Microbial ecology and activity of snow algae within a Pacific Northwest snowpack

Snow algae blooms are common occurrences in alpine systems and contribute to increasing snow and glacial ice melt rates. Despite the cosmopolitan distribution of snow algae, little is known about the role their life cycle plays in community composition and activity in snowpack. Mount Baker, in Washington, USA, is a rapidly changing alpine ecosystem. Here we present estimates of cellular biomass, microbial community composition, and primary productivity measurements associated with surficial snow algae blooms and a vertical profile within a snow pit to characterize the microbial ecology of this snowpack system. Chloromonas was the most abundant algae detected in our samples. Sphingobacteriaceae were the most dominant bacteria in samples where fungi were the most abundant eukaryote, whereas Chitinophagaceae dominated when Chlorophyceae were the most abundant eukaryote. In a snow pit vertical profile, we observed more algae in the green-pigmented, flagellated life cycle stage at depth (~30 cm below the surface) than at the surface where the astaxanthin-rich, aplanospore life cycle stage dominated. Higher resolution analyses revealed that Chloromonas-associated photosynthesis transcripts were more abundant at depth than at the surface of the snowpack. These results suggest that there is a photosynthetic niche within alpine snowpack that has unknown effects on the carbon budget and provides potentially undetected primary productivity resulting in a “cryptic” photosynthetic system.雪藻暴发（snow algae blooms）在高山生态系统中极为常见，且可加速积雪与冰川冰的消融速率。尽管雪藻（snow algae）具有广布的地理分布，但学界对其生命周期在积雪层群落组成与代谢活动中所扮演的角色仍知之甚少。美国华盛顿州的贝克山（Mount Baker）是一处快速演变的高山生态系统。本研究以该积雪层系统的微生物生态学特征为研究目标，针对表层雪藻暴发区域以及一处雪坑内的垂直剖面，开展了细胞生物量、微生物群落组成以及初级生产力的测定与估算工作。梭罗藻属（Chloromonas）是本研究样本中检出丰度最高的藻类。在真菌为优势真核生物的样本中，鞘氨醇杆菌科（Sphingobacteriaceae）为优势细菌类群；而当绿藻纲（Chlorophyceae）为优势真核生物时，几丁质杆菌科（Chitinophagaceae）则占据主导地位。在雪坑垂直剖面中，我们在积雪表层下约30厘米的深度处，观察到更多处于绿色色素型鞭毛体生命周期阶段的藻类；而积雪表层则以富含虾青素的不动孢子生命周期阶段占据主导。更高分辨率的分析结果显示，与梭罗藻属（Chloromonas）相关的光合作用转录本在积雪深层的丰度高于表层。上述结果表明，高山积雪层中存在一处光合生态位，其对碳收支的影响尚未明确，且该生态位可产生尚未被探明的初级生产力，进而形成一套“隐秘”光合系统。