灵山湾国家森林公园垂序商陆土壤种子库时空动态及其对防除措施的响应

土壤种子库是植物潜在的种群,对生态系统稳定和未来植被的结构、功能有着举足轻重的影响。垂序商陆(Phytolacca americana)的入侵已对山东省胶南市灵山湾国家森林公园的森林生态系统构成严重危害。为调查该物种在公园内的潜在扩散能力,于2009—2014年调查了刺槐(Robinia pseudoacacia)林、黑松(Pinus thunbergii)林、刺槐黑松混交林和紫穗槐(Amorpha fruticosa)林(灌丛)4种林分类型,以及2009年采用物理和化学控制入侵危害严重的刺槐林内的土壤种子库。结果表明:垂序商陆种子在4种林分中均有发现,在刺槐、黑松林内表现为由林缘至林内逐步降低的趋势。垂序商陆种子只存在于枯落物层和5 cm以上的土壤中,随土层深度的增加而减少,枯落物层土壤种子库由林缘到林内呈递减趋势。与2009年相比,2014年黑松林和灌丛中平均种子库密度分别降低46%和44%,刺槐林和混交林分别增加299%和355%。垂序商陆种子发芽率在10%以下,随土层深度的增加而依次降低。采用物理、化学控制措施的刺槐林内垂序商陆的更新量、结实量、种子库含量均明显高于紫穗槐林的。调查结果表明垂序商陆土壤种子库具有明显的空间异质性,并且保持了较强的繁殖潜力,营造紫穗槐灌丛可以有效控制垂序商陆的扩散,可为经营沿海防护林提供理论指导。

Spatiotemporal dynamics of soil seed bank of Phytolacca americana and its response to control measures in coastal protective forests in Lingshan Bay National Forest

Soil seed banks are potential plant communities. Their temporal and spatial distribution patterns play an important role in future plant community dynamics and structure. Characteristics of the seed bank for Phytolacca americana affect the construction and function of future ecosystems in the invaded area. The ecological balance in the coastal shelter forest ecosystems in the Lingshan Bay National Forest Park has been severely affected by Phytolacca americana. Between 2009 and 2014, we studied seed density and distribution pattern of Phyolacca americana in Pinus thunbergii forest, Robinia pseudoacacia forest, mixed Pinus thunbergii and R. pseudoacacia forest, and Amorpha fruticosa forest. We established five transects at 15 m intervals from the forest edge to the interior, set up 40 samples in each transect, and collected soil seed banks from the litter layer, 0-2 cm soil layer, and 2-5 cm soil layer. We conducted a control trial in the R. pseudoacacia forest, which was extensively invaded by Phytolacca americana in 2009. We used physical (mowing and root cutting) and chemical (spraying herbicides) methods to control the growth of Phytolacca americana and chose A. fruticosa as the control. We investigated the seed bank in the control area, counted the number of seeds, and performed a germination test in the laboratory. The seeds of Phytolacca americana were found in all four types of forests, and the content of the seed bank decreased from the forest edge to the interior of the forest in the R. pseudoacacia and Pinus thunbergii forests. All the seeds were found within the top 5 cm of the soil layer, within which the lowest number of seeds was found in the 2-5 cm layer. We found (1174±713) seeds/m² in one month in the seed bank from the R. pseudoacacia forest in 2009; the number of seeds increased to (3207±1072) seeds/m² in October, in 2012 and (4691±1597) seeds/m² in January, in 2014. In the mixed forest, we found (388±713), (1074±713), and (1767±713) seeds/m² in the seed bank in 2009, 2012, and 2014, respectively. Between 2009 and 2014, less than 1000 seeds/m² were found in the seed bank from the Pinus thunbergii and A. fruticosa forests. We compared the results of the two seed bank surveys conducted during 2009-2014: in the Pinus thunbergii and A. fruticosa forests, the number of seeds decreased by 46% and 44%, respectively, whereas in the R. pseudoacacia and mixed forests, an increase by 29.9% and 35.5%, respectively, was noted. The seed germination rate was less than 10% and decreased from the litter layer to the 2-5cm layer. Seedling regeneration, seed yield, and seed bank in the A. fruticosa forest were significantly lower than those in the forests where physical and chemical control methods were used. Physical and chemical control methods are useful in controlling Phytolacca americana; however, their effects are temporary and the use of biological control seems more practical. Our study showed that the seed bank of Phytolacca americana had an evident spatio-temporal heterogeneity, maintained a high reproductive potential, and can be used to control the invasion of Phytolacca americana by planting A. fruticosa. Our findings can help in the sustainable management of coastal shelter forests.