DIMETHYLSULPHONIOPROPIONATE (DMSP) IN SPARTINA-ALTERNIFLORA LOISEL

Dimethylsulphoniopropionate (DMSP) in saltmarsh grasses of the genus S partina has been suggested to act as a compatible osmolyte or as an in termediary product of a sulphide detoxification mechanism. Investigati ons of Spartina alterniflora Loisel. plants collected from salinity an d sulphide gradients along a South Carolina river showed that DMSP con centrations were not correlated with either salinity or sulphide conce ntrations in soil porewater. This suggested that DMSP is neither a com patible osmolyte nor involved in sulphide detoxification. Greenhouse e xperiments were also performed, investigating the effects of sulphate, sulphide and ammonium nitrate on DMSP concentrations in the plants. O nly ammonium nitrate affected DMSP concentrations, which decreased in the shoots upon increasing nitrogen amendments. It is suggested that n itrogen stimulates biomass production, leading to dilution of DMSP con centrations. Ammonium nitrate amendments also decreased the fraction o f total sulphur in the shoots allocated to DMSP, which ranged between 36 and 86%. The data suggest that nitrogen plays a key role in determi ning DMSP concentrations in plants of the genus Spartina and that DMSP is not involved in a sulphide detoxifying mechanism. Alternative hypo theses for the functions of DMSP in Spartina alterniflora are suggeste d.