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  • 1
    Electronic Resource
    Electronic Resource
    Photosynthesis of Littorella uniflora grown under two PAR regimes: C3 and CAM gas exchange and the regulation of internal CO2 and O2 concentrations (1990)
    Springer
    Oecologia 85 (1990), S. 128-136 
    Details
    ISSN: 1432-1939
    Keywords: Littorella uniflora ; Gas exchange ; Crassulacean acid metabolism ; Lacunal CO2 and O2 concentrations ; PAR acclimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The submersed aquatic macrophyte Littorella uniflora was grown under 50 and 300 μmol m−2 s−1 photosynthetically active radiation (PAR) (low and high PAR regimes) but identical sediment CO2 supply (1.0 mol m−3). The interactions between plant morphology, whole plant CO2 and O2 exchange, CAM activity, [CO2] i and [O2] i have been investigated in comparison with in vitro CO2 and PAR response characteristics (using 1 mm leaf sections). In terms of morphology, high-PAR-grown plants were smaller and leaves contained less chlorophyll, although root growth was proportionally larger. Gas exchange fluxes over roots and shoots of intact plants were similar in direction under the two PAR regimes, with the majority of CO2 uptake via the roots. Photosynthetic O2 evolution from intact plants was greater in high-PAR-grown L. uniflora (2.18 compared with 1.49 μmol O2g−1 fresh weight h−1 for the low PAR regime). Although net daytime CO2 uptake was similar for both PAR regimes (0.79 and 0.75 μmol g−1 fwt h−1), net dark CO2 uptake was at a higher rate (0.92 compared with 0.52 μmol CO2 g−1 fwt h−1), and dark fixation (as malic acid) was threefold greater in high PAR plants (ΔH+ 117 compared with 42 μmol H+ g−1 fwt). Comparison of dark CO2 uptake with dark fixation suggested that much of the CO2 fixed at night and regenerated during the day may be respiratory in origin (60% low PAR plants, 71% high PAR plants). Regeneration of CO2 from CAM could account for 62% of daytime CO2 supply in low PAR plants and 81% in high PAR plants. [CO2] i values (ranging from 0.42 to 1.03 mol m−3) were close to or above the concentration required to saturate photosynthesis in vitro (0.5 mol m−3) under both PAR regimes, and combined with the low [O2] i (2.6–4.3 mol m−3) should have suppressed photorespiration. However, PAR inside leaves would have been well below the in vitro light saturation requirement (850–1000 μmol m−2 s−1 for both treatments). Thus PAR rather than CO2 supply appeared to limit photosynthesis even in high PAR grown plants, and CAM appears to have an important role in the regulation of CO2 supply for photosynthesis in response to variation in light regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317353
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  • 2
    Electronic Resource
    Electronic Resource
    The impact of NO inf3 sup− loading on the freshwater macrophyte Littorella uniflora: N utilization strategy in a slow-growing species from oligotrophic habitats (1994)
    Springer
    Oecologia 100 (1994), S. 368-378 
    Details
    ISSN: 1432-1939
    Keywords: Littorella uniflora ; Eutrophication ; Nitrogen assimilation ; Storage ; Nitrogen use efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The decline and disappearance of Littorella uniflora from oligotrophic waters which have become eutrophic has been associated with shading or reduced CO2 supply. However NO inf3 sup− concentrations can reach very high levels (100–2000 mmol m−3 compared with 〈1–3 in oligotrophic habitats). To investigate the impact of NO inf3 sup− loading alone, plants were grown under three NO inf3 sup− regimes (very low, near-natural and high). The interactive effects of NO inf3 sup− and photon flux density (low and high regimes) on N assimilation and accumulation, CO2 concentrating mechanisms, C3 photosynthesis and growth were also examined. The results were unexpected. Increased NO inf3 sup− supply had very little effect on photosynthetic capacity, crassulacean acid metabolism (CAM) or lacunal CO2 concentrations ([CO2]i), although there was considerable plasticity with respect to light regime. In contrast, increased NO inf3 sup− supply resulted in a marked accumulation of NO inf3 sup− , free amino acids and soluble protein in shoots and roots (up to 25 mol m−3, 30 mol m−3 and 9 mg g−1 fresh weight respectively in roots), while fresh weight and relative growth rate were reduced. Total N content even under the very low NO inf3 sup− regime (1.6–2.3%) was mid-range for aquatic and terrestrial species (and 3.1–4.3% under the high NO inf3 sup− regime). These findings, together with field data, suggest that L. uniflora is not growth limited by low NO inf3 sup− supply in natural oligotophic habitats, due not to an efficient photosynthetic nitrogen use but to a slow growth rate, a low N requirement and to the use of storage to avoid N stress. However the increased NO inf3 sup− concentrations in eutrophic environments seem likely have detrimental effects on the long-term survival of L. uniflora, possibly as a consequence of N accumulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317857
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