Data from: Topology of tree-mycorrhizal fungus interaction networks in xeric and mesic Douglas-fir forests

1. From the phytocentric perspective, a mycorrhizal network (MN) is formed when the roots of two or more plants are colonized by the same fungal genet. MNs can be modelled as interaction networks with plants as nodes and fungal genets as links. The potential effects of MNs on facilitation or competition between plants are increasingly recognized, but their network topologies remain largely unknown. This information is needed to understand the ecological significance of MN functional traits. 2. The objectives of this study were to describe the interaction network topologies of MNs formed between two ectomycorrhizal fungal species, Rhizopogon vesiculosus and R. vinicolor, and interior Douglas-fir trees at the forest stand scale, identify factors leading to this structure and to contrast MN structures between forest plots with xeric versus mesic soil moisture regimes. 3. Tuberculate mycorrhizas were sampled in six 10 × 10 m plots with either xeric or mesic soil moisture regimes. Microsatellite DNA markers were used to identify tree and fungal genotypes isolated from mycorrhizas and for comparison with reference tree boles above-ground. 4. In all six plots, trees and fungal genets were highly interconnected. Size asymmetries between different tree cohorts led to non-random MN topologies, while differences in size and connectivity between Rhizopogon species-specific subnetwork components contributed towards MN nestedness. Large mature trees acted as network hubs with a significantly higher node degree compared to smaller trees. MNs representing trees linked by R. vinicolor genets were mostly nested within larger, more highly connected R. vesiculosus-linked MNs. 5. Attributes of network nodes showed that hub trees were more important to MN topology on xeric than mesic sites, but the emergent structures of MNs were similar in the two soil moisture regimes. 6. Synthesis. This study suggests MNs formed between interior Douglas-fir trees and R. vesiculosus and R. vinicolor genets are resilient to the random loss of participants, and to soil water stress, but may be susceptible to the loss of large trees or fungal genets. Our results regarding the topology of MNs contribute to the understanding of forest stand dynamics and the resilience of forests to stress or disturbance.

1. 从植物中心视角（phytocentric perspective）出发，当两株及以上植物的根系被同一真菌遗传株系（fungal genet）定植后，即形成菌根网络（mycorrhizal network, MN）。菌根网络可被建模为以植物为节点、真菌遗传株系为连接边的互作网络。学界已逐渐认识到菌根网络对植物间促进或竞争作用的潜在调控效应，但此类网络的拓扑结构仍鲜为人知。而要解析菌根网络功能性状的生态学意义，此类观测数据必不可少。
2. 本研究的核心目标为：在林分尺度下，刻画由两种外生菌根真菌（ectomycorrhizal fungal species）——泡囊须腹菌（Rhizopogon vesiculosus）与酒红须腹菌（R. vinicolor）——与内陆花旗松（interior Douglas-fir）树木构建的菌根网络的互作拓扑结构，解析驱动该结构形成的影响因子，并对比旱生（xeric）与中生（mesic）土壤水分样地中菌根网络结构的差异。
3. 研究人员在6块10×10 m的样地中采集结节状菌根（tuberculate mycorrhizas），这些样地的土壤水分状况分别为旱生或中生。本研究采用微卫星DNA标记（microsatellite DNA markers）技术，对从菌根样本中分离得到的林木与真菌基因型进行鉴定，并与地上参考树干的基因型进行比对。
4. 在全部6块样地中，林木与真菌遗传株系均呈现高度连通的特征。不同同龄林木组间的大小不对称性，使得菌根网络呈现非随机拓扑结构；而须腹菌属物种特异性子网组件间的大小与连通性差异，则促成了菌根网络的嵌套性（nestedness）。大型成熟林木作为网络枢纽（network hubs），其节点度（node degree）显著高于小型林木。由酒红须腹菌遗传株系连接的菌根网络，大多嵌套于连通性更强、规模更大的泡囊须腹菌关联菌根网络之中。
5. 网络节点属性分析结果显示，相较于中生土壤样地，枢纽林木在旱生样地中对菌根网络拓扑结构的贡献更为关键，但两种土壤水分状况下菌根网络的涌现结构（emergent structures）并无显著差异。
6. 综合与讨论。本研究表明，由内陆花旗松与泡囊须腹菌、酒红须腹菌遗传株系形成的菌根网络，既对参与者的随机丢失具有较强抗性，也可耐受土壤水分胁迫，但可能因大型林木或真菌遗传株系的丢失而遭受破坏。本研究关于菌根网络拓扑结构的成果，有助于深化对林分动态以及森林应对胁迫或干扰的抗性机制的理解。