MORPHOLOGICAL AND PHYSIOLOGICAL-RESPONSES OF SCAEVOLA-SERICEA (GOODENIACEAE) SEEDLINGS TO SALT SPRAY AND SUBSTRATE SALINITY

The effects of substrate salinity and salt spray upon seedlings of Sca evola sericea were examined in this study. Three levels of substrate s alinity: 0.0 ppt, 3.0 ppt, and 10.0 ppt were examined in conjunction w ith three levels of salt spray: zero, medium (approximate to 200 mg . m(-2). d(-1)), and high (approximate to 1200-1500 mg . m(-2). d(-1)). Leaf surface area, root to shoot ratio, as well as leaf, stem, and roo t mass decreased significantly (P less than or equal to 0.05) with inc reasing substrate salinity. Biomass accumulation was very low at 10.0 ppt substrate salinity, suggesting that higher levels of substrate sal inity cannot be tolerated by the seedlings. Salt spray had a substanti al effect on several of these variables, however its effects were less pronounced than those of substrate salinity. Cell sap osmolarity, lea f thickness, and leaf specific mass increased significantly (P less th an or equal to 0.05) with both increasing substrate salinity and salt spray levels. Leaf carbon isotope ratios (delta(13)C) became more posi tive with increasing salinity, indicating an enhancement of the intrin sic water use efficiency of the seedlings at higher salinities. Scaevo la sericea is one of the dominant plants found at the leading edge of strand communities in the Hawaiian archipelago and throughout much of the tropical Pacific. Since substrate salinity and salt spray increase with proximity to the ocean, the two factors may act together to limi t the seaward expansion of S. sericea in coastal habitats.