Growth Response of Cuttings to Drought and Intermittent Flooding for Three Salix Species and Implications for Riverbank Soil Bioengineering

Willows are used as cuttings or in fascines for riverbank soil bioengineering, to control erosion with their high resprouting ability and rapid growth. However, water availability is highly variable along riverbanks both in time and space and constitutes a major stress limiting willow establishment. A species-specific understanding of willow cutting response to water stress is critical to design successful riverbank soil bioengineering projects given exclusive use of local species is often recommended. In a three-month greenhouse experiment, we investigated the effects of three soil moisture treatments (drought-soil saturation-intermittent flooding) on survival, biomass production and root growth of cuttings of three willow species used for soil bioengineering along NE American streams (Salix discolor-S. eriocephala-S. interior). Cutting survival was high for all species and treatments (>89%). Biomass production and root volume only differed between species. S. eriocephala produced the highest biomass and root volume, and S. discolor invested more in belowground than aboveground biomass. Root length responded to soil moisture differently between species. Under intermittent flooding, S. eriocephala produced shorter roots, while S. interior produced longer roots. For riverbank soil bioengineering, S. eriocephala should be favored at medium elevation and S. interior at lower elevation.

Quantification of Saprolegnia parasitica in river water using real-time quantitative PCR: from massive fish mortality to tap drinking water

Since 2010, the Loue River (Franche-Comté, East of France) has been suffering from massive fish kills infested by Saprolegnia parasitica. The river supplies inhabitants of the city of Besançon in drinking water, raising the question of a potential risk through both water consumption and use. We developed a real-time quantitative PCR (qPCR) to quantify S. parasitica in the Loue River as well as in the drinking water. A weak spatial trend is suggested with greater quantities of S. parasitica observed at the sampling station close to the main pumping station. No S. parasitica DNA was detected in the tap water connected to pumping stations. The use of qPCR, which combines specificity, practicality, speed and reliability, appears to be an effective tool to monitor the spatial and temporal dynamics of this oomycete and identify the risk period for wild salmonid populations in the field, for fishery management or in aquaculture.