Investigation On The Reproductive Strategy Of Dimorphic Cleistogamous Viola Tuberifera Endemic To Qinghai-Tibetan Plateau

Reproduction is the basic behavior and process of biological sustainable survival and successful multiply, and also is one of the research for plant life history. By studying plant reproductive strategies in different environments can reveal the ability of plants to adapt to the environment and the reproductive potential in the habitat.Flowering phenology, seed dispersal is closely related to the reproductive success of plants, which plays an important role in maintenance and updating of plant populations. Now, the experimental evidence of the reproductive strategies of cleistogamous breeding system plants is still lacking.Viola tuberifera, a typical dimorphic cleistogamous plant, which endemic to Qinghai-Tibetan Plateau and its eastern neighbour region. It can produce chasmogamous flowers, aerial cleistogamous flowers and subterranean cleistogamous flowers in the same plant, so it is an excellent material to study reproductive adaptation of mixed mating system plants. Therefore, in this paper, we chose Viola tuberifera as materials to investigate the flowering phenology and reproduction characteristics, dispersal characteristics of the seeds of subterranean cleistogamous flowers in different altitudes and habitats, aiming at ascertaining Viola tuberifera which endemic to Qinghai-Tibetan Plateau how to adapt to alpine environment, So as to provide the basis of adaptive evolution of mixed breeding system, particularly typical dimorphic cleistogamous plants. The results showed that:1. Viola tuberifera population chasmogamous flowers blooming on the end of May to late June. Flowering duration was about 12 ~ 15 days. With the increase of altitude, the onset, median flowering date and end date of Viola tuberifera were delayed and flowering amplitudes for the low altitude above the high altitudes. The onset, median flowering date and end date of Viola tuberifera in meadow and mound with enough light were earlier than shrub and forest edge with low light. The flowering amplitudes in meadow and mound were higer than that in shrub and forest edge. Moreover, Viola tuberifera was “centralized flowering mode” in different altitudes and habitats, which may be a selection pressure formed in a variety ofadaptive behavior to their living environment.2. Viola tuberifera can carry out not only sexual propagation but also asexual reproduction. The same plant can produce CH flowers, aerial cleistogamous flowers and subterranean cleistogamous flowers, which can produce three types of seeds. In this three modes of sexual reproduction, the number of flowers was aerial cleistogamous flowers > subterranean cleistogamous flowers > CH flowers; the number of flowers was CH flowers seeds> aerial cleistogamous flowers seeds>subterranean cleistogamous flowers seeds. Viola tuberifera can conduct clonal growth through bulbs, rhizomes, spacers and new bulbs from stolons. However, the remats mainly produced through the new bulbs from stolons, which can effectively avoid the threat to remats from colder3. With the rise of altitude, the number of CH flowers and seeds significantly reduced, but the number of subterranean cleistogamous flowers and seeds was significantly increased. When the altitude was in the range of 2700 ~ 3300 m, the number of aerial cleistogamous flowers and seeds was increased along with the gradually increasing altitude. If the altitude continued to rise, their number significantly reduced. Therefore, the elevation had a certain effect on the sexual and asexual propagation of Viola tuberifera. With the rise of altitude, the investment to CH flowers was gradually reduced, but the investment to CL flowers was gradually strengthened. If the altitude continued to rise, Viola tuberifera put more resources into the reproduction of subterranean cleistogamous flowers and bulb.4. The sexual and asexual propagation of Viola tuberifera obviously responsed to heterogeneity resources. In sexual propagation, CH flowers and subterranean cleistogamous flowers were greatest responsed to heterogeneity resources. Meadow habitat had adequate light, but the competition is very fierce. Therefore, the main breeding mainly in CH flowers, the breeding of subterranean cleistogamous flowers was limited. Mound habitat had sufficient sunlight, rich in resources and loose soil, so the reproduction of CH flowers and subterranean cleistogamous flowers were dominant. The number of the seed of subterranean cleistogamous flowers was the highest in shrub because it had low light. Besides, in the vertical structure, it was part of the lower layer. The number of the aerial CL flowers had no significant differencesin the four kinds of habitat. Moreover, the bulb number of Viola tuberifera was mound> forest edge>shrub>meadow.5. The subterranean cleistogamous flowers of Viola tuberifera was located in stolons internodes, its seeds could be dispersed through the extension of stolons. The dispersal distance of seeds was gradually reduced with the rise of altitude. Visibly,along with environmental conditions worse, Viola tuberifera tended to keep the seeds near the mother plant, thus save offsprings near the favorable microenvironment of mother plant.6. Habitat had significant influence on the dispersal distance of the seeds of subterranean cleistogamous flowers. Mound habitat had loose soil and low community total coverage, the dispersal distance of the seeds of subterranean cleistogamous flowers was the farthest; but meadow habitat had various species, so community total coverage was high and there was a more intense interspecific competition. Additionally, human activities, the interference of grazing and trampling of animals made meadow soil texture hard, more compaction, so the dispersal distance of the seeds of subterranean cleistogamous flowers was the nearest in four different habitats.