Genotypic traits and tradeoffs of fast growth in silver birch, a pioneer tree

Fast-growing and slow-growing plant species are suggested to show integrated economics spectrums and the tradeoffs of fast growth are predicted to emerge as susceptibility to herbivory and resource competition. We tested if these predictions also hold for fast-growing and slow-growing genotypes within a silver birch, Betula pendula population. We exposed cloned saplings of 17 genotypes with slow, medium or fast height growth to reduced insect herbivory, using an insecticide, and to increasing resource competition, using naturally varying field plot grass cover. We measured shoot and root growth, ectomycorrhizal (EM) fungal production using ergosterol analysis and soil N transfer to leaves using 15N-labelled pulse of NH4+. We found that fast-growing genotypes grew on average 78% faster, produced 56% and 16% more leaf mass and ergosterol, and showed 78% higher leaf N uptake than slow-growing genotypes. The insecticide decreased leaf damage by 83% and increased shoot growth, leaf growth an...学界普遍认为，速生与慢生植物类群呈现出整合的植物经济学谱（plant economics spectrum）；据预测，快速生长所伴随的生长权衡会体现为对植食作用的易感性与资源竞争能力的差异。本研究以垂枝桦（Betula pendula）种群内的基因型为对象，验证上述预测是否同样适用于种内的速生与慢生变异类型。我们借助杀虫剂降低昆虫植食危害，并利用野外样地中自然变化的草本覆盖度来调控资源竞争强度，对17种具有慢、中、快不同株高生长速率的基因型的克隆幼苗开展了处理。我们测定了地上与地下部分的生长情况，通过麦角固醇（ergosterol）分析法量化外生菌根（ectomycorrhizal, EM）真菌生物量，并采用15N标记的NH4+脉冲标记技术，测定了土壤氮素向叶片的转移量。结果显示，速生基因型的平均生长速度较慢生基因型高78%，叶片生物量与麦角固醇含量分别高出56%与16%，叶片氮素吸收量较慢生基因型高78%。杀虫剂使叶片受植食损伤程度降低83%，并促进了地上部分与叶片生长，……