Kitamura Keiko, Nakanishi Atsushi, Lian Chunlan, Goto Susumu
Hokkaido Research Center, Forestry and Forest Products Research Institute, Forest Research and Management Organization, Sapporo, Japan.
Asian Natural Environmental Science Center, The University of Tokyo, Tokyo, Japan.
Front Genet. 2018 Oct 24;9:490. doi: 10.3389/fgene.2018.00490. eCollection 2018.
Conifers in northern forests, such as fir and spruce, preferably regenerate on coarse woody debris, including fallen logs, stumps, and snags. In northern Japan, the sub-boreal conifer species is completely dependent on coarse woody debris for seedling establishment. To understand the fine-scale spatial genetic structure (FSGS) of this species, a 5-ha plot was established in central Hokkaido, and 531 individual trees were categorized into four life-stages (seedling, sapling, juvenile, and mature) on the basis of age and size. The FSGS of the established seedlings and later growth stages was investigated using 11 nuclear simple sequence repeat loci. A STRUCTURE analysis of seedlings and saplings established on fallen logs revealed that genetically related individuals were spatially localized between adjacent logs. We also found a significant FSGS in early life-stages based on a decline in the kinship coefficient calculated between individuals over shorter to longer spatial distances. Furthermore, the estimation of dispersal kernels indicated the frequent occurrence of short-distance seed dispersal. These results indicated that genetically related seedlings and saplings regenerated on the same or nearby fallen logs. In contrast to the results for the early stages, mature-stage trees showed no significant FSGS. We ran a simulation to examine the hypothesis that the FSGS could be eliminated by demographic thinning during life history processes. We calculated values for simulated offspring generated under three sets of conditions; i.e., by removing (i) inbred individuals, (ii) randomly chosen individuals, and (iii) all individuals on the specific fallen logs. However, the results for the FSGS were significant for all simulated data sets. This indicated that inbreeding depression, stochastic loss, or eradication of establishment sites by local disturbances alone could not explain the lack of FSGS among mature-stage trees. Therefore, it is possible that the colonization history of mature trees present on the study site might differ from that of the current offspring.
北方森林中的针叶树，如冷杉和云杉，更倾向于在粗木质残体上更新，包括倒下的原木、树桩和枯立木。在日本北部，亚寒带针叶树种完全依赖粗木质残体来建立幼苗。为了了解该物种的精细尺度空间遗传结构（FSGS），在北海道中部建立了一个5公顷的样地，并根据年龄和大小将531棵个体树分为四个生命阶段（幼苗、幼树、小树和成熟树）。使用11个核简单序列重复位点研究了已建立的幼苗和后期生长阶段的FSGS。对在倒下的原木上建立的幼苗和幼树进行的STRUCTURE分析表明，遗传相关个体在相邻原木之间在空间上是局部化的。我们还发现，基于个体之间在较短到较长空间距离上计算的亲缘系数下降，早期生命阶段存在显著的FSGS。此外，扩散核的估计表明短距离种子扩散频繁发生。这些结果表明，遗传相关的幼苗和幼树在同一或附近倒下的原木上更新。与早期阶段的结果相反，成熟阶段的树木没有显示出显著的FSGS。我们进行了一项模拟，以检验FSGS可能在生命历史过程中通过种群数量减少而消除的假设。我们计算了在三组条件下产生的模拟后代的值；即，通过去除（i）近交个体，（ii）随机选择的个体，以及（iii）特定倒下原木上的所有个体。然而，所有模拟数据集的FSGS结果都是显著的。这表明近交衰退、随机损失或仅由局部干扰导致的定居点根除不能解释成熟阶段树木中缺乏FSGS的现象。因此，研究地点现存成熟树木的定殖历史可能与当前后代的定殖历史不同。
