Seed dormancy, germination and soil seed bank of Lamiophlomis rotata and Marmoritis complanatum (Labiatae), two endemic species from Himalaya–Hengduan Mountains

Abstract

Seed dormancy and germination characteristics are important factors determining plant reproductive success. In this study, we aimed to explore the characteristics of seed dormancy and germination of two endemic Labiatae species (Lamiophlomis rotata and Marmoritis complanatum) in the Himalaya–Hengduan Mountains. Germination was first tested in the light using freshly matured seeds at 25/15 and 15/5°C, and then again after dry after-ripening. Dried seeds were incubated in the light at a range of constant temperatures (1–35°C). The effects of dark and GA3 on germination were tested at several different temperatures. Base temperature (Tb) and thermal times for 50% final germination (θ50) were calculated. Seeds were also buried at the collection site to test seed persistence in the soil. Increased final germination after dry after-ripening indicated that the seeds of the two species exhibited non-deep physiological dormancy; however, they exhibited different germination characteristics and soil seed bank types. In L. rotata, GA3 only promoted germination at 5°C, producing no significant effect at other temperatures. Dark conditions decreased germination significantly at all temperatures. Tb and θ50 values were 0.6 and 82.7°C d. The soil seed bank of this species was classified as persistent. In M. complanatum, GA3 significantly promoted germination at all temperatures except 15°C. Dark conditions depressed germination significantly at warmer temperatures (20 and 25°C) but had no effect at lower temperatures. Tb and θ50 values were 0.1 and 92.3°C d. The soil seed bank was classified as transient. Our results suggest that the seed dormancy and germination of the two co-existing species share some commonalities but there are also species-specific adaptations to the harsh alpine environment.