Eco-Adaptability Of Mucilaginous Seeds Germination In Ephemeral Alyssum Minus

Alyssum minus (L.) Rothm. is an annual ephemeral Brassicaceous species that grows only in grasslands and alpine meadows of the Tianshan mountains and in shrublands of the northwestern part of the Junggar Basin of Xinjiang Province in China. Its seeds produce a large amount of mucilage when imbibed in water. Strategies of seed germination are various and produce autumn-and spring-germinating plants. The primary aim of this study was to explore the role of mucilage in seed dispersal, settlement onto the soil surface and germination, and effect of water on germination time and life-history traits of this species. The main results are as follows:(1) The width of imbibed seeds with mucilage was greater than three times that of seeds without mucilage, and the mass of the mucilage increased167times after imbibition. Expanded dry mucilage significantly increased wind dispersal of seeds. Floating time on water was greatest for seeds without mucilage, and adherence of soil particles to seeds was greater for seeds with mucilage than for those without mucilage. Mucilage increased the rate of water uptake and decreased the rate of water loss. It also significantly decreased germination of0-and4-week-old seeds. GA3promoted germination of0-and4-week-old seeds with and without mucilage, but its effect depended on seed age and incubation temperature. Seeds with mucilage that were subjected to water stress during imbibition and/or incubation germinated faster than those without mucilage. Presence of mucilage on seeds during imbibition significantly increased germination percentages under increased water stress, a first report of this phenomenon.(2) Seeds that were watered germinated2weeks after sowing, but seeds that were not watered did not germinate until after heavy rainfall appeared. This result suggests that lack of moisture is an important factor that restricts the germination of non-dormant seeds. Non-watered autumn-and spring-germinating plants wer earlier to flower, fruit, mature seeds and senesce than watered plants. The life cycle of autumn-germinating plants was longer, and they were earlier to senesce than spring-germinating plants under the same water treatement. Watered autumn-germinating plants had the greatest plant height at maturity, number of branches, length of branches and fruits, and seed production followed by non-watered autumn-germinating plants, and then watered spring-germinating plants, with non-watered spring-germinating plants having the least. Moreover, autumn-germinating plants had greater dry mass than spring-germinating plants under all treatments. Watered spring-germinating plants allocation to roots and leaves showed that had greater than watered autumn-germinating plants, and non-watered autumn-germinating plants greater allocation to roots and leaves than watered autumn-germinating plants. Watered autumn-germinating plants had greater allocation to fruits than watered spring-germinating plants, and watered autumn-germinating plants had greater allocation to fruits than non-watered autumn-germinating plants.Mucilage of A. minus presumably plays an important ecological role in seed dispersal, seed adhesion to the soil, thereby preventing removal by water and predators; seed hydration via increasing the surface area contact with the substrate; and acting as a water reservoir for germination, especially under conditions of water stress. Some seeds had the ability to break dormancy and germinate in autumn in their natural habitat, but seeds did not germinate or germinated late when they received low rainfall. Moisture strongly influenced seed germination time which inturn influenced life-history traits. Therefore changes in rainfall that will accompany climate change are espected to have significant effects on germination time and life-history traits. Knowledge of functional traits, such as mucilage, that influence germination and lifehistories in unpredictable desert environments is valuable for predicting how different plants may respond to climate change.