Roots constitute a major segment of plant biomass, and variation in belowground traits in situ correlates with environmental gradients at large spatial scales. Local adaptation of populations maintains intraspecific genetic variation in various shoot traits, but the contribution of genetic factors to adaptation to soil heterogeneity remains poorly known. I established a common-garden experiment with three Norway spruce Picea abies populations sampled between 60° and 67° N in Finland, each represented by 13 or 15 maternal families, to determine whether belowground traits are as genetically differentiated among populations as those in the shoot along a collective latitudinal gradient of temperature and soil heterogeneity. Two growing season simulations enabled testing for among-population differences in phenotypic plasticity. I phenotyped 777 first-year seedlings from shoot to root to capture functional traits that may influence survival in the wild: autumn phenology, shoot growth, root system size, root architecture, root morphology and growth allocation. All traits exhibited within-population genetic diversity, but among-population differentiation ranged from strong in shoot traits to nonexistent in root system architecture and morphology that are scaled to root system size. However, latitudinal trends characterised root-to-shoot ratio and root tip-to-shoot ratio that account for among-population differences in aboveground growth. Overall trait variability was multidimensional with variable among- versus within-population trends: for example, phenology and shoot growth covaried across populations, but their association within individual populations was variable. Shoot growth correlated positively with root system size, but not with root architecture or morphology. Finally, the two higher-latitude populations exhibited greater phenotypic plasticity in shoot traits and growth allocation. The results demonstrate varying patterns of genetic variation in functional traits of Norway spruce in the boreal zone, suggesting simultaneous adaptation to multiple environmental factors. Functional traits that exhibit phenotypic plasticity, genetic diversity and little covariation will promote long-term survival of populations in fluctuating environments.

中文翻译：

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挪威云杉冷杉枝条和根功能性状沿纬度梯度的遗传多样性模式不同

根系构成植物生物量的主要部分，原位地下性状的变化与大空间尺度的环境梯度相关。种群的局部适应保持了各种枝条性状的种内遗传变异，但遗传因素对适应土壤异质性的贡献仍然知之甚少。我用三种挪威云杉冷杉建立了一个公共花园试验在芬兰北纬 60° 和 67° 之间采样的种群，每个种群由 13 或 15 个母系家庭代表，以确定地下特征在种群之间的遗传差异是否与沿温度和土壤异质性的集体纬度梯度的枝条中的特征一样。两个生长季节模拟能够测试种群间表型可塑性的差异。我对 777 株第一年幼苗从芽到根进行了表型分析，以捕捉可能影响野外生存的功能特征：秋季物候、芽生长、根系大小、根结构、根形态和生长分配。所有性状都表现出种群内遗传多样性，但种群间的分化范围从强烈的枝条性状到根系结构和形态不存在，这些差异与根系大小有关。然而，纬度趋势表征了根茎比和根尖茎比，这说明了地上生长的种群间差异。整体性状变异是多维的，种群间和种群内趋势是可变的：例如，物候和枝条生长在种群间共变，但它们在个体种群内的关联是可变的。枝条生长与根系大小呈正相关，但与根结构或形态无关。最后，两个高纬度种群在枝条性状和生长分配方面表现出更大的表型可塑性。结果表明，北方地区挪威云杉功能性状的遗传变异模式不同，表明同时适应多种环境因素。表现出表型可塑性、遗传多样性和很少协变的功能性状将促进种群在波动环境中的长期生存。