Adjustment of photosynthetic carbon assimilation to higher growth irradiance in three-year-old seedlings of two Tunisian provenances of Cork Oak (Quercus suber L.)

Three-year-old seedlings of two Tunisian provenances of cork oak (Quercus suber L.) differing in climatic conditions at their geographical origin were subjected to increasing light intensities. Ga’four was the provenance from the driest site and Feija from the wettest site. Low-light adapted seedlings from both provenances were exposed to two light treatments: full sunlight (HL) and low light (LL, 15% sunlight) for 40 days. The CO2-response curve of leaf net photosynthesis (An-Ci curve) established under saturated photon flux density was used to compare photosynthetic parameters between leaves subjected to continuous low light (LL leaves) and leaves transferred from low to high light (HL leaves). Transfer from low to high light significantly increased net photosynthesis (An) and dark respiration (Rd) in Ga’four provenance but not in Feija. After transfer to high irradiance, specific leaf area (SLA) did not change in either provenance. This suggested that the increase in photosynthetic capacity on a leaf area basis in HL leaves of Ga’four provenance was not due to increased leaf thickness. Only the seedlings from the Ga’four provenance were able to acclimate to high light by increasing Vcmax and Jmax.