THE EFFECT OF INCREASING SALINITY ON THE GROWTH AND ION CONTENT OF 3 NON-HALOPHYTIC WETLAND MACROPHYTES

Increasing salinisation is occurring over large parts of south-eastern Australia. This has potential to impact severely on the biodiversity of wetlands affected by rising saline groundwater and inundated by sal ine water discharged to rivers. Investigations have been made into the effect of salinities of 2, 2-6 (increased over 64 days) and 6 g NaCl l(-1) on the growth, leaf demography and ion concentrations of three w etland macrophytes, Amphibromus fluitans, Potamogeton tricarinatus and Triglochin procera grown in greenhouse troughs. Potamogeton tricarina tus was the most severely affected showing significantly reduced dry w eight and leaf size at 6 g l(-1) along with a reduction in leaf appear ance rate and an increase in leaf death. Triglochin procera was not as severely effected although leaf size was still reduced in 6 g l(-1) t reated plants, Amphibromus fluitans was unaffected by salinity. Na+, K + and Cl- ion contents were determined for leaves of different ages. T he three species exhibited very different patterns of ion accumulation . Amphibromus fluitans excluded Na+ and maintained a low concentration of Na+ in younger leaves relative to older leaves. Potamogeton tricar inatus was saturated in uptake of Na+ at all treatment levels. No leaf age effect was observed, with similar Na+ concentrations in all leave s. The absence of a leaf age gradient may be attributable to a capacit y to absorb Na+ from the water column directly into the leaves irrespe ctive of age. Na+/K+ ratios were lowest for A. fluitans with a strong leaf age gradient of increasing Na+/K+ ratio from younger to older lea ves. Potamogeton tricarinatus was intermediate in Na+/K+ ratio but wit h no clear leaf age gradient. Whereas Na+/K+ ratios ranged from 2 to 8 for A. fluitans and 5 to 15 in P. tricarinatus, T. procera ranged fro m 5 in the youngest leaves to 35 in the oldest leaves. Triglochin proc era like its halophytic relative, Triglochin maritima, had very high N a+/K+ ratios. Triglochin procera may be capable of absorbing Na+ into leaf vacuoles which could be balanced by a high concentration of a com patible solute such as proline in the leaf cell cytoplasm. (C) 1997 El sevier Science B.V.