Proceedings of the Third International Conference on Invasive ...

Chapter 1: Spartina Biology<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive Spartina<strong>the</strong> ratio <strong>of</strong> internal to atmospheric CO 2 concentration (c i /c a ).A CO 2 analyzer (Li-Cor 6251; Lincoln, Nebraska) was used tomeasure leaf photosyn<strong>the</strong>tic carbon uptake. Simultaneousmeasures <strong>of</strong> chlorophyll fluorescence (Walz PAM 101;Effeltrich, Germany) allowed calculations <strong>of</strong> grossphotosyn<strong>the</strong>tic rates <strong>of</strong> O 2 evolution. Light-response curveswere generated for PPFD <strong>of</strong> 0-1100 μmol m -2 s -1 . A 20-minutedark period was allowed before measuring F V /F M at 0 μmolm -2 s -1 . The initial slope <strong>of</strong> each plant’s light-response curve(under limiting light) was taken to be <strong>the</strong> quantum efficiency<strong>of</strong> CO 2 fixation or O 2 evolution (Genty et al. 1989).Light-response curves were compared between speciesand treatments using repeated measures analysis <strong>of</strong>covariance (ANCOVAR). Parameters like quantumefficiency, c i /c a , F V /F M , and NPQ were compared betweenspecies and treatments using analysis <strong>of</strong> variance (ANOVA).Treatments were blocked by tubs in all analyses.RESULTS AND DISCUSSIONMaximum rates <strong>of</strong> gross photosyn<strong>the</strong>sis (rates <strong>of</strong> O 2evolution) were quite high in this study (Fig. 1), consistentwith productivity data presented by Long and Woolhouse(1979) for Spartina species. There were no significantdifferences in gross photosyn<strong>the</strong>sis rates between species,treatment, or <strong>the</strong>ir interactions (ANCOVAR, p≥0.439).Maximum quantum efficiencies <strong>of</strong> O 2 evolution,measured under limiting light, were not significantlydecreased by salinity in any species (ANOVA, p≥0.107;Table 1). Values for gross quantum efficiencies in Spartinaand Distichlis were slightly higher than previously publishednet quantum efficiency measures for C 4 monocots.Values for quantum efficiencies <strong>of</strong> CO 2 fixation wereslightly lower than gross quantum efficiencies (Table 1) andwere similar to those reported by Ehleringer and Pearcy(1983) for C 4 monocots. Quantum efficiencies <strong>of</strong> CO 2fixation decreased in S. alterniflora and S. patens withincreased salinity (ANOVA, p≤0.058), but not in any o<strong>the</strong>rFig. 1. Light-response curves showing gross photosyn<strong>the</strong>sis rates (μmolO 2 evolved m -2 s -1 ) <strong>of</strong> Spartina and Distichlis plants in flooded or drainedsoil conditions and salt up to 30‰. Points are means <strong>of</strong> 3-23 plants ± SD.species (ANOVA, p≥0.161).There were large differences between gross and netphotosyn<strong>the</strong>sis rates in most species (Table 2). This resulted ina surplus <strong>of</strong> harvested light energy not used in CO 2 fixation.This energy must be dissipated in order to prevent damage tophotosyn<strong>the</strong>tic reaction centers. Net rates <strong>of</strong> photosyn<strong>the</strong>siswere lower in 30‰ salt compared to 0‰ salt in S. patens, S.alterniflora, and D. spicata (ANOVA, p≤0.063), but not in S.anglica or S. densiflora (ANOVA, p≥0.624).Maintaining gross photosyn<strong>the</strong>sis rates (as measured byfluorescence yield) in <strong>the</strong> light while rates <strong>of</strong> CO 2 fixationdecrease with increasing salinity indicates additionalTable 1. Photosyn<strong>the</strong>sis data collected for high- and low-salinity, flooded-treatment plants in <strong>the</strong> gas-exchange system. Shown is <strong>the</strong> net quantum efficiency <strong>of</strong> CO 2fixation, <strong>the</strong> gross quantum efficiency <strong>of</strong> O 2 evolution, <strong>the</strong> maximum amount <strong>of</strong> nonphotochemical quenching and c i/c a values at 1100 μmol m -2 s -1 , and <strong>the</strong> maximumF V/F M ratio <strong>of</strong> dark-adapted plants. The mean ± SD (n) is given for each species/treatment combination.Species TreatmentsalinityNet QE(CO 2 photon -1 )Gross QE(O 2 photon -1 )Max NPQ(unitless)c i/c a(unitless)Max F V/F M(unitless)S. alterniflora 0‰ 0.065 ± 0.020 (3) 0.066 ± 0.010 (3) 1.99 ± 0.24 (3) 0.53 ± 0.10 (3) 0.74 ± 0.01 (3)30‰ 0.026 ± 0.016 (3) 0.046 ± 0.010 (3) 1.80 ± 0.36 (3) 0.60 ± 0.15 (3) 0.67 ± 0.08 (3)S. anglica 0‰ 0.025 ± 0.018 (4) 0.049 ± 0.009 (4) 1.64 ± 0.33 (4) 0.61 ± 0.11 (4) 0.72 ± 0.04 (4)30‰ 0.027 ± 0.021 (4) 0.056 ± 0.009 (4) 1.63 ± 0.50 (4) 0.41 ± 0.08 (4) 0.72 ± 0.03 (4)S. densiflora 0‰ 0.049 ± 0.048 (4) 0.056 ± 0.014 (4) 1.78 ± 0.24 (4) 0.57 ± 0.17 (4) 0.74 ± 0.01 (4)30‰ 0.034 ± 0.025 (4) 0.063 ± 0.006 (4) 1.44 ± 0.12 (4) 0.35 ± 0.14 (4) 0.73 ± 0.01 (4)S. patens 0‰ 0.067 ± 0.018 (3) 0.068 ± 0.003 (3) 1.19 ± 0.08 (3) 0.56 ± 0.14 (3) 0.71 ± 0.01 (3)30‰ 0.033 ± 0.022 (3) 0.057 ± 0.007 (3) 1.70 ± 1.16 (3) 0.53 ± 0.19 (3) 0.72 ± 0.01 (3)D. spicata 0‰ 0.038 ± 0.002 (3) 0.050 ± 0.014 (3) 0.79 ± 0.23 (3) 0.53 ± 0.04 (3) 0.60 ± 0.10 (3)30‰ 0.023 ± 0.015 (4) 0.057 ± 0.006 (4) 1.39 ± 0.37 (4) 0.53 ± 0.19 (3) 0.69 ± 0.04 (4)-56-