Effects of light and temperature parameters on net photosynthetic carbon dioxide fixation by whole plants of five lupin species (Lupinus albus L., Lupinus angustifolius L., Lupinus luteus L., Lupinus mutabilis Sweet. and Lupinus polyphyllus Lindl.)

Net photosynthetic CO, uptake by whole plants of five lupin species (Lupinus albus L., Lupinus angustifolius L., Lupinus luteus L., Lupinus mutabilis Sweet. and Lupinus polyphyllus Lindl.) was measured and modelled in laboratory conditions by an infrared gas analyser at six levels of photosynthetic photon flux density (PPFD: 0, 176, 352, 528, 704 and 880 mumol m(-2) s(-1))and four temperatures (5, 17, 22 and 29degreesC). Measured net photosynthetic CO2 uptake for all lupin species in all experimental conditions was 10.34 mg CO2 dm(-2) h(-1) with a standard deviation (+/-SD) of 10.24 and standard error (SE) of 0.71 mg CO2 dm(-2) h(-1). The mean value of net photosynthetic CO2 uptake in all experimental conditions was 9.86 for L. albus, 12.71 for L. angustifolius, 10.92 for L. luteus, 7.77 for L. mutabilis and 10.04 CO2 dm(-2) h(-1) for L. polyphyullus . A hyperbolic equation was formulated to illustrate the relationship between light and temperature as independent variables and net photosynthetic CO2 fixation as the dependent variables (r(2) = 0.91). At temperatures from 17.1 to 20.1degreesC and level of PPFD of 880 mumol m(-2) s(-1) the maximal net photosynthesis varied from 25.0 to 27.0 mg CO2 dm(-2) h(-1) depending on species (25.0 for L. albus, 26.0 for L. angustifolius and L. luteus, 27.0 for L. mutabilis and 26.7 for L. polyphyllus). The differences in net photosynthetic CO2 fixation were more clearly observed at low temperatures (9.2-12.5degreesC) and at a low level of PPFD (220 mumol m(-2) s(-1)), and varied from 9.1 to 12.2 mg CO2 dm(-2) h(-1)(L. albus 9.1, L. angustifolius 10.6, L. luteus 11.0, L. mutabilis 12.2 and L. polyphyllus 12.0). It is concluded that the response of net photosynthetic CO, fixation to parameters of light and temperature can be used in the ecological description of lupin species diversity. Future studies are needed to clarify this response at both the cellular and molecular levels.