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Rapid growth in height is an important mechanism used by many emergent wetland macrophytes to withstand water depth increases, particularly in species unable to maintain sufficient rates of photosynthesis and gas exchange for long-term survival underwater. However, increases in salinity can reduce growth rates and above-ground biomass production in non-halophytic macrophytes and this may reduce their inundation tolerance. We tested this hypothesis by comparing growth responses of Cynodon dactylon (L.) Pers, Paspalum distichum L., Eleocharis equisetina C.Presl and Bolboschoenus caldwellii (V.J.Cook) Sojak at three depths (5, 20 and 60 cm) across four salinity treatments (200, 2500, 5000 and 10 000 mg L −1 ) . Increases in depth had negative effects on the growth of all four species. The three emergent wetland macrophyte species ( P. distichum , E. equisetina and B. caldwellii ) grew more rapidly, produced more above-ground biomass, and/or maintained positive growth rates at greater depths in the lower salinity treatments than at higher salinities. The terrestrial grass species, C. dactylon , displayed negligible growth when waterlogged and where biomass decreased significantly with depth, there were no significant differences in biomass between the salinity treatments. We conclude that increases in salinity reduced the ability of the three emergent wetland macrophyte species to withstand increases in water depth. The potential depth ranges of these species are therefore likely to change within wetlands if salinisation occurs. Specifically, the habitat ranges of these species are likely to contract and shift towards the shallower, less-frequently flooded limits of their current ranges as salinity levels become limiting to growth.

Wetlands in the Keoladeo National Park, Bharatpur, India, have been dominated by the grass Paspalum distichum L. since the removal of cattle and water buffalo from the park in the early 1980s. The mean water depth was lowest just before the onset of monsoon, highest immediately after it, and then declined slowly over the winter and spring. The mean cover of P. distichum was also lowest just prior to the onset of the monsoon (e.g. 19% in June 1984), increased after the monsoon (e.g. 35% in October 1985) and did not reach its maximum until late winter (e.g. 49% in March 1985). There was relatively little change in the species composition of the vegetation over an annual cycle. Because of the poor monsoon in 1986, water depths were much lower during the post-monsoonal period than normal. The cover of P. distichum was also reduced during this period and fell to only 2% by March 1987. The seed banks of areas dominated by Paspalum and four other emergent species contained a total of 55 species and between 1100 and 3100 seeds m−2. Seeds of P. distichum were found in all vegetation types. Paspalum-dominated areas grazed by geese had a seed bank that contained 44 species and a mean of about 1000 seeds m−2. Only goose droppings collected in November contained viable seeds, of which 90% were Paspalum seeds. Paspalum litter (6 cm or more) reduced recruitment from the seed bank by about 80% and the number of species recruited by about 50%. Only 12 species (total seedling density

In an experimental study conducted in north-central India, four plant species were either clipped weekly, clipped every 2 weeks, or left unclipped while growing at one of three water levels (0, 3 or 13 cm above the soil surface). When clipped underwater, individuals of three emergent species, Ipomoea aquatica Forssk., Paspalidium punctatum A. Camus, and Paspalum distichum L. usually died, but those of Nymphoides cristatum Kuntze did not. Clipped plants of N. cristatum had as much total biomass as unclipped plants, with increased mean shoot biomass but reduced mean root biomass in 3 cm of water. The three emergent species lived when clipped every 2 weeks in 0 cm of water. Clipped plants of emergents had less total mass and less root mass than unclipped plants in 0 cm of water. In a field study in a monsoonal wetland in the Keoladeo National Park, plants of Ipomoea aquatica and Paspalum distichum, died when clipped underwater.