In semiarid ecosystems, many plant species are tolerant to drought. However, increased aridity as a result of climatic change could modify the capacity of germination and establishment. Hypothesis: Under drought conditions, small-seeded species will tend to germinate in higher proportions than large-seeded species because the former have larger surface-to-volume ratio, allowing for more rapid water uptake. Study species: Ageratina espinosarum, Flourensia resinosa, Montanoa tomentosa and

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... rma glutinosum (Asteraceae), Dalea bicolor, Eysenhardtia polystachya and Mimosa pringlei (Fabacecae). Study site: Hidalgo, Mexico. September 2015. Methods: We evaluated the effect of five water potential treatments on seed germination. Four dishes (replicates), each with 25 seeds, were used in each treatment. Seeds of each species were weighed and the relationship between seed germination under water stress and seed size was obtained. Results: Germination decreased as water potential was reduced; almost no seeds germinated at -0.8 MPa. The least sensitive species was Eysenhardtia polystachya, whose germination reached 35 % at -0.6 MPa. A positive relationship was found between seed size and germination proportion under water stress. Conclusions: Contrary to expectation, germination was higher in the large-seeded species in all drought treatments, suggesting that large seeds may have a greater capacity to retain water in dry environments.