RELATIVE GROWTH OF SPARTINA-PATENS (AIT) MUHL AND SCIRPUS-OLNEYI GRAY OCCURRING IN A MIXED STAND AS AFFECTED BY SALINITY AND FLOODING DEPTH

Mixed stands of Spartina patens and Scirpus olneyi occur in brackish marshes along the Gulf Coast of Louisiana. Scirpus olneyi is considered to be an important wildlife food, and marshes are often managed to favor its dominance over S. patens. Two environmental factors that affect growth of the two species are salinity and water regime. The objectives of this study were to determine the effects of salinity and water depth, under controlled greenhouse conditions, on relative dominance of the two species, chemical properties of soil interstitial water, and nutrient concentrations in the plant tissue. Treatments imposed in a factorial design were salinities of 0, 5, 10, 15 and 20 ppt and water depths of -10, +10, and +30 cm relative to the soil surface. Results indicated that salinity treatments above 10 ppt reduced growth of both species, but S. olneyi was more drastically affected than S, patens. Increased flooding depth reduced growth of S. patens but had little effect on S. olneyi. Concentrations of inorganic ions (Na+, K+, Mg+2, Ca+2, Cl-1) in plant tissue were greater in S. olneyi than S. patens, indicating that ion accumulation may be the principal salt tolerance mechanism of S. olneyi. Extrapolated to held conditions, these results indicate that increasing salinity favors productivity of S. patens relative to S. olneyi, while increased depth of flooding favors S. olneyi.