The Reproductive Ecology Of Four Ephemeral Species Of Trigonella

With the aid of the fluorescence microscope, scanning electron microscope (SEM), biostatistics methods, and field investigation, the characteristics of phenology, breeding system, the fruit and seed set patterns, the reproductive allocation dynamics and the fruit and seed dispersal mechanism of four ephemeral species of Trigonella (T. cancellata, T. arcuata, T. monantha and T. orthoceras) grown in Junggar desert were studied in this thesis. Species-specific life-history strategies and reproductive countermeasurements were analyzed. The underlying adaptive mechanism of the 4 species to arid environment and its ecological significance were discussed. The main results show as follows: 1) The phenological characteristics : the 4 species showed different germination strategies. Seeds of the 4 species could germinated in spring, summer and autumn, although the germination frequency was higher in spring and autumn than in summer. The germination time was very closely related to the environment factors, such as the temperature, the precipitation and so on. There was no significant inter-specific difference in germination time. The growth rhythm was quick and the life cycle is short in all the four species. The fruits have maturated before the arrival of arid summer season. On all accounts, the four species are monocarpic, and their life-history strategy belongs to the type of escaping arid. 2) The breeding system characteristics : P/O of the 4 species were ranged from 30 to 150. The correlations between the growth of different modules of a flower were significant. Compared with pre-pollen dispersal period, the spatial position of pistil and androecium have changed after pollen dispersal. The pollen vitality was reduced to less than 20% after 4h of anther's rupture , and the petal splayed after 16～24 h of anther's rupture. In the self-mating experiment, the self pollen germinated on the stigmas and the pollen tube elongated. There was no significant difference in the percentage of seed set between the self and the control experiment. The insect pollinators have not been observed during the florescence period. 3) The fruit set and seed set patterns: the patterns of fruit set were closed related to the position of inflorescence on tress, the upper-and lower-fruits were different in biomass and number of the seed set ; the patterns of seed set were related to the position of ovule in ovary. These patterns could be explained by the theory of resource limitition . 4) The biomass allocation :As a response to the change of surrounding environment, the four species adjust the proportion of resource allocation between the vegetative growth and the reproductive growth, the reproductive yield of the spring-and autumn-germinated plants were maximized by an instantaneous switch from vegetative to reproductive growth after a short period of vegetative growth. The four species have high proportion of reproductive allocation with 62.3%, 51.9%, 54.3% and 58.3%, respectively, and the absolute measures of reproductive output were size-dependent. The difference of reproductive output between the autumn-and the spring-germinated plants were significant. 5) The dispersal mechanism : the dispersal distance of fruits and seeds was correlated with the length of stalks. Besides spontaneous shedding, seeds were also disseminated by ants and vegetarians.