Effect of bracteoles on seed germination and dispersal of two species of Atriplex

The influence of bracteoles on the germination response of a salt marsh annual, Atriplex prostrata, and a salt desert perennial, A. griffithii, was determined. Attached bracteoles did not inhibit germination of A. prostrata but completely inhibited germination of A. griffithii seeds. Germination of seeds of A. griffithii was also somewhat inhibited in the presence of detached bracteoles. The osmotic potential of dissolved substances in water-saturated bracteoles was -4.8 +/- 0.05 MPa for A. griffithii and -2.4 +/- 0.15 MPa for A. prostrata. Ash content of bracteoles on a dry weight basis was 28.7 +/- 0.37 % for A. prostrata and 30.0 +/- 0.29 % for A. griffithii. The presence of relatively high concentrations of dissolved salts in bracteoles may explain the reduced germination of A. griffithii. Germination of seeds of the perennial A. griffithii may also be inhibited mechanically by the presence of persistent bracteoles, whereas the annual A. prostrata has ephemeral bracteoles that may serve to limit germination in the autumn but are not present during the normal spring germination period. Bracteoles could affect the dispersal of seeds by water since some fruiting structures of A. griffithii and A. prostrata are able to float in 1.0 % NaCl solutions for 5 and >30 d, respectively, compared with a maximum of 4 and 3 d for seeds without bracteoles. Fruiting structures of A. prostrata floated for longer over a range of salinities than did those of A. griffithii; this may play a significant role in the dispersal of this salt marsh species. (C) 2001 Annals of Botany Company.