SEEDLING RESPONSE TO SALINITY IN FOUR DUNE GRASSES FROM THE OUTER BANKS OF NORTH CAROLINA

Tolerance to salt in the substratum was determined in seedlings of four perennial dune grasses: Ammophila breviligulata Fern., Panicum amarulum Hitch. & Chase., Spartina patens (Ait.) Muhl., and Uniola paniculata L. An inverse linear relationship existed between growth and increased salinity in A. breviligulata, S. patens, and U. paniculata. Panicum ama- rulum seedlings demonstrated a curvilinear response to; salinity. Seedlings of A. breviligulata and U. paniculata grew moderately well in salinities up to 1.0% NaCl, those of P. amarulum achieved even better growth in this salinity range, and some seedlings of S. patens survived the entire 28-day experimental period at 4.0% NaCl. Seedlings of S. patens collected from the field were more salt tolerant than those grown from seed collected from the field and germinated in the laboratory. In the other species the performance of field- and laboratory- grown seedlings did not differ. Based on seedling growth response, the order of decreasing salt tolerance for the four species is S. patens, P. amarulum, U. paniculata, and A. breviligu- lata. This pattern correlates well with performance in nature. ance to burial, sand-blasting, salt spray, drought, and flooding. Although mature plants of these grasses grow together in the dune system, seedlings of sev- eral different species occupy fairly distinct areas or microhabitats. Seedlings of all species are exposed to approximately equal intensities of most environ- mental factors with the exception of flooding with sea water, which is related to elevation. Substrate salinity can damage and kill plants when flooding by salt tides is not accompanied by rainfall in hot, dry weather. Thus, substrate salinity can act as a major selective force determining seedling establishment and survival in areas subject to flooding. The present study was designed to determine substrate salt toler- ance among seedlings of four perennial grasses, Am- mophila breviligulata Fern., Panicum amarulum Hitch. & Chase., Spartina patens (Ait.) Muhl., and Unio~a paniculata L., to see whether this response could be correlated with habitat conditions of seed- ling populations in nature.