Communities of Endophytic Sebacinales Associated with Roots of Herbaceous Plants in Agricultural and Grassland Ecosystems Are Dominated by <i>Serendipita herbamans</i> sp. nov

Endophytic fungi are known to be commonly associated with herbaceous plants, however, there are few studies focusing on their occurrence and distribution in plant roots from ecosystems with different land uses. To explore the phylogenetic diversity and community structure of Sebacinales endophytes from agricultural and grassland habitats under different land uses, we analysed the roots of herbaceous plants using strain isolation, polymerase chain reaction (PCR), transmission electron microscopy (TEM) and co-cultivation experiments. A new sebacinoid strain named Serendipita herbamans belonging to Sebacinales group B was isolated from the roots of Bistorta vivipara, which is characterized by colourless monilioid cells (chlamydospores) that become yellow with age. This species was very common and widely distributed in association with a broad spectrum of herbaceous plant families in diverse habitats, independent of land use type. Ultrastructurally, the presence of S. herbamans was detected in the cortical cells of Plantago media, Potentilla anserina and Triticum aestivum. In addition, 13 few frequent molecular operational taxonomic units (MOTUs) or species were found across agricultural and grassland habitats, which did not exhibit a distinctive phylogenetic structure. Laboratory-based assays indicate that S. herbamans has the ability to colonize fine roots and stimulate plant growth. Although endophytic Sebacinales are widely distributed across agricultural and grassland habitats, TEM and nested PCR analyses reinforce the observation that these microorganisms are present in low quantity in plant roots, with no evidence of host specificity.内生真菌（endophytic fungi）通常被认为与草本植物广泛共生，但目前针对不同土地利用类型生态系统中植物根系内其发生与分布的研究仍较为匮乏。为探究不同土地利用模式下农业与草地生境中蜡壳耳目（Sebacinales）内生真菌的系统发育多样性与群落结构，我们采用菌株分离、聚合酶链式反应（polymerase chain reaction, PCR）、透射电子显微镜（transmission electron microscopy, TEM）以及共培养实验，对草本植物根系开展了分析。从拳参（Bistorta vivipara）的根系中分离得到一株隶属于蜡壳耳目B群的新型类蜡壳菌菌株，命名为Serendipita herbamans，其特征为无色串生细胞（厚垣孢子），随培养时长增加会逐渐变黄。该物种分布广泛且极为常见，可与多样生境中广谱的草本植物科属形成共生关系，不受土地利用类型的限制。超微结构观察显示，S. herbamans可定植于长叶车前（Plantago media）、鹅绒委陵菜（Potentilla anserina）以及普通小麦（Triticum aestivum）的皮层细胞内。此外，在农业与草地生境中共发现13个较为常见的分子操作分类单元（molecular operational taxonomic units, MOTUs）或物种，此类类群未表现出独特的系统发育结构。室内培养实验结果表明，S. herbamans能够定植植物细根并促进植物生长。尽管蜡壳耳目内生真菌广泛分布于农业与草地生境中，但透射电镜与巢式PCR（nested PCR）分析证实，这类微生物在植物根系内的丰度较低，且未表现出宿主特异性。