Effect of Polyethylene glycol, temperature, and stratification in thirty plant species: Implications for conservation and management

Seed ecology is a fundamental view of a population's regenerative potential and under climate change needs investigation for proper management and conservation of plant populations. In the Mediterranean basin extreme rainfall variability is expected to prevail during the next decades. The aim of the study is to investigate the germination potential of thirty plant species by placing their seeds under gradients of water potentials with the use of polyethylene glycol, a polymer used to mimic water stress in seeds to assess their adaptive potential. We applied three different osmotic potentials (-0.03 MPa , -0.50 MPa, -1.56 MPa) using PEG6000 in seeds from thirty different plant species. Prior PEG treatment seeds grouped to non-stratified and stratified ones at +2°C for 1 month. Seeds were then germinated under either constant +21°C or alternate +25°C/+15°C temperature with 12-hours photoperiod. Germination was affected by PEG level, stratification and temperature which acted either independently or in combination, and the response to those factors was species specific. Most species that PEG had affected their germination, responded positively in water stress at -0.5 MPa and some of them further increased their seed germination under -1.56 MPa. However, in species where PEG had no effect, their germination response was driven by the other two factors either independently or in combination. Finally, there were also species that presented low germination, unaffected by the studied factors. The present study demonstrates the ability of several Mediterranean species to germinate under various levels of water stress and can be applied to species management and conservation strategies.