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<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 1: Spartina Biologyrespective treatment (drained or flooded) before testing orharvest. All statistical analyses were performed betweenspecies and treatments with a two-factor (species andtreatment) analysis <strong>of</strong> variance (Statview 5; 1998 SASInstitute Inc., Cary, NC; α=0.05).Individual plants were tested for <strong>the</strong>ir ability to transportoxygen internally after <strong>the</strong> method <strong>of</strong> Maricle and Lee(2002). A fiber optic oxygen-sensing probe (FOXY-R probe;Ocean Optics Inc., Dunedin, FL) was used to measuredissolved oxygen concentrations in sealed flasks containingroots <strong>of</strong> intact plants suspended in water. Flask watercontained penicillin G and streptomycin sulfate at 1 gramper liter (1 g L -1 ) each and 50 mg L -1 chloramphenicol toprevent bacterial respiration. During testing, plants wereplaced under a 250 watt (W) metal halide light (Hydr<strong>of</strong>armgardening products; Petaluma, CA). At plant level, PPFDwas about 150 μmol quanta m -2 s -1 and air temperature was28˚C. Flask dissolved oxygen concentrations started at 100μM (±10 μM) and were measured over a period <strong>of</strong> 2-3 hoursto observe consumption or release <strong>of</strong> oxygen by plants to <strong>the</strong>surrounding medium.Parallel measurements <strong>of</strong> oxygen consumption wereconducted on plants where aerenchyma transport capabilitieswere blocked. Placing <strong>the</strong> shoot <strong>of</strong> <strong>the</strong> plant in a 100% N 2atmosphere prevents <strong>the</strong> entry <strong>of</strong> oxygen into <strong>the</strong>aerenchyma system (Armstrong 1964, Teal and Kanwisher1966). Plants were maintained in <strong>the</strong> dark during thismeasurement to prevent <strong>the</strong> release <strong>of</strong> photosyn<strong>the</strong>ticoxygen. Rates <strong>of</strong> oxygen consumption were comparedbetween plants under a 21% O 2 atmosphere and a 100% N 2atmosphere; <strong>the</strong> difference between <strong>the</strong> two flux rates equals<strong>the</strong> amount <strong>of</strong> oxygen transported internally through <strong>the</strong>plant’s aerenchyma system (Lee 2003). Rates <strong>of</strong> internaloxygen transport were standardized to g fresh root weight.Oxygen consumption in <strong>the</strong> dark under 100% N 2 representstotal oxygen demand by <strong>the</strong> plant and was taken to be <strong>the</strong>dark respiration rate (Maricle and Lee 2007).At harvest, root samples were obtained from each plant,flash-frozen in liquid nitrogen, and stored at –80°C.Cytochrome c oxidase (CytOx) and sulfide oxidase (SOx)activities were determined in extracts from root tissuesamples. Roots were ground in liquid nitrogen and coldextraction buffer was added at 2 milliliters per gram (2 mLg -1 ) (Maxwell and Bateman 1967). This mixture washomogenized with a mortar and pestle, filtered throughMiracloth (Calbiochem; San Diego, CA), and centrifuged at1,000 g for 20 minutes at 4°C. The supernatant was used inCytOx and SOx assays. Alcohol dehydrogenase (ADH) wasextracted from root tissue samples after John and Greenway(1976). Roots were ground in liquid nitrogen, and coldextraction buffer was added at 5 mL g -1 . The resultingmixture was homogenized with a mortar and pestle, filteredthrough Miracloth, and centrifuged at 10,000 g for 10 min at4°C. This supernatant was used in ADH assays. All enzymeassays were performed spectrophotometrically at 25°C(Maricle et al. 2006).CytOx activity was determined as <strong>the</strong> rate <strong>of</strong>cytochrome c oxidation, measured as a decrease inabsorbance at 550 nanometers (nm) (Smith 1955). Rates <strong>of</strong>CytOx activity were corrected for background rates <strong>of</strong>cytochrome c oxidation, <strong>the</strong>n standardized to g fresh rootweight. ADH activity was assayed spectrophotometrically in<strong>the</strong> ethanol-forming direction (John and Greenway 1976).Enzyme activity was determined as <strong>the</strong> rate <strong>of</strong> NADHoxidation, measured as a decrease in absorbance at 340 nm.Rates <strong>of</strong> NADH oxidation in <strong>the</strong> presence <strong>of</strong> acetaldehydewere corrected for background rates <strong>of</strong> ethanol formation,<strong>the</strong>n standardized to g fresh root weight (Maricle et al.2006).A colorimetric method was developed to measure <strong>the</strong>activity <strong>of</strong> sulfide oxidation processes. 