Scheidegger Christoph
Biodiversity and Conservation Biology, Swiss Federal Institute for Forest, Snow and Landscape Research, WSL, Zürcherstr. 111, Birmensdorf, CH-8903, Switzerland.
Mol Ecol. 2016 Jul;25(14):3261-3. doi: 10.1111/mec.13710.
During the evolution of the lichen symbiosis, shifts from one main type of photobiont to another were infrequent (Miadlikowska et al. ) but some remarkable transitions from green algal to diazotrophic cyanobacterial photobionts are known from unrelated fungal clades within the ascomycetes. Cyanobacterial, including tripartite, associations (green algal and cyanobacterial photobionts in one lichen individual) facilitate these holobionts to live as C- and N-autotrophs. Tripartite lichens are among the most productive lichens, which provide N-fertilization to forest ecosystems under oceanic climates (Peltigerales) or deliver low, but ecologically significant N-input into subarctic and alpine soil communities (Lecanorales, Agyriales). In this issue of Molecular Ecology, Schneider et al. (2016) mapped morphometric data against an eight-locus fungal phylogeny across a transition of photobiont interactions from green algal to a tripartite association and used a phylogenetic comparative framework to explore the role of nitrogen-fixing cyanobacteria in size differences in the Trapelia-Placopsis clade (Agyriales). Within the group of tripartite species, the volume of cyanobacteria-containing structures (cephalodia) correlates with thallus thickness in both phylogenetic generalized least squares and phylogenetic generalized linear mixed-effects analyses, and the fruiting body core volume increased ninefold. The authors conclude that cyanobacterial symbiosis appears to have enabled lichens to overcome size constraints in oligotrophic environments such as rock surfaces. The Trapelia-Placopsis clade analyzed by Schneider et al. (2016) is an exciting example of interactions between ecology, phylogeny and lichen biology including development - from thin crustose green algal microlichens to thick placodioid, tripartite macrolichens: as thick as three in a bed (Scott ).
在地衣共生的进化过程中，从一种主要的光合生物类型转变为另一种的情况并不常见（米亚德利科夫斯卡等人），但在子囊菌门内不相关的真菌类群中，已知有一些从绿藻光合生物到固氮蓝藻光合生物的显著转变。包括三方共生（一个地衣个体中有绿藻和蓝藻光合生物）在内的蓝藻共生，使这些共生体能够作为碳和氮自养生物生存。三方地衣是生产力最高的地衣之一，在海洋性气候下为森林生态系统提供氮素施肥（皮壳衣目），或为亚北极和高山土壤群落提供少量但具有生态意义的氮输入（茶渍目、石耳目）。在本期《分子生态学》中，施耐德等人（2016年）将形态测量数据与跨越从绿藻光合生物到三方共生转变的八个基因座的真菌系统发育图谱进行比对，并使用系统发育比较框架来探究固氮蓝藻在 Trapelia - Placopsis 类群（石耳目）大小差异中的作用。在三方物种组中，在系统发育广义最小二乘法和系统发育广义线性混合效应分析中，含蓝藻结构（头状体）的体积与叶状体厚度相关，并且子实体核心体积增加了九倍。作者得出结论，蓝藻共生似乎使地衣能够克服在贫营养环境如岩石表面的大小限制。施耐德等人（2016年）分析的 Trapelia - Placopsis 类群是生态学、系统发育学和地衣生物学（包括从薄壳状绿藻微地衣到厚盘状、三方大型地衣的发育）之间相互作用的一个令人兴奋的例子：在床上厚达三英寸（斯科特）。
