Data from: Timing of mutualist arrival has a greater effect on Pinus muricata seedling growth than interspecific competition

Interactions with symbiotic microbes, such as mycorrhizal fungi, have the potential to greatly influence plant growth, but it is unclear whether field variation in symbiont availability is common and, if so, sufficient to influence interspecific plant competition.
In a greenhouse experiment using natural field soils, I varied the timing of ectomycorrhizal inoculation and the presence of an arbuscular mycorrhizal plant competitor, and measured their effects on pine seedling growth.
I found that ectomycorrhizal colonization was absent in some field soils, and that in soils without mycorrhizal inoculum, delayed arrival of ectomycorrhizal spores progressively reduced pine seedling growth and favoured growth of the competitor. Competition had significant negative effects on pine seedling growth, but the competition effect was much smaller than the effect of delayed mutualist arrival.
Synthesis. The importance of mycorrhizal spore arrival time on pine growth suggests that plants may experience mutualist limitation more frequently than previously expected, and the relative magnitude of seedling responses to mycorrhizal fungi and competing plants show that in some systems mutualism is likely of equal or greater importance compared with interspecific competition in affecting plant community assembly.

与菌根真菌（mycorrhizal fungi）等共生微生物的互作，具备显著调控植物生长的潜力，但目前尚不明确：共生体可获取性的田间变异是否普遍存在，若普遍存在，其是否足以影响植物种间竞争。
本研究依托天然田间土壤开展温室试验，设置外生菌根（ectomycorrhizal）接种时机与丛枝菌根（arbuscular mycorrhizal）植物竞争者的有无两个变量，探究二者对松属幼苗生长的影响。
研究结果表明，部分田间土壤中未发生外生菌根定殖；在不含菌根接种体的土壤中，外生菌根孢子的延迟定殖会逐步抑制松属幼苗生长，并促进竞争者的生长。种间竞争对松属幼苗生长具有显著负向影响，但其作用强度远低于共生伙伴延迟定殖的效应。
研究综合：菌根孢子定殖时机对松属幼苗生长的关键作用表明，植物面临共生体限制的频率可能高于此前预期；幼苗对菌根真菌与竞争者的响应强度对比显示，在部分生态系统中，共生互作在调控植物群落构建过程中的重要性，可与种间竞争相当甚至更甚。