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 and leaf N uptake by 38%, 52% and 76%, without differences between the responses of fast-growing and slow-growing genotypes, whereas root mass decreased with increasing grass cover. Shoot and leaf growth of fast-growing genotypes decreased and EM fungal production of slow-growing genotypes increased with increasing grass cover. Our results suggest that fast growth is genotypically associated with higher allocation to EM fungi, better soil N capture and greater leaf production, and that the tradeoff of fast growth is sensitivity to competition, but not to insect herbivory. EM fungi may have a dual role: to support growth of fast-growing genotypes under low grass competition and to maintain growth of slow-growing genotypes under intensifying competition.

建议快速生长和缓慢生长的植物物种显示出综合经济光谱，并且预计快速生长的权衡将成为草食性和资源竞争的易感性。我们测试了这些预测是否也适用于白桦（ Betula pendula ）种群中快速增长和缓慢增长的基因型。我们使用杀虫剂将具有缓慢、中等或快速高度生长的 17 种基因型的克隆树苗暴露于减少的昆虫食草，并使用自然变化的田间草覆盖物来增加资源竞争。我们使用麦角甾醇分析测量了枝条和根的生长、外生菌根 (EM) 真菌的产生，并使用^{15 N 标记的 NH} ₄ ⁺脉冲测量了土壤 N 向叶子的转移. 我们发现，与生长缓慢的基因型相比，快速生长的基因型平均生长速度快 78%，产生的叶质量和麦角甾醇分别增加 56% 和 16%，并且叶片氮吸收量高 78%。杀虫剂减少了 83% 的叶片损伤，增加了 38%、52% 和 76% 的枝条生长、叶片生长和叶片 N 吸收，快速生长和缓慢生长基因型的反应之间没有差异，而根质量随着增加草覆盖。随着草盖度的增加，快速生长基因型的枝条和叶片生长减少，而慢速基因型的 EM 真菌产量增加。我们的研究结果表明，快速生长与 EM 真菌的更高分配、更好的土壤 N 捕获和更大的叶片产量在基因型上相关，并且快速生长的权衡是对竞争的敏感性，而不是对昆虫食草的敏感性。