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<p>Tree growth strategy is strongly influenced by competitive pressure, which shapes the overall architecture and morphology of resource-capturing organs. However, the morphological acclimation of trees, particularly that of the belowground parts, to varying intensities of competition and different climatic conditions is still poorly understood. We evaluated the architectural parameters, leaf and fine root morphology, biomass partitioning and chemical composition of the leaves and absorbing roots of 7-year-old silver birch (<i>Betula pendula</i> Roth) individuals experiencing different levels of competitive pressure in a monocultural stand under two treatments: increased relative humidity (RH) and increased soil moisture, in a free air humidity manipulation (FAHM) experiment. Across all treatments, stronger asymmetric competition influenced aboveground morphology—birches prioritised height growth, accompanied by an increased stem length-to-mass ratio and higher specific leaf area (SLA) of sun leaves. In contrast, intensified symmetric competition influenced both leaf and root traits, leading to a higher proportion of absorptive roots within the fine root biomass, a smaller absorptive root diameter, an increase in shade leaf SLA, and a decrease in leaf mass fraction. These adaptations enabled improved resource capture without necessitating additional biomass investment under conditions of resource scarcity. In more humid environments, where elevated RH reduces evapotranspiration and irrigation prevents water shortages, fine roots showed lower carbon isotopic composition, indicating enhanced canopy stomatal conductance. At the same time, crown length relative to tree height, sun leaf area, and specific leaf area increased under humidification and irrigation. Such adjustments may, however, increase the susceptibility of birches to summer drought events.</p>

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Above- and belowground acclimation of morphological traits of silver Birch to competition conditions and elevated moisture regimes of air and soil

  • 期刊论文

  • 发表日期：

    2026年3月5日

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  • Katrin Rosenvald,
  • Marco M. Lehmann,
  • Ivika Ostonen,
  • Gristin Rohula-Okunev,
  • Priit Kupper,
  • Arvo Tullus

摘要

Tree growth strategy is strongly influenced by competitive pressure, which shapes the overall architecture and morphology of resource-capturing organs. However, the morphological acclimation of trees, particularly that of the belowground parts, to varying intensities of competition and different climatic conditions is still poorly understood. We evaluated the architectural parameters, leaf and fine root morphology, biomass partitioning and chemical composition of the leaves and absorbing roots of 7-year-old silver birch (Betula pendula Roth) individuals experiencing different levels of competitive pressure in a monocultural stand under two treatments: increased relative humidity (RH) and increased soil moisture, in a free air humidity manipulation (FAHM) experiment. Across all treatments, stronger asymmetric competition influenced aboveground morphology—birches prioritised height growth, accompanied by an increased stem length-to-mass ratio and higher specific leaf area (SLA) of sun leaves. In contrast, intensified symmetric competition influenced both leaf and root traits, leading to a higher proportion of absorptive roots within the fine root biomass, a smaller absorptive root diameter, an increase in shade leaf SLA, and a decrease in leaf mass fraction. These adaptations enabled improved resource capture without necessitating additional biomass investment under conditions of resource scarcity. In more humid environments, where elevated RH reduces evapotranspiration and irrigation prevents water shortages, fine roots showed lower carbon isotopic composition, indicating enhanced canopy stomatal conductance. At the same time, crown length relative to tree height, sun leaf area, and specific leaf area increased under humidification and irrigation. Such adjustments may, however, increase the susceptibility of birches to summer drought events.