Sensitivity of Chihuahuan Desert cacti to heat and water limitation during germination

Climate change is altering temperature and precipitation regimes in arid regions, yet the germination thresholds of many drought-adapted cacti remain poorly resolved. We evaluated the effects of temperature and water potential on seed germination of five cactus species from the southern Chihuahuan Desert (Mexico): Echinocactus platyacanthus, Ferocactus pilosus, Mammillaria bocasana, Myrtillocactus geometrizans and Stenocereus huastecorum . Seeds were exposed to two constant temperatures (25 and 32°C) and three water potentials (0, −0.2 and −0.4 MPa) under controlled laboratory conditions. Germinability, mean germination time and germination speed responded strongly and species-specifically to thermal and hydric stress. Myrtillocactus geometrizans and S. huastecorum maintained high germination across treatments, indicating broad germination tolerance. In contrast, F. pilosus and E. platyacanthus exhibited sharp declines in germination and delayed germination dynamics under combined heat and drought stress, while M. bocasana was primarily constrained by high temperature. Viability assessments revealed that many ungerminated seeds remained viable, suggesting physiological dormancy. These results indicate that cactus species differ markedly in their germination niches, with important consequences for recruitment under high temperature and drying. Incorporating species-specific germination thresholds and dormancy behaviour into conservation and restoration strategies will be essential for predicting population persistence under climate change.