Table_5_Genetic Diversity, Structure and Effective Population Size of Old-Growth vs. Second-Growth Populations of Keystone and Long-Lived Conifer, Eastern White Pine (Pinus strobus): Conservation Value and Climate Adaptation Potential.pdf

Whether old-growth (OG) forests have higher genetic diversity and effective population size, consequently higher conservation value and climate adaptive potential than second-growth (SG) forests, remain an unresolved issue. We have tested the hypothesis that old-growth forest tree populations have higher genetic diversity, effective population size (NE), climate adaptive potential and conservation value and lower genetic differentiation than second-growth forest tree populations, employing a keystone and long-lived conifer, eastern white pine (EWP; Pinus strobus). Genetic diversity and population structure of old-growth and second-growth populations of eastern white pine (EWP) were examined using microsatellites of the nuclear and chloroplast genomes and single nucleotide polymorphisms (SNPs) in candidate nuclear genes putatively involved in adaptive responses to climate and underlying multilocus genetic architecture of local adaptation to climate in EWP. Old-growth and second-growth EWP populations had statistically similar genetic diversity, inbreeding coefficient and inter-population genetic differentiation based on nuclear microsatellites (nSSRs) and SNPs. However, old-growth populations had significantly higher chloroplast microsatellites (cpSSRs) haploid diversity than second-growth populations. Old-growth EWP populations had significantly higher coalescence-based historical long-term NE than second-growth EWP populations, but the linkage disequilibrium (LD)-based contemporary NE estimates were statistically similar between the old-growth and second-growth EWP populations. Analyses of population genetic structure and inter-population genetic relationships revealed some genetic constitution differences between the old-growth and second-growth EWP populations. Overall, our results suggest that old-growth and second-growth EWP populations have similar genetic resource conservation value. Because old-growth and second-growth EWP populations have similar levels of genetic diversity in genes putatively involved in adaptive responses to climate, old-growth, and second-growth populations may have similar adaptive potential under climate change. Our results could potentially be generalized across most of the boreal and temperate conifer forest trees. Our study contributes to address a long-standing issue, advances research field and knowledge about conservation and ecological and climate adaptation of forest trees.

原始老龄林（old-growth forests, OG）是否较次生林（second-growth forests, SG）拥有更高的遗传多样性与有效种群大小，进而具备更高的保护价值与气候适应潜力，这一科学问题迄今仍未得到明确解答。本研究以关键长寿针叶树种北美东部白松（eastern white pine, EWP; *Pinus strobus*）为研究材料，对下述假说展开检验：原始林林木种群相较于次生林林木种群，具有更高的遗传多样性、有效种群大小（N_E）、气候适应潜力与保护价值，且种群间遗传分化程度更低。研究采用核基因组与叶绿体基因组微卫星标记，以及参与气候适应响应的候选核基因单核苷酸多态性（SNPs），分析了北美东部白松原始林与次生林种群的遗传多样性及种群结构，并解析了该物种气候局部适应的多位点遗传架构。基于核微卫星（nSSRs）与SNPs的数据，原始林与次生林EWP种群的遗传多样性、近交系数及种群间遗传分化均无统计学显著性差异。但原始林种群的叶绿体微卫星（cpSSRs）单倍型多样性显著高于次生林种群。基于溯祖理论估算的历史长期有效种群大小，原始林EWP种群显著高于次生林种群；而基于连锁不平衡（LD）估算的当代有效种群大小，两类种群间则无显著差异。种群遗传结构与种群间遗传关系分析结果显示，原始林与次生林EWP种群存在一定的遗传组成差异。总体而言，本研究结果表明，原始林与次生林EWP种群的遗传资源保护价值相当。鉴于两类种群在与气候适应响应相关的候选基因中具有相似水平的遗传多样性，二者在气候变化背景下或具备相似的气候适应潜力。本研究结果或可推广至大多数北方与温带针叶林树种。本研究有助于解决这一长期存在的科学争议，推动林木保护、生态学及气候适应相关研究领域的认知与发展。