weights of all three mangrove species were maximum in 50% seawater; at increasing salinities (75-100% concentration) growth of R.mucronata and C. tagal were significantly reduceded. At all seawater concentrations, R.mucronata accumulated more biomass, followed by A.marina then C. tagal.

Height: For all three species, height was tallest (A. marina followed by R. mucronata and C. tagal) at 50% seawater and declined with increasing salinity.

Water potential: Water potential became rapidly more negative in A.marina and progressively more negative in C.tagal and R.mucronata with the increase in salinity.

Stomatal conductance: Highest conductance was noted in R.mucronata, followed by A.marina and then C.tagal.

Salt content: Sodium and chloride ions increased with increasing salinity; accumulation was much the highest in A.marina followed by R. mucronata.

Conclusions: These results show that all three species are highly salt tolerant and could probably survive full strength seawater. However, it appears that growth would be enhanced in coastal areas if more freshwater from the Indus River were allowed to flow through the delta to reduce the salinity of coastal seawater. Although all the species studied appear good candidates for mangrove rehabilitation in the Indus Delta, A.marina is best adapted to the conditions of the Pakistani coast as it maintains a very negative water potential under saline conditions.

Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www.springerlink.com/content/j1354321n767p780/fulltext.pdf