Photosynthesis of birch genotypes (Betula L.) under varied irradiance and CO2 concentration

摘要

Net CO2 assimilation (A) of four birch genotypes (Betula nigra L. 'Cully', B. papyrifera Marsh., B. alleghaniensis Britton, and B. davurica Pall.) was studied under varied photosynthetic photon flux density (PPFD) and CO2 concentrations (CO2) as indicators to study their shade tolerance and potential for growth enhancement using CO2 enrichment. Effect of water-deficit stress on assimilation under varied PPFD and (CO2) was also investigated for B. papyrifera. The light saturation point at 350 ppm (CO2) for the four genotypes varied from 743 to 1576 mu mol(.)m(-2.)s(-1) photon, and the CO2 saturation point at 1300 mu mol(.)m(-2.)s(-1) photon varied from 767 to 1251 ppm. Light-saturated assimilation ranged from 10.4 mu mol(.)m(-2.)s(-1) in B. alleghaniensis to 13.1 mu mol(.)m(-2.)s(-1) in B. davurica. CO2-saturated A ranged from 18.8 mu mol(.)m(-2.)s(-1) in B. nigra 'Cully' to 33.3 mu mol(.)m(-2.)s(-1) in B. davurica. Water-deficit stress significantly reduced the light saturation point to 366 mu mol photon m(-2.)s(-1) but increased the CO2 saturation point in B. papyrifera. Carboxylation efficiency was reduced 46% and quantum efficiency was reduced 30% by water-deficit stress in B. papyrifera.