Abstract:

Tetraena mongolica belonging to Zygophyllaceae is the ancient relic plant of Tethys seatropical floristic region. It only distributes from Bayan Gele, west of Inner Mongolia Autonomous Region to Shizui Mountain, east of Ninxia Hui Autonomous Region. T. mongolica, which plays the important role in the windbreak sand-fixation and soil and water conservation, is on the verge of endanger in recent years, so it is listed as the second-class national key plant for protection. In order to probe the mechanism of endanger of T. mongolica, this paper dealt with the initial fruiting age, the distribution, quantity, and weight of fruits, transformation rate from flowering to fruiting, and the relationship between fruiting rate and age of T. mongolica, and analyzed the cause of low fruiting rate. Total 70 plots with the size of 10m×10m each were set up in two sample strips with the size of 10m×3 800m each, and the community composition, base diameter, crown width, and the number of the individual trees of T. mongolica, soil moisture and pH of plots were investigated. The age of the trees was identified by the ring method. 5 individual trees of each age class at intervals of 3a were sampled, and the transformation rate from flower to seed and seed bearing rate were surveyed. The method of nylon net with hole size 1mm×1mm was used in 8 sample trees to calculate seed bearing rate and to analyze the cause of low rate of seed bearing. The results showed: 4 years old T. mongolica was in the initial fruiting age, the spatial sequence of fruiting distribution in the individual tree was upper, middle, and lower part of the crown,and seed production with the change of individual age was in the one-peak type curve. With the age increase of individual, the number of fruit bearing increased from 4 to 18 years old, and declined after 18 years old. 15～27 years old was peak period for fruit bearing. The change of fruit weight with age showed the similar curve to the former, and the rate of seed bearing varied from 1.26% to 2.80%. The change of seed bearing rate showed 2-peak type curve over age.

Key words: Endangered plant, Tetraena mongolica, Fruiting characteristics, Age, Habitat, Seed bearing percentage