50 microliter (μL)aliquots <strong>of</strong> extract were added to a series <strong>of</strong> 1 mL buffersolutions <strong>of</strong> 100 μM Na 2 S. 40 μL <strong>of</strong> Cline reagent (Cline1969) was added to <strong>the</strong> solutions after 0, 10, and 20 min todetermine <strong>the</strong> amount <strong>of</strong> sulfide present. Background rates<strong>of</strong> sulfide oxidation were measured by adding 50 μLphosphate buffer instead <strong>of</strong> enzyme extract to a series <strong>of</strong>tubes containing 100 μM Na 2 S as described above. SOxactivity was measured as a decrease in sulfide concentrationover time. Total rates <strong>of</strong> SOx activity were corrected forbackground rates <strong>of</strong> spontaneous sulfide oxidation, <strong>the</strong>nstandardized to g fresh root weight. Rates <strong>of</strong> nonenzymaticsulfide oxidation were determined using 50 μL aliquots <strong>of</strong>boiled enzyme extract. Enzymatic rates <strong>of</strong> sulfide oxidationwere calculated from <strong>the</strong> difference between <strong>the</strong> rates <strong>of</strong>total sulfide oxidation and nonenzymatic sulfide oxidation(Maricle et al. 2006).RESULTS AND DISCUSSIONSoil waterlogging is <strong>the</strong> most common cause <strong>of</strong> plantoxygen deficiency (Vartapetian and Jackson 1997). Impacts<strong>of</strong> flooding on plant productivity can also have significantimpacts on commodity crops. Excessive rains in <strong>the</strong> spring<strong>of</strong> 1993 resulted in a 33% reduction in Midwest cropproduction (Bray et al. 2000). Despite <strong>the</strong>se kinds <strong>of</strong>economic losses, many observers may have overlooked <strong>the</strong>cattails and o<strong>the</strong>r wetland plants flourishing in nearbyflooded ditches. Differences in flooding tolerance have longbeen recognized between plant species, but <strong>the</strong> specificphysiology governing <strong>the</strong> differences has remained largelyunknown.Internal oxygen transport is <strong>of</strong>ten regarded to be animportant factor conferring plant success in waterloggedareas, and <strong>the</strong>refore is thought to be important in estuarinezonation (e.g., Gleason and Zieman 1981, Bertness 1991).The oxygen transport rates measured in this study exhibited-49-
Chapter 1: Spartina Biology<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaFig. 2. (a.) Internal oxygen transport rates, and (b.) root respiration rates(μmol g -1 h -1 ) <strong>of</strong> Spartina and Distichlis grown under flooded soiltreatments. Shown is <strong>the</strong> mean <strong>of</strong> 5-14 plants ± SE. Species are labeled asfollows: S. alt = Spartina alterniflora, S. ang = S. anglica, S. den = S.densiflora, Dist. = Distichlis spicata, S. pat = S. patens.a variability among individuals, with some apparentdifferences between species. The highest rates <strong>of</strong> transportwere exhibited by S. anglica, with moderate to low rates inall o<strong>the</strong>r species (Fig. 2a). Compared to <strong>the</strong> o<strong>the</strong>r species inthis study, S. anglica showed <strong>the</strong> greatest ability to transportoxygen (analysis <strong>of</strong> variance [ANOVA], p
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FORWARD & ACKNOWLEDGEMENTSThe <stro
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TABLE OF CONTENTSForward & Acknowle
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Community Spartina Education and St
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