荒漠孑遗植物裸果木种子时空扩散特性

裸果木(Gymnocarpos przewalskii)是亚洲中部荒漠区少有的第三纪孑遗物种,由于气候变化及人为干扰,其自然种群分布范围不断缩小。种子扩散作为植物生活史过程中的重要阶段,不仅对物种生存及其多样性至关重要,还影响物种分布范围和局部丰度。2015年和2016年分别在新疆哈密地区,采用布设种子收集器的方法,对其自然种群种子扩散的时空动态进行了定点连续观测。结果表明:该物种于当年6月上旬开始扩散,2015年略早于2016年。每年种子扩散持续时间约两个月,扩散趋势为单峰曲线,且呈集中大量扩散的模式,扩散高峰期与当年初次月降水高峰期吻合;在顺风的正南和东南方向上,种子扩散密度大且距离远;种子扩散主要集中在母株冠幅下,随着距母株距离的增加,种子扩散密度减少,二者间存在极显著的负相关性(P0.01),由于裸果木枝条繁多,对风力强度起到了一定的阻碍作用,可能是造成种子集中扩散在母株下的原因。裸果木种子扩散受外界环境(降水、风向)和自身因素等方面的影响,当种子在大量降水前完成扩散,将有利于种子在适宜的微生境萌发,是对多风、干旱的恶劣生境的一种长期适应。

Temporal and spatial characteristics of seed dispersal of the relict Gymnocarpos przewalskii in deserts

Gymnocarpos przewalskii is a rare Tertiary relict species found in the desert regions of Central Asia; the natural population distribution of G. przewalskii is declining owing to climate change and human interference. As an important life history stage of plants, seed dispersal is not only critical for the survival and diversity of species, but also affects the distribution and local abundance of species. In 2015 and 2016, seed traps were installed around G. przewalskii mother plants in different directions in Hami. The spatial and temporal dynamics of seed dispersal of this natural population were continuously observed. The results showed that seeds began to disperse in early June and seed dispersal in 2015 was slightly earlier than in 2016. Seed dispersal lasted about 2 months; the dispersal trend was a single peak curve and presents a pattern of mass dispersal. The peak of seed dispersal coincided with the peak of the first monthly precipitation of the year. Dispersal occurred at the highest density and for the longest distance south and southeast of downwind. The seeds were mainly concentrated directly underneath the canopy of the mother plant. As the distance from the mother plant increased, seed density decreased, and there was a very significant negative correlation between dispersal distance and dispersal density. The main reason for the high dispersal density of seeds of G. przewalskii under the mother plant is that its numerous branches weakened the wind strength through the plants. Seed dispersal of G. przewalskii was affected by precipitation, wind, and plant characteristics. Seed dispersal before heavy precipitation may be beneficial for seed germination in suitable microhabitats, which is a long-term adaptation of G. przewalskii to the harsh wind and drought conditions.