Abstract
Globally, alpine treelines are characterized as temperature-limited environments with strong controls on tree growth. However, at local scales spatially heterogeneous environments generally have more variable impacts on individual patterns of tree growth. In addition to the landscape spatial heterogeneity there is local variability in individual tree genetic diversity (level of individual heterozygosity). It has been hypothesized that higher individual heterozygosity will result in more consistent patterns of growth. In this article, we combine genomics and dendrochronology to explore the relationship between individual genetic diversity and tree growth at a mountain hemlock (Tsuga mertensiana Bong. Carr) alpine treeline on the Kenai Peninsula, Alaska, USA. We correlated average observed individual heterozygosity with average tree-ring width and variance in tree-ring width within individuals to test the hypothesis that trees with higher individual heterozygosity will also have more consistent growth patterns, suggesting that they may be more resilient to climate and environmental fluctuations at the alpine treeline. Our results showed that there was no significant relationship between tree growth and individual heterozygosity. However, there was a significant positive relationship between average tree-ring width and variance in tree-ring width implying that overall, fast growing trees in stressful environments, such as the alpine treeline, grow unstably regardless of the level of individual heterozygosity.
Highlights
Patterns of forest tree growth at landscape and regional scales are often affected by changes in broad scale site quality and climate [1]
We identified 4665 single nucleotide polymorphism (SNP) distributed across the mountain hemlock genome
Two individuals had greater than 15% missing genotype information and were removed from genomic analysis
Summary
Patterns of forest tree growth at landscape and regional scales are often affected by changes in broad scale site quality and climate [1]. Many characteristic growth patterns in trees, such as leaf size [4], shape [5], height [6] and radial growth [7] are linked to environmental factors like temperature [8], moisture availability [4,5,9], competitive interactions [10,11], and stress [12]. Alpine treeline represents a harsh environment with strong influence on spatial patterns of radial growth [7,16,17]. If plants have higher genetic diversity (individual heterozygosity), do they have more consistent and stable growth patterns (homeostasis) relative to environmental variation [18,19] like that found at the alpine treeline?
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