Seed dormancy and germination ecology of two alpine Incarvillea species from the Qinghai-Xizang Plateau

This study investigated seed dormancy and germination ecology in two perennial alpine herbs endemic to the Qinghai-Xizang Plateau (QXP), Incarvillea forrestii and I. compacta . We determined how gibberellic acid (GA 3 ), dry after-ripening (DAR) and cold-wet stratification (CS) treatments affect seed germination at three alternating (5/1, 15/5 and 25/15°C) temperatures under light and dark conditions. Seeds of both species possessed a fully-developed embryo and water-permeable seed coats. Freshly dispersed seeds germinated only at higher temperatures (ca. 90% at 25/15°C in light), with germination strongly inhibited at lower temperatures and under dark conditions. GA 3 significantly increased the germination of fresh seeds in both species at 15/5 and 25/15°C, though no promotive effect was observed at 5/1°C. DAR and CS for six months effectively released dormancy, significantly increasing germination percentage and/or reducing mean germination time (MGT) in both light and dark conditions, especially at lower temperature (15/5°C). Dormancy-breaking treatments widened the temperature range for germination from high to low, and also significantly reduced the light requirement for germination. Thus, mature seeds of the two Incarvillea species have (conditional) Type-2 non-deep physiological dormancy. Nondormant seeds germinated rapidly at spring temperature (15/5°C) in both light and dark, enabling immediate germination after snowmelt at the start of the short growing season. The study provides critical insights into the ecological adaptation and diversification of Incarvillea species in the QXP region.