Detection of an invasive aquatic plant in natural water bodies using environmental DNA

The ability to detect founding populations of invasive species or rare species with low number of individuals is important for aquatic ecosystem management. Traditional approaches use historical data, knowledge of the species’ ecology and time-consuming surveys. Within the past decade, environmental DNA (eDNA) has emerged as a powerful additional tracking tool. While much work has been done with animals, comparatively very little has been done with aquatic plants. Here we investigated the transportation and seasonal changes in eDNA concentrations for an invasive aquatic species, Elodea canadensis, in Norway. A specific probe assay was developed using chloroplast DNA to study the fate of the targeted eDNA through space and time. The spatial study used a known source of Elodea canadensis within Lake Nordbytjern 400 m away from the lake outlet flowing into the stream Tveia. The rate of disappearance of E. canadensis eDNA was an order of magnitude loss over about 230 m in the lake and 1550 m in the stream. The time series study was performed monthly from May to October in lake Steinsfjorden harbouring E. canadensis, showing that eDNA concentrations varied by up to three orders of magnitude, peaking during fall. In both studies, the presence of suspended clay or turbidity for some samples did not hamper eDNA analysis. This study shows how efficient eDNA tools may be for tracking aquatic plants in the environment and provides key spatial and temporal information on the fate of eDNA.精准检出入侵物种或个体稀少的稀有物种的初始种群，对水生生态系统管理具有重要意义。传统研究方法多依赖历史资料、物种生态学知识以及耗时耗力的野外调查。近十年来，环境DNA（environmental DNA，简称eDNA）作为一种高效的新型监测工具逐渐兴起。尽管学界已针对动物开展了大量eDNA相关研究，但针对水生植物的相关工作却相对匮乏。本研究以挪威的入侵水生物种加拿大伊乐藻（Elodea canadensis）为研究对象，探究了其eDNA的迁移规律与浓度的季节变化特征。研究团队依托叶绿体DNA（chloroplast DNA）开发了特异性探针检测技术，以解析目标eDNA的时空归趋。空间分布研究选取了诺德比滕湖（Lake Nordbytjern）内的已知加拿大伊乐藻种群作为采样源，该种群距离汇入特维亚河（Tveia）的湖出水口约400米。研究发现，加拿大伊乐藻eDNA的降解速率在湖内约230米范围内、溪流内约1550米范围内均呈现一个数量级的衰减。时序监测研究于5月至10月每月对栖息有加拿大伊乐藻的斯泰因峡湾湖（Lake Steinsfjorden）开展采样，结果显示eDNA浓度的变化幅度可达三个数量级，并于秋季达到峰值。两项研究均证实，部分样品中存在的悬浮黏土或浊度并不会对eDNA检测分析造成干扰。本研究证实了eDNA技术在水生植物环境监测中的高效性，并为解析eDNA的时空归趋提供了关键数据支撑。