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 mu mol m(-2) s(-1) to 1.21 x 10(3) mu mol m(-2) s(-1) at temperatures of 5, 15, 18, 25 and 31 degrees C. NPP was 0.0 mg CO2 gDM(-1) h(-1) a t a PPFD of 1.1 x 10(2) mu mol m(-2) s(-1) and temperature of 5 degree s C. A PPFD of 1.21 x 10(3) mu mol m(-2) s(-1) produced 4.44 mg CO2 gD M(-1) h(-1) at 5 degrees C and 7.15 mg CO2 gDM(-1) h(-1) at 15 degrees C, but 5.57 mg CO2 gDM(-1) h(-1) at 25 degrees C. Average night respi ration was 2.24 mg CO2 gDM(-1) h(-1). The highest average NPP under ex perimental conditions was 8.56 mg CO2 gDM(-1) h(-1) with a PPFD of 1.1 x 10(3) mu mol m(-2) s(-1) at 31 degrees C. An equation was developed for fodder galega to illustrate the relationship between photosynthet ic photon flux density and temperature as independent variables and NP P as the dependent variable. The optimum temperatures for NPP of fodde r galega were from 12.5 to 32 degrees C in minimum light conditions of 7.26 x 10(2) mu mol m(-2) s(-1) and a maximum night-time temperature of 15 degrees C. The potential maximum NPP was about 9 mg CO2 gDM(-1) h(-1) and occurred at a temperature of 23 degrees C and a PPFD of 1.21 x 10(3) mu mol m(-2) s(-1). Fodder galega required increased illumina tion at the beginning of the vegetation period.