Tree growth and leaf gas exchange variability of three Mediterranean Pinus spp. growing in a common garden in Northeastern Tunisia

A dendrochronological approach and gas exchange techniques were used to study the adaptation of Pinus halepensis, Pinus pinea, and Pinus brutia growing in a 47-year-old common garden experiment to the local subhumid climate in Northeastern Tunisia. P. pinea showed the highest survival rate, the greatest height, the widest diameter at breast height, and the largest specific leaf area. The lowest values were recorded for P. halepensis. Ring width data showed that P. pinea had the highest radial growth, which was correlated to the lowest mean sensitivity and the first-order autocorrelation coefficient. The highest values of the abovementioned parameters were recorded for P. halepensis. CO2 response curves of net leaf photosynthesis were used to directly calculate the main photosynthetic parameters, including the CO2-saturated net photosynthesis rate, stomatal limitation, and carboxylation efficiency. At the natural ambient CO2 concentration, P. brutia presented the lowest net photosynthesis, P. pinea exhibited the highest water-use efficiency, and the highest stomatal conductance was recorded for P. halepensis. Furthermore, at a high concentration of CO2, the highest stomatal limitation was recorded for P. brutia, which may partially explain why it presented the lowest net CO2-saturated photosynthesis rate; the highest net CO2-saturated photosynthesis rate was observed for P. halepensis. The response of the growth pattern to the climate was found to depend on the species. P. pinea showed the highest radial growth and water-use efficiency, implying that this species is the best suited of the three species investigated to the pedoclimatic conditions in the studied area.