Data from: Order of arrival structures arbuscular mycorrhizal colonization of plants

Priority effects – the impact of a species' arrival on subsequent community development – have been shown to influence species composition in many organisms. Whether priority effects among arbuscular mycorrhizal fungi (AMF) structure fungal root communities is not well understood. Here, we investigated whether priority effects influence the success of two closely related AMF species (Rhizophagus irregularis and Glomus aggregatum), hypothesizing that a resident AMF suppresses invader success, this effect is time-dependent and a resident will experience reduced growth when invaded. We performed two glasshouse experiments using modified pots, which permitted direct inoculation of resident and invading AMF on the roots. We quantified intraradical AMF abundances using quantitative PCR and visual colonization percentages. We found that both fungi suppressed the invading species and that this effect was strongly dependent on the time lag between inoculations. In contrast to our expectations, neither resident AMF was negatively affected by invasion. We show that order of arrival can influence the abundance of AMF species colonizing a host. These priority effects can have important implications for AMF ecology and the use of fungal inocula in sustainable agriculture.

优先效应（priority effects）指某一物种的抵达对后续群落构建产生的影响，已有研究证实其可调控多种生物的物种组成。目前学界对于丛枝菌根真菌（arbuscular mycorrhizal fungi, AMF）间的优先效应是否会塑造根系真菌群落这一问题，仍缺乏充分认知。本研究针对两种亲缘关系相近的丛枝菌根真菌——根内根孢囊霉*Rhizophagus irregularis*与聚丛球囊霉*Glomus aggregatum*，探究了优先效应是否会影响二者的定殖成功率，并提出三项假说：定居的AMF会抑制入侵物种的定殖、该效应具有时间依赖性、入侵会导致定居AMF的生长量下降。本研究通过改良花盆开展两项温室栽培实验，实现了定居与入侵AMF在植物根系上的直接接种；采用实时荧光定量PCR（quantitative PCR）量化根系内AMF的丰度，并通过视觉计数法统计其定殖百分比。结果显示，两种受试真菌均能抑制入侵物种的定殖，且该抑制效应强烈依赖于两次接种之间的时间间隔。与初始假说相悖的是，两类定居AMF均未因入侵事件受到负面生长影响。本研究证实，物种抵达顺序可调控定殖于宿主植物的AMF物种丰度。这类优先效应对于丛枝菌根真菌生态学研究，以及可持续农业中真菌接种剂的应用均具有重要的理论与实践价值。