Drought tolerance during germination depends on light and temperature of incubation in Salsola imbricata, a desert shrub of Arabian deserts

Plant recruitment in desert ecosystems is rare and highly unpredictable due to unfavourable conditions inhibiting germination events. Few studies addressed the impacts of water deficiency, temperature and light on germination of desert shrubs. Here, we assessed the impact of simulated drought (osmotic stress) as simulated by polyethylene glycol (PEG), light and temperature of incubation on seed germination of Salsola imbricata, a leaf succulent perennial shrub of the arid Arabian deserts. Fresh seeds were germinated in different osmotic potentials (0 up to -2.2 MPa PEG) at three temperatures and in two light regimes. In distilled water, germination was significantly greater at higher than at lower temperatures when seeds germinated in light, but the reverse was true in darkness. Both final germination and germination rate index (GRI) decreased gradually with the increase in osmotic stress, but the reduction was more pronounced at higher, compared to lower temperatures. Final germination and GRI decreased from around 70% and 49, respectively, in distilled water at both low and high temperatures to 44% and 39 in -1.4 MPa at low temperatures, but to 5% and 26, respectively, at higher temperatures. At higher temperatures, germination was significantly reduced in darkness, compared to light conditions, for most tested osmotic potentials. Most non-germinated seeds in PEG solutions recovered their germination when transferred to distilled water, indicating positive osmopriming effect for PEG. The temperature specific adaptation to lower osmotic potentials explains the ability of S. imbricata seeds to germinate early in seasons with little rainfalls.