Biological soil crusts as unique microecosystem represent a suitable model system to address taxonomy and cryptic diversity of microalgal key players

在全球范围内，生物土壤结皮(BSC)是干旱和其他极端地区最具生产力的微生物生物量，各种微藻类群是关键成分。生物干细胞是由不同的生物体及其副产物组成的微生态系统，在土壤的初级生产、固氮、矿化、保水和稳定等方面发挥着重要的生态功能。微藻的系统学目前正在从形态系统学向分子系统发育种概念转变。形态概念受到了很多批评，因为潜在的生物体往往缺乏明显的形态特征。因此，这两个系统在分类分类和物种划界方面存在分歧：这是一个需要解决的根本问题。在世界各地的BSCs中都可以发现微藻属球藻和球藻，这表明它们在生态上起着关键作用。然而，它们的分类仍然没有解决，这阻碍了例如任何生物多样性的估计。球孢子菌和球孢子菌的修订涉及SPP 1991 Taxon-Omics中的两个主要目标：i.物种的发现和定界；ii.加快命名过程并生成识别工具、分类、物种清单或专著。以现代算法分析的分子数据为基础，以形态、生态生理和生化特征为支持的多相方法将导致强大的分类学以及新物种的发现和定义。因此，将对来自培养收藏的现有菌株进行排序，并将沿着波罗的海沿海沙丘的梯度从BSC中分离出各自属的新菌株。如果缺失，将对高度可变的ITS区和叶绿体标记rbcL进行测序。基于这些数据，将计算系统发育树，并将应用现代物种划分算法(如GYMC和PTP)。结果将得到化学分类标记(低分子碳水化合物)、生境信息、生态生理和形态特征的支持。这种多相方法将为球孢菌属和球孢菌属的分类修订提供强有力的证据，从而通过定义物种限制来加快命名过程；将描述新种，并在必要时合并形态种。对于未来的研究，将开发一种基于下一代测序的条形码工具，从而能够快速而准确地估计生物干细胞中的两种重要关键生物：球孢子虫和链球菌。

On a global scale, biological soil crusts (BSC) are the most productive microbial biomass in arid and other extreme regions with various microalgal taxa as key components. BSCs are formed by different living organisms and their by-products, creating a microecosystem that exerts ecologically important, multi-functional roles in primary production, nitrogen fixation, mineralization, water retention and stabilization of soils. The systematics of microalgae is currently changing from a morphological to a molecular phylogenetic species concept. The morphological concept received a lot of criticism because the underlying organisms often lack distinct morphological characters. Therefore, both systems disagree in taxonomical classification and species delimitation: a fundamental problem that needs to be addressed. The microalgal genera Coccomyxa and Stichococcus can be found in BSCs all over the world, indicating ecological key functions. However, their taxonomy is still not resolved, which hamper, for example, any biodiversity estimation. The revision of Coccomyxa and Stichococcus addresses two points of the overarching goals within the SPP 1991 Taxon-Omics: I. discovery and delimitation of species; II. speeding up the naming process and generating identification tools, classifications, species inventories, or monographs. A polyphasic approach based on molecular data analyzed by modern algorithms and supported by morphological, ecophysiological and biochemical characteristics will result in a robust taxonomy as well as in the discovery and definition of new species. Therefore, existing strains from culture collections will be ordered and new strains of the respective genera will be isolated from BSCs along a gradient of coastal dunes at the Baltic Sea. Where missing, the highly variable ITS region and the chloroplast marker rbcL will be sequenced. Based on these data phylogenetic trees will be calculated and modern algorithms (like GYMC and PTP) for species delimitation will be applied. The results will be supported by chemotaxonomic markers (low molecular weight carbohydrates), habitat information, ecophysiological and morphological characteristics. This polyphasic approach will give strong evidence for a taxonomic revision of Coccomyxa and Stichococcus, thereby speeding up the naming process by defining species limits; new species will be described and, if necessary, morphological species merged. For future studies a barcode tool based on next-generation sequencing will be developed that allows a rapid and precise biodiversity estimation of the two important key organisms in BSCs: Coccomyxa and Stichococcus.