A Link Between Plant Stress and Hydrodynamics? Indications From a Freshwater Macrophyte

• Published in: Water resources research Vol. 57; no. 9
• Main Authors: Vettori, D., Niewerth, S., Aberle, J., Rice, S. P.
• Format: Journal Article
• Language: English
• Published: 01.09.2021
• Subjects: biomechanics; chlorophyll fluorescence; drag force; flow‐vegetation interactions; freshwater macrophyte
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2021WR029618

Live plants are increasingly used in hydraulic laboratories to investigate flow‐vegetation interactions. In such experiments, they are often exposed to stressful handling and storage that can cause strong physiological responses and modifications in plant biomechanics. Little is known about the potential effect of these impacts on the performance of plants during hydraulic experiments. In this multidisciplinary study with a freshwater macrophyte (Potamogeton natans) we assess whether the duration and the conditions in which plants are stored in a laboratory prior to testing can impact plant stress, biomechanics and hydrodynamics, and quantify this impact. Plant stress was evaluated using chlorophyll fluorescence analysis (and the maximum quantum yield of photosystem II as specific indicator). Plant hydrodynamics were assessed using the drag coefficient calculated from drag force measurements at two flow scenarios. The results show that different plant handling/storage procedures can have a significant impact on plant hydrodynamics even within a short time frame, with a variation of the mean drag coefficient of approximately 30% across groups, which is comparable to the variation found across different species of freshwater macrophytes in previous studies. Plants with the highest level of stress were also characterized by the lowest drag coefficient across the groups considered, suggesting a potential link between plant stress and hydrodynamics. Plain Language Summary Aquatic plants are used in laboratory experiments designed to understand how they affect water velocity