Salinity and temperature influencing seed germination of Mediterranean Aleppo pine (Pinus halepensis Mill.): an ecological adaptation to saline environments

Abstract

In Mediterranean basin, Pinus halepensis Mill. is the dominant conifer used in afforestation and landscape projects. The ecological, aesthetic and commercial benefits make this conifer a precious tree for both woody production and land rehabilitation. Nevertheless, detailed studies on the adaptation of this tree to abiotic environmental constraints in the Mediterranean areas remain limited up until now. Therefore, laboratory experiments were conducted to assess the effects of the interactive impact of temperatures and salinity on the germinability potential of P. halepensis seeds. The cones of P. halepensis used in this experiment were harvested from the Gotaïa forest at Djelfa province, Algeria. The seeds were removed from their cones and surface-sterilized by soaking for five min in 10% NaClO. Seeds were germinated at three temperature regimes (10–20 °C, 15–25 °C and 20–30 °C) and four levels of salinity (0, 50, 100, and 150 mM NaCl) at photoperiodic lighting (16 h of light : 8 h of dark). For each treatment 04 replicates of 25 seeds were placed in Petri dish with 5 ml of test solutions. A completely randomized design (CRD) was used for the experiment. Results revealed that the uppermost germinability was recorded in distilled H2O and the progressive enhancement of NaCl significantly (P < 0.001) suppressed germination. At 15–25 °C (dark : light thermoperiod), P. halepensis seeds showed approximately 90% of germination at 0 mM NaCl. However less germination percentage (GP) was obtained at 10–20 °C and 20–30 °C. Values of Timson’s index were also suppressed significantly (P < 0.001) with an increase under salt stress at all thermoperiods but at least at 15–25 °C. These funding suggest that seeding of P. halepensis may be an effective path for rehabilitation of degraded lands where salinity and drought are major features of the arid ecosystems. Yet, this conclusion still needs verification by field experiments. Key words: Pinus halepensis; arid zones; sowing dates; afforestation; salt tolerance