濒危植物四合木结实特性与植株年龄和生境关系的研究

A STUDY ON THE RELATIONSHIP BETWEEN FRUITING CHARACTERISTICS AND REPRODUCTIVE AGE,HABITAT OF ENDANGERED SPECIES TETRAENA MONGOLICA

研究了濒危植物四合木种群初次结实年龄 ,果实空间分布、果实数量、果实重量、结籽率、花果转移率随年龄和生境的变化规律。结果表明 :四合木种群初次结实年龄为 4a。果实的空间分布为树冠上部 >中部 >下部 ,上、中部显著高于下部。平均单株果实的数量分布随年龄变化曲线呈山峰型。在 4～ 1 8a范围内 ,随着年龄增大 ,结实量增加 ,到 1 8a以后 ,随着年龄增加 ,结实量逐渐减少 ,1 3～ 2 7a为结实高峰期。果实重量随年龄变化趋势与果实数量随年龄变化趋势基本一致。在自然状态下 ,四合木结籽率为 1 2 6%～ 2 80 % ,花果转移率为 5 4 3 9%～ 71 43 % ,结籽率、花果转移率与年龄的关系呈双峰型。结籽率低的主要原因为 :( 1 )传粉过程受到障碍 ,即传粉媒介 (昆虫 )的访花频率极低 ,使得柱头上的花粉量受到限制。这是结籽率低的内因。( 2 )土壤水分供应不足 ,从而使胚珠不能正常发育。这是导致结籽率低的外因。

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.