impact of drought stress on photosynthetic response of some pear species

To investigate photosynthetic response of some pear (pyrus spp.) species to drought stress, a pot experiment was conducted using as factorial experiment based on completely randomized design (crd) with three replication under greenhouse condition. the factors included five pear species including: p. biossieriana, p. communis, p. glabra, p. salicifolia and p. syriaca and three levels of drought stress [(100%, 60% and 30% of field capacity (fc)]. according to the obtained results, different levels of drought stress significantly restricted morphological and physiological responses in all studied species. increasing drought stress intensity reduced leaf relative water content (rwc), net photosynthetic rate, stomatal conductance, transpiration rate and intercellular carbon dioxide concentration when compared to their values in control plants. however, root/shoot dry weight ratio, specific leaf weight and stomatal density per unit of area were increased. in p. glabra exposed to severe stress (30% of fc), the values of root/shoot dry weigh ratio (0.85 g), specific leaf weight (23 mg cm^-2), stomata density per unit of area, relative water content (73%) and net photosynthetic rate (3.9 µmol co2 m^-2 s^-1) were significantly higher than the other species. p. syriaca, p. salicifolia, p. biossieriana and p. communis were placed in the next ranks, respectively based on their response to drought. in conclusion, p. glabra is reported as a more effective species in mitigating the adverse effects of drought by boosting its protective mechanisms than the other pear species.