生境片段化对千岛湖马尾松林内土壤种子库的影响

土壤种子库是森林群落更新的主要来源之一,对森林的演替和恢复等具有重要意义。生境片段化现象正日益严重地影响着森林群落,并可影响森林土壤种子库。研究了千岛湖地区的大陆及岛屿次生马尾松林内土壤种子库的组成及其影响因素(e.g.,岛屿面积,形状指数,隔离度和距岛屿边缘距离等)。根据大陆和岛屿的面积及边缘梯度,采用大数量小样方法,分别在土壤种子库最大化(初冬,2015年12月)和最小化(晚春,2016年4月)时期对马尾松林内土壤进行了机械取样。对土壤样品进行萌发实验,检测了两个时期的土壤种子库上层(0—2 cm)和下层(2—5 cm)种子组成,并通过广义线性混合效应模型等手段分析其影响因素。结果显示:(1)所有316个土壤样本中,萌发出幼苗1422株,隶属于29科、40属、41种。其中,木本植物幼苗占13种1024株,草本占28种398株。(2)Jaccard指数和相关性分析均显示初冬、晚春时期的土壤种子库组成具有很高的相似性;土壤种子库上、下层组成的相似性也很高。(3)广义线性混合效应模型分析显示,在大陆和岛屿上,土壤种子库下层种子含量低于上层;而大陆样地土壤种子库中的木本植物种子数较岛屿样地高。岛屿上,土壤种子库中的种子数随土层的加深而降低;随边缘梯度升高也下降,尤其是草本植物的种子。对于岛屿上的木本植物,不耐阴种的种子数量远大于耐阴种,尤其是土壤下层。表明千岛湖地区马尾松林内土壤种子库组成受到生境片段化的影响,进而可能作用于该类型森林群落的演替。

Effects of habitat fragmentation on the soil seed banks of Masson pine (Pinus massoniana) forests in the Thousand Island Lake region, eastern China

As a major source of forest regeneration, soil seed bank critically influences forest succession and restoration. Habitat fragmentation increasingly affects forest systems, which could in turn alter forest soil seed bank. Here, to explore how habitat fragmentation (e.g. island size, shape, isolation and distance from island edge) influences forest soil seed bank, we studied soil seed bank composition of the secondary Masson pine forests on mainland and 29 study islands in the Thousand Island Lake region, eastern China. By adopting the "large number of small samples" method, we systematically sampled Masson pine forest soils in December (early winter) 2015 and April (late spring) 2016. Then we conducted germination experiment to estimate soil seed bank compositions of the upper (0-2 cm) and lower (2-5 cm) soil layers. We found that (1) 1422 seedlings belonging to 41 species, 40 genera and 29 families were germinated from 316 soil samples, among which woody plant seedlings comprised 1024 individuals, 13 species and herbaceous plant seedlings comprised 398 individuals, 28 species. (2) Results of Jaccard index and correlation analyses both indicated the soil seed bank composition was very similar between early winter and late spring, and between upper and lower soil layers. (3) Generalized linear mixed-effects modeling results implied the lower soil layer harbored fewer seeds than the upper soil layer for mainland and island forests combined. Compared with mainland, island forest soil harbored more seeds of herbaceous plants than woody plants. In island forests, the lower soil layer harbored less seeds than the upper soil layer; seed number in soil decreased as distance from edge increased, especially for herbaceous plants; among woody plant seeds, seed number of shade-intolerant plants was considerably larger than that of shade-tolerant plants, especially for the lower soil layer. The results suggest the soil seed bank composition of Masson pine forests in the Thousand Island Lake region was altered by habitat fragmentation, which might influence the succession of Masson pine forest communities.