Effects of water stress and smoke on germination of Mediterranean shrubs with hard or soft coat seeds

Abstract

Mediterranean shrublands are water-limited and fire-prone ecosystems. Post-fire seed regeneration occurs under a rainfall regime that is highly variable, with frequent drought periods. It has been shown that smoke can alter germination performance in numerous species, but little is known about its role during germination under water stress. Here, we studied the germination response to water stress and smoke of nine abundant Mediterranean shrubs. Seeds of six species with hard coats (three Cistaceae and three Fabaceae) and three with soft coats (Lamiaceae), exposed or not to smoke, were set to germinate under four levels of water availability (0; − 0.15; − 0.30; − 0.45 MPa). Seeds of hard-coat species were previously mechanically scarified. Onset of germination, final germination and viability were recorded. Water stress reduced final germination in five of the six hard-coat species and in one soft-coat species, delayed the onset of germination in all species and decreased viability in several hard-coat species. Smoke increased final germination (10%) in one soft-coat species, not affecting the rest. Additionally, smoke reduced the onset of germination in one hard- and one soft-coat species. However, there was no interaction between smoke and water stress. Hydrotime modeling of the germination responses confirmed the above findings. In conclusion, the species studied differed in germination sensitivity to water stress, with hard-coat species being more sensitive than soft-coat species. Exposing the seeds to smoke generally did not change this sensitivity.