Fungi are an important, yet often, neglected component of the aquatic microflora, and is responsible for primary decomposition and further processing of organic matter. By comparison, the ecological roles of terrestrial fungi have been well-studied, but the diversity and function of fungi that populate aquatic environments remain poorly understood. Here, the impact of urbanization on fungal diversity and community composition in the canal system of Suzhou was assessed by sequencing the internal transcribed spacer 1 (ITS1) region of the rRNA operon. It was amplified from environmental DNA that has been extracted from water samples and pre-deployed decomposing leaves collected from nine sampling locations (high, medium and low urbanization) over two seasons. The fungal diversity and community composition were determined by bioinformatic analysis of the large DNA sequence datasets generated to identify operational taxonomic units (OTUs) for phylogenetic assignment; over 1 million amplicons were sequenced from 36 samples. The alpha-diversity estimates showed high differences in fungal diversity between water and leaf samples, and winter versus summer. Higher numbers of fungal OTUs were identified in both water and leaf samples collected in the summer, and fungal diversity was also generally higher in water than on colonized leaves in both seasons. The fungal community on leaves was usually dominated by Ascomycetes, especially in winter, while water samples contained more diversity at phylum level with Chytridiomycetes often prominent, particularly in summer. At a genus level, a very high relative abundance of Alternaria on leaves was observed in winter at all locations, in contrast to very low abundance of this genus across all water samples. Fungal community composition also varied between sampling locations (i.e., urbanization); in cluster analysis, samples from high urbanization locations formed a distinct cluster, with medium and low urbanization samples clustering together or in some instances, separately. Redundancy analysis shed further light on the relationships between variation in fungal community composition and water physico-chemical properties. Fungal community diversity variation and correlation with different parameters is discussed in detail, but overall, the influence of season outweighed that of urbanization. This study is significant in cataloguing the impact of urbanization on fungal diversity to inform future restoration of urban canal systems on the importance of protecting the natural aquatic fungal flora.

中文翻译：

---

城市化梯度下淡水运河真菌群落结构的变化

真菌是水生微生物群落中一个重要但经常被忽视的组成部分，负责有机物的初级分解和进一步加工。相比之下，陆生真菌的生态作用已得到充分研究，但对生活在水生环境中的真菌的多样性和功能知之甚少。在这里，城市化对苏州运河系统真菌多样性和群落组成的影响是通过对 rRNA 操纵子的内部转录间隔区 1 (ITS1) 区域进行测序来评估的。它是从环境 DNA 中扩增而来的，这些 DNA 是从两个季节的九个采样地点（高、中和低城市化）收集的水样和预先部署的腐烂叶子中提取的。真菌多样性和群落组成是通过对生成的大型 DNA 序列数据集的生物信息学分析来确定的，以识别用于系统发育分配的操作分类单元 (OTU)；从 36 个样本中测序了超过 100 万个扩增子。α 多样性估计表明，水样和叶样之间以及冬季与夏季之间的真菌多样性存在很大差异。在夏季收集的水样和叶子样品中都发现了更多数量的真菌 OTU，并且两个季节水中的真菌多样性也普遍高于定植叶子。叶片上的真菌群落通常以子囊菌为主，尤其是在冬季，而水样在门水平上包含更多的多样性，壶菌通常很突出，尤其是在夏季。在属水平上，冬季在所有地点都观察到叶上链格孢属的相对丰度非常高，而在所有水样中该属的丰度非常低。采样地点（即城市化）之间的真菌群落组成也不同；在聚类分析中，来自高度城市化地区的样本形成了一个独特的聚类，中度和低度城市化样本聚集在一起或在某些情况下分别聚集在一起。冗余分析进一步阐明了真菌群落组成变化与水理化性质之间的关系。详细讨论了真菌群落多样性的变化及其与不同参数的相关性，但总体而言，季节的影响大于城市化的影响。