ANAEROBIC SUBSTRATE TOLERANCE IN SPOROBOLUS VIRGINICUS (L.) KUNTH.

The purpose of this study was to determine if and how the two genetically distinct forms, marsh and dune, of Sporobolus virginicus (L.) Kunth. tolerate anaerobic substrates. The treatments in the hydroponic study, conducted in the greenhouse for approximately 6 months, involved growing the marsh and dune forms in aerobic, anaerobic, and alternating aeration treatments. Plants were examined for morphological and physiological responses to the aeration treatments. In response to the continuous anaerobic treatment, the dune form of S. virginicus exhibited increased stolon biomass, but no difference of total biomass or rhizome aerenchyma when compared with the aerobic treatment. In response to alternating aeration, rhizome aerenchyma increased, total biomass decreased, and stolon biomass remained constant. Belowground transport of oxygen enabled the root tissue in all of the aeration treatments to maintain aerobic respiration. The marsh form grown in the alternating aeration treatment had the same total biomass but more rhizome aerenchyma when compared to the aerobic treatment. Growth in the continuous anaerobic treatment resulted in a reduction of total biomass and increased rhizome arenchyma. Marsh form roots did not appear to be respiring anaerobically or producing ethanol or additional malate at the time of harvest; however, root respiration was higher in the anaerobic and alternating treatments. The marsh and dune forms of S. virginicus were able to adjust morphologically or physiologically or to use existing morphological features to tolerate anaerobic substrates. Thus, it appears that the distribution of the two forms of S. virginicus found in coastal sand dunes and in salt marshes is not limited by differences in ability to tolerate waterlogged soils. SINCE Sporobolus virginicus (L.) Kunth., a grass of worldwide distribution in the tropics and sub-tropics, is found in both wetland and nonwetland habitats, its anaerobic substrate tolerance capacity is of interest. A perennial with numerous branching and creeping rhizomes, it typically forms extensive colonies on sandy or muddy seashores and in saline marshes (Hitchcock, 197 1). Sporobolus virginicus has two genetically distinct growth forms which because of their distributions are designated here as marsh and dune forms. The marsh form is listed as the type specimen of S. virginicus by Hitchcock (1971) and is described as var. mil Received for publication 14 January 1984; revision accepted 16 August 1984. This research was supported by U.S. Environmental Protection Agency, Corvallis Environmental Research Laboratory through grant number R-806824010, and the office of Sea Grant, NOAA, through the University of Delaware Sea Grant College Program Project R/B12, grant number NA80AA-D-00106. Manuscript preparation was suported by Contract DE-AC09-76SR00819 between the U.S. Department of Energy and the University of Georgia's Savannah River Ecology Laboratory. 2 Present address: Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29801. nor Bail. by Smith-White (1979) in Australia. It has blades approximately 5 cm in length, culms 10-40 cm in height, and grows at the fringes of saltpans, in the low and high marsh, and along river banks. The dune form is listed as a robust form of S. virginicus by Hitchcock (1971) and is referred to as var. virginicus by Smith-White (1979). It has culms up to 1 m in height, longer and broader leaves, and generally occurs on sandy beaches and coastal dunes. Sapelo Island, Georgia (approx. 31°25'N latitude and 8 1°1 5 'W longitude) is the northern most reported collection site where both forms grow in adjacent habitats in North America (Gallagher, 1979). When raised from seed under identical conditions the two forms retain their divergent morphological characteristics. The occurrence of both the marsh and dune forms on Sapelo Island provided an opportunity to look for intraspecific diffierences in the anaerobic substrate tolerance characteristics of S. virginicus. Breen, Everson and Rodgers (1977) studied the effiects of salinity and inundation on various ages of young marsh form S. virginicus plants growing in pots. They found that the young plants are sensitive to inun-