Table_2_Promiscuity in Lichens Follows Clear Rules: Partner Switching in Cladonia Is Regulated by Climatic Factors and Soil Chemistry.xlsx

Climatic factors, soil chemistry and geography are considered as major factors affecting lichen distribution and diversity. To determine how these factors limit or support the associations between the symbiotic partners, we revise the lichen symbiosis as a network of relationships here. More than one thousand thalli of terricolous Cladonia lichens were collected at sites with a wide range of soil chemical properties from seven biogeographical regions of Europe. A total of 18 OTUs of the algal genus Asterochloris and 181 OTUs of Cladonia mycobiont were identified. We displayed all realized pairwise mycobiont–photobiont relationships and performed modularity analysis. It revealed four virtually separated modules of cooperating OTUs. The modules differed in mean annual temperature, isothermality, precipitation, evapotranspiration, soil pH, nitrogen, and carbon contents. Photobiont switching was strictly limited to algae from one module, i.e., algae of similar ecological preferences, and only few mycobionts were able to cooperate with photobionts from different modules. Thus, Cladonia mycobionts generally cannot widen their ecological niches through photobiont switching. The modules also differed in the functional traits of the mycobionts, e.g., sexual reproduction rate, presence of soredia, and thallus type. These traits may represent adaptations to the environmental conditions that drive the differentiation of the modules. In conclusion, the promiscuity in Cladonia mycobionts is strictly limited by climatic factors and soil chemistry.

气候因子、土壤化学性质与地理环境被视为影响地衣分布与多样性的核心调控因子。为明确上述因子如何限制或维系共生伙伴间的协作关系，本文将地衣共生体系重塑为关联网络展开研究。研究团队从欧洲7个生物地理区的多样土壤化学生境中，采集了逾千株陆生石蕊属（Cladonia）地衣体。经鉴定，共获得星孔藻属（Asterochloris）的18个操作分类单元（Operational Taxonomic Unit，OTU），以及石蕊属真菌共生体的181个OTU。研究人员可视化呈现了所有已证实的真菌共生体-光合共生体两两配对关系，并开展模块化分析，结果揭示出4个相互独立的协作OTU模块。各模块在年平均气温、等温性、降水量、蒸散量、土壤pH值、氮含量与碳含量等环境指标上均存在显著差异。光合共生体的切换仅局限于同一模块内的藻类，即具有相似生态偏好的类群；仅少数真菌共生体可与不同模块的光合共生体形成协作。由此可见，石蕊属真菌共生体通常无法通过切换光合共生体来拓展自身生态位。各模块在真菌共生体的功能性状上亦存在分化，例如有性繁殖率、粉芽（soredia）的有无以及地衣体类型。这些性状或代表了适应驱动模块分化的环境条件的适应性特征。综上，石蕊属地衣真菌共生体的共生宽泛性严格受限于气候因子与土壤化学性质。