NET PHOTOSYNTHESIS OF BLACK LOCUST SEEDLINGS IN RESPONSE TO IRRADIANCE, TEMPERATURE AND CO2

The responses of rates of net photosynthesis (P(N)) to photosynthetic photon fluence rate (I), leaf temperature and CO2 Were studied in half -sib families of greenhouse and field grown black locust (Robinia pseu doacacia L.) seedlings. The response Of P(N) to I was similar in both greenhouse and field grown seedlings, except the quantum yields were l ower in the field grown seedlings. The saturating I was as low as 600 mumol m-2 s-1 in some seedlings but did not saturate at 1900 mumol m-2 s-1 in others. The optimum temperature for P(N) in field grown seedli ngs was slightly lower than greenhouse grown seedlings. P(N) increased rapidly with increased CO2 up to 350 mumol mol-1, but beyond 500 mumo l mol-1 the increase was gradual in some families, On average, stomata represented only 23 % of the limitation to P(N) with no differences b etween families observed. Family x I, family x temperature and family x CO2 were not significant for P(N).