Data_Sheet_1_Terrestrial Inputs Shape Coastal Bacterial and Archaeal Communities in a High Arctic Fjord (Isfjorden, Svalbard).PDF

The Arctic is experiencing dramatic changes including increases in precipitation, glacial melt, and permafrost thaw, resulting in increasing freshwater runoff to coastal waters. During the melt season, terrestrial runoff delivers carbon- and nutrient-rich freshwater to Arctic coastal waters, with unknown consequences for the microbial communities that play a key role in determining the cycling and fate of terrestrial matter at the land-ocean interface. To determine the impacts of runoff on coastal microbial (bacteria and archaea) communities, we investigated changes in pelagic microbial community structure between the early (June) and late (August) melt season in 2018 in the Isfjorden system (Svalbard). Amplicon sequences of the 16S rRNA gene were generated from water column, river and sediment samples collected in Isfjorden along fjord transects from shallow river estuaries and glacier fronts to the outer fjord. Community shifts were investigated in relation to environmental gradients, and compared to river and marine sediment microbial communities. We identified strong temporal and spatial reorganizations in the structure and composition of microbial communities during the summer months in relation to environmental conditions. Microbial diversity patterns highlighted a reorganization from rich communities in June toward more even and less rich communities in August. In June, waters enriched in dissolved organic carbon (DOC) provided a niche for copiotrophic taxa including Sulfitobacter and Octadecabacter. In August, lower DOC concentrations and Atlantic water inflow coincided with a shift toward more cosmopolitan taxa usually associated with summer stratified periods (e.g., SAR11 Clade Ia), and prevalent oligotrophic marine clades (OM60, SAR92). Higher riverine inputs of dissolved inorganic nutrients and suspended particulate matter also contributed to spatial reorganizations of communities in August. Sentinel taxa of this late summer fjord environment included taxa from the class Verrucomicrobiae (Roseibacillus, Luteolibacter), potentially indicative of a higher fraction of particle-attached bacteria. This study highlights the ecological relevance of terrestrial runoff for Arctic coastal microbial communities and how its impacts on biogeochemical conditions may make these communities susceptible to climate change.

北极正经历剧烈变化，包括降水增加、冰川消融与多年冻土解冻，由此导致向近岸水域输入的淡水径流量持续攀升。融季期间，陆地径流将富含碳与营养盐的淡水输送至北极近岸水域，但其对在陆-海界面调控陆地物质循环与归宿过程中发挥关键作用的微生物群落所产生的影响尚不明确。为探明径流对沿岸微生物（细菌与古菌）群落的影响，我们于2018年在斯瓦尔巴群岛（Svalbard）的伊斯峡湾（Isfjorden）系统中，探究了融季早期（6月）与晚期（8月）之间远洋微生物群落结构的变化。我们从沿峡湾断面采集的水柱、河流与沉积物样本中扩增得到16S核糖体RNA（16S rRNA）基因的扩增子序列，采样断面覆盖了从浅水河口、冰川前缘至峡湾外海的区域。我们结合环境梯度对群落结构的变化展开分析，并将其与河流及海洋沉积物微生物群落进行比对。本研究发现，夏季月份中，微生物群落的结构与组成随环境条件发生了显著的时空重构。微生物多样性模式显示，群落从6月的物种丰富度较高的群落逐步重构为8月的更为均匀且丰富度更低的群落。6月时，溶解有机碳（dissolved organic carbon, DOC）富集的水域为包括硫化杆菌属（Sulfitobacter）与十八杆菌属（Octadecabacter）在内的富营养型类群提供了生态位。8月时，溶解有机碳浓度降低与大西洋水输入共同促使群落转向更常见于夏季层化期的广布类群（如SAR11进化枝Ia），以及占优势的贫营养型海洋进化枝（OM60、SAR92）。更高的河流溶解无机营养盐与悬浮颗粒物输入，同样促成了8月群落的空间重构。该晚夏峡湾环境的指示类群包括疣微菌纲（Verrucomicrobiae）下的玫瑰芽孢杆菌属（Roseibacillus）与黄体杆菌属（Luteolibacter），这可能预示着附着于颗粒物的细菌占比更高。本研究凸显了陆地径流对北极沿岸微生物群落的生态学意义，以及其对生物地球化学环境的影响可能使这些群落易受气候变化影响。