垂序商陆(Phytolacca americana)的入侵给山东省沿海防护林的生物多样性及乔木更新造成了严重的危害, 为揭示其繁殖特性和扩散机制, 在灵山湾国家森林公园刺槐(Robinia pseudoacacia)林下由林缘至林内60 m设置5个梯度, 采用机械布点法对垂序商陆的结实量、种子雨分布和扩散格局进行了调查。结果表明: 1)垂序商陆的结实量与种子雨量由林缘至林内逐渐减小, 分别为2 273-1 846和1 382-621粒·m^-2, 不同空间种子雨密度占结实密度的60.80%-33.64%, 平均为49.52%, 人为搂割及动物取食是种子雨量损失的主要原因; 2)种子雨始于9月中旬, 林缘种子雨的发生早于林内, 种子雨的平均强度由林缘至林内逐渐减小, 在10月下旬和12月中旬各有一次种子雨高峰, 最大强度分别为32-4和59-5粒·m^-2·d^-1; 3)种子雨由林缘至林内散布范围逐渐减小, 同时随距母株距离的增加而减小, 其中最大散布距离与加权平均距离分别为210-180 cm和94.32-63.03 cm, 整体加权平均距离为81.00 cm。表明垂序商陆种子雨具有明显的时空异质性, 对预测其扩散潜力及群落结构组成趋势有重要的意义。

Aims Phytolacca americana is a serious invasive plant species, which has harmed biodiversity and arboreal regeneration in coastal protective forests in Shandong Province. Our objective was to reveal its mechanism of reproduction and dispersal in order to provide guidance for controlling its invasion.

Methods To study the spatial and temporal pattern of seed rain of P. americana, we conducted field surveys under Robinia pseudoacacia forest in Lingshan Bay National Forest Park from September to December 2008. We established five transects at 15 m intervals from forest edge to forest interior and within each transect set up 30 samples (1 m × 1 m) to survey seed densities. We also chose eight mother plants of P. americana at 10 m intervals in each transect and placed seed traps (30 cm × 30 cm × 10 cm) at 11 sample points at every 30 cm surrounding them. We collected fallen seeds one or two days. One-way ANOVA was used to test the diversity.

Important findings The quantities and densities of seed rain were 1 846-2 273 seeds and 621-1 382 seeds per square meter, respectively, and values decreased from forest edge to interior. In five transects, the average seed rain densities were 33.64%-60.80% of reproduction, and the total average seed rain density accounted for 49.52% of seed reproduction densities; the rest was removed by firewood collecting and seed predation by animals. Seed rain began in mid September and ended in late December, and it occurred on forest edges before forest interiors. There were two seed-rain peaks in late October and mid December, and maximum intensities were 32 and 59 seeds per square meter per day, respectively. The dispersal distance of seed rain decreased from forest edge to forest interior. The same pattern existed with increasing distance from mother plant. The maximal dispersal and weighted mean distances were 210-180 cm and 94.32-63.03 cm, respectively; the average weighted mean distance was 81.00 cm. Phytolacca americana seed rain had obvious spatio-temporal heterogeneity. Findings were important to predict the invasive potential of P. americana and the trend in community structure.