Proceedings of the Third International Conference on Invasive ...

<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 1: Spartina BiologyFig. 4. Alcohol dehydrogenase (ADH) activities (μmol g -1 min -1 ) <strong>of</strong>Spartina and Distichlis grown under drained and flooded soil treatments.Shown is <strong>the</strong> mean <strong>of</strong> 7-13 plants ± SE. Species are labeled as in Fig. 2.activities in S. anglica were significantly lower than all o<strong>the</strong>rspecies (ANOVA, p≤0.046). Flooded soil conditionsresulted in significantly higher ADH activities in all species(ANOVA, p≤0.018) expect <strong>the</strong> low marsh species S. anglica(ANOVA, p=0.564).Most plants can survive short term absence <strong>of</strong> oxygen(≤60 min) without cell death. In <strong>the</strong>se cases, normal ATPstores are quickly depleted in active cells, and mitochondrialswelling is usually observed within minutes (Drew 1997).Large reserves <strong>of</strong> stored carbon can help <strong>the</strong> cells respireanaerobically, but longer absences <strong>of</strong> oxygen can result incell death. Irreversible damage to mitochondria and cellviability generally occurs following 15 hours <strong>of</strong> anaerobiosis(Perata and Alpi 1993). However, a supply <strong>of</strong> oxygen frominternal aeration can allow marsh plants like Spartina torespire aerobically despite growing in waterloggedsubstrates. The superior oxygen transport abilities <strong>of</strong> S.anglica may have helped to account for its low root ADHactivities observed in this study.The plants studied showed varying degrees <strong>of</strong> sulfideoxidation capacity. Total sulfide oxidation was partitionedinto enzymatic and nonenzymatic processes. The meanenzymatic sulfide oxidase (SOx) activity ranged from 14.4to 97.2 nmol g -1 min -1 across species and waterloggingtreatments (Fig. 5a). Enzymatic SOx activities were highestin <strong>the</strong> high marsh species S. patens and D. spicata and weresignificantly lower in S. densiflora and <strong>the</strong> low marshspecies S. alterniflora and S. anglica (ANOVA, p≤0.050).This difference may suggest that high marsh species aremore sensitive to sediment sulfides and thus require greaterenzymatic protection. Enzymatic SOx activities did notchange in response to flooding across species (ANOVA,p≥0.960).Nonbiotic factors such as metal ions can contribute tosulfide oxidation (Lee et al. 1999). Such nonenzymaticprocesses were also found to be important in sulfideoxidation in <strong>the</strong> present study. Mean nonenzymatic sulfideFig. 5. Sulfide oxidase (SOx) activities (nmol g -1 min -1 ) <strong>of</strong> Spartina andDistichlis grown under drained and flooded soil treatments. Shown are (a.)enzymatic and (b.) nonenzymatic rates <strong>of</strong> sulfide oxidation. The mean <strong>of</strong>4-10 plants are shown ± SE. Species are labeled as in Fig. 2.oxidation rates ranged from 12.6 to 51.1 nmol g -1 min -1across species and waterlogging treatments (Fig. 5b).Nonenzymatic rates <strong>of</strong> sulfide oxidation were not differentbetween species or flooding treatment (ANOVA, p≥0.141).CONCLUSIONSThe upper regions <strong>of</strong> salt marshes are characterized byoxidized soils, since tidal flooding is rare. However, episodicflooding at <strong>the</strong> highest tides can result in occasional anoxicand sulfidic conditions. Therefore, plants from <strong>the</strong> highmarsh are not forced to withstand chronic anoxia. The highmarsh species S. patens, S. densiflora, and Distichlis spicatawere found to have high aerobic respiration rates and highaerobic enzyme activity. This aerobic oxygen demand maybe too high to allow survival in anoxic low marshconditions, where plants had lower aerobic demand.Anaerobic pathways (root ADH activities) increased afterflooding in all three high marsh species suggesting a highsensitivity to soil waterlogging. Internal oxygen transportrates were low in <strong>the</strong>se plants since <strong>the</strong>y are adapted to lifein sediments where soil oxygen is not normally limiting toroot respiration.Additionally, higher SOx activities were found in highmarsh species compared to low marsh species. These trendssuggested that high marsh species were more sensitive tosulfide and required greater protection <strong>of</strong> aerobic respiration.This idea is consistent with <strong>the</strong> finding that <strong>the</strong>se speciesexhibited higher activities <strong>of</strong> CytOx, <strong>the</strong> site <strong>of</strong> sulfideinhibition <strong>of</strong> aerobic respiration (Bagarinao 1992). Highrates <strong>of</strong> aerobic respiration and apparent sulfide sensitivitymay substantially account for <strong>the</strong> exclusion <strong>of</strong> <strong>the</strong>se speciesfrom low marsh zones.The low zones <strong>of</strong> salt marshes are characterized byfrequent tidal flooding. This leads to highly reducedsediments, <strong>of</strong>ten containing high levels <strong>of</strong> sulfides. Plantsinhabiting low marsh regions must be able to tolerate highlyreducing and sulfidic sediment conditions. Spartinaalterniflora is <strong>the</strong> dominant low marsh species in manyNorth American East- and Gulf Coast estuaries (Bertness-51-