ELSEVIER Aquatic Botany 58 (1997) 73-88 The effect of increasing salinity on the growth and ion content of three non-halophytic wetland macrophytes Nigel W.M. Warwick *, Paul C.E. Bailey Dept. of Ecology and Evolutionary Biology and Cooperative Research Centrefor Freshwater Ecology, Monash Universi~', Clayton, Vic. 3168, Australia Accepted 24 September 1996 Abstract 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 saline water discharged to rivers. Investigations have been made into the effect of salinities of 2, 2-6 (increased over 64 days) and 6 g NaCI 1- ~ on the growth, leaf demography and ion concentrations of three wetland macrophytes, Amphibromus fluitans, Potamogeton tricarinatus and Triglochin procera grown in greenhouse troughs. Potamogeton tricarinatus was the most severely affected showing significantly reduced dry weight and leaf size at 6 g 1- ~ along with a reduction in leaf appearance rate and an increase in leaf death. Triglochin procera was not as severely effected although leaf size was still reduced in 6 g 1- i treated plants. Amphibromus fluitans was unaffected by salinity. Na +, K + and CI- ion contents were determined for leaves of different ages. The three species exhibited very different patterns of ion accumulation. Amphibro- musfiuitans excluded Na + and maintained a low concentration of Na + in younger leaves relative to older leaves. Potamogeton tricarinatus was saturated in uptake of Na + at all treatment levels. No leaf age effect was observed, with similar Na ÷ concentrations in all leaves. The absence of a leaf age gradient may be attributable to a capacity to absorb Na + from the water column directly into the leaves irrespective 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 leaves. Potamogeton tricarinatus was intermediate in Na+/K + ratio but with 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 from 5 in the youngest leaves to 35 in the oldest leaves. Triglochin procera like its halophytic relative, Triglochin maritima, had very high Na+/K + ratios. Triglochin procera may be capable of * Corresponding author. 0304-3770/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0304-3770(96)01104-7