Effects of light and temperature on net primary productivity of fodder galega (Galega orientalis Lam.)

The effects of light and temperature on the net primary productivity (NPP) of fodder galega (G. orientalis Lam.) were studied in two series of experiments. NPP was determined under laboratory conditions using a stepwise change in photosynthetic photon flux density (PPFD) from 0.0 μmol m −2 s −1 to 1.21 × 10 3 μmol m −2 s −1 at temperatures of 5, 15, 18, 25 and 31°C. NPP was 0.0 mg CO 2 gDM −1 h −1 at a PPFD of 1.1 × 10 2 μmol m −2 s −1 and temperature of 5°C. A PPFD of 1.21 × 10 3 μmol m −2 s −1 produced 4.44 mg CO 2 gDM −1 h −1 at 5°C and 7.15 mg CO 2 gDM −1 h −1 at 15°C, but 5.57 mg CO 2 gDM −1 h −1 at 25°C. Average night respiration was 2.24 mg CO 2 gDM −1 h −1 . The highest average NPP under experimental conditions was 8.56 mg CO 2 gDM −1 h −1 with a PPFD of 1.1 × 10 3 μmol m −2 s −1 at 31°C. An equation was developed for fodder galega to illustrate the relationship between photosynthetic photon flux density and temperature as independent variables and NPP as the dependent variable. The optimum temperatures for NPP of fodder galega were from 12.5 to 32°C in minimum light conditions of 7.26 × 10 2 μmol m −2 s −1 and a maximum night-time temperature of 15°C. The potential maximum NPP was about 9 mg CO 2 gDM −1 h −1 and occurred at a temperature of 23°C and a PPFD of 1.21 × 10 3 μmol m −2 s −1 Fodder galega required increased illumination at the beginning of the vegetation period.