Root-colonizing fungi, such as mycorrhizal fungi and dark septate endophyte fungi, are often found on pioneer plant species during early primary succession. However, little is known about which fungal species are responsible for the establishment of pioneer plants when these symbionts colonize simultaneously. We investigated the root-colonizing fungal communities of Pinus thunbergii that established prior to lichens, bryophytes, and short-lived herbaceous plants in a primary successional volcanic mudflow site on Kuchinoerabu Island, Japan. We collected a total of 54 current-year and 1- to 2-year-old seedlings. The colonization of root fungi was evaluated by direct observation of key structures (e.g., mantle, arbuscule, microsclerotia, and hyphae) and molecular analysis. Of the 34 current-year seedlings collected, only 12 individuals were colonized by ectomycorrhizal (ECM) fungi. By contrast, all 1- to 2-year-old seedlings were colonized by ECM fungi. Seedlings colonized by pine-specific ECM fungi, specifically Rhizopogon roseolus and Suillus granulatus, showed higher nitrogen and phosphorus contents in their needles compared to non-ECM seedlings. Arbuscular mycorrhizal fungi and dark septate endophyte fungi were found in only two and three individuals, respectively. The high density of mycophagous deer on Kuchinoerabu-jima may contribute to the favored dispersal of ECM fungi over other root-colonizing fungi. In conclusion, the seedling establishment of P. thunbergii at the volcanic mudflow may be largely supported by ECM fungi, with negligible effects of arbuscular mycorrhizal fungi and dark septate endophytes.

根部定殖真菌，例如菌根真菌和深色有隔内生真菌，经常在早期初级演替过程中在先锋植物物种上发现。然而，当这些共生体同时定殖时，哪些真菌物种负责建立先锋植物却知之甚少。我们研究了日本口永良部岛的一个主要演替火山泥流地点中在地衣、苔藓植物和短命草本植物之前建立的黑松根部定殖真菌群落。我们一共收集了54株当年苗和1-2年生苗。通过直接观察关键结构（例如外套膜、丛枝、微菌核和菌丝）和分子分析来评估根真菌的定殖。在收集的 34 株当年幼苗中，只有 12 株被外生菌根 (ECM) 真菌定植。相比之下，所有 1 至 2 年生的幼苗都被 ECM 真菌定植。与非 ECM 幼苗相比，被松树特有的 ECM 真菌（特别是Rhizopogon Roseolus和Suillus pregnatus）定植的幼苗，其针叶中的氮和磷含量较高。仅在两个和三个个体中分别发现了丛枝菌根真菌和深色隔膜内生真菌。口良部岛上食菌鹿的高密度可能有助于 ECM 真菌比其他根部定殖真菌更容易传播。总之，P的幼苗建立。火山泥流中的thunbergii可能主要由 ECM 真菌支持，丛枝菌根真菌和深色有隔内生菌的影响可以忽略不计。