Effect of temperature and drought stress on germination of Magnolia pugana, an endangered species from western Mexico

Background: Magnolia pugana populations are declining, in addition, it is estimated that precipitation will decrease by up to 10 % and temperatures will increase (2-4 °C) under the most severe climate change scenario, which may affect germination. Hypotheses: The interaction of increased temperature and decreased water potential reduces and delays the germination of Magnolia pugana seeds. Studied species: Magnolia pugana, an endangered species endemic to western Mexico. Study site and dates: Southern Zacatecas and central Jalisco, Mexico. April 2019. Materials and methods: Seed viability was evaluated with tetrazolium test. In addition, the effects of temperature (24, 28, and 37 °C), water potential with PEG 8000 (0, -0.3, -0.6, -0.9, -1.2 MPa) and its interaction on the percentage and mean germination time were analyzed with factorial ANOVA tests. Results: Viability was 80 %. The interactions between temperature and water potential on germination percentage and mean germination time were significant. There was no germination at 37 °C. The highest germination (78 %) was at 24 °C and -0.3 MPa, while the lowest (3 %) was at 28 °C and -0.6 MPa. The control treatment (24 °C and 0 MPa) facilitated germination in a shorter time (23.9 ± 1.5 days). At 28 °C and -0.9 MPa, the mean germination time was slowed by 1.5 times. Conclusions: Magnolia pugana germinability was reduced by the interaction between low water potentials and increased temperature, conditions predicted by future climate change scenarios, therefore its vulnerability to extinction couldincrease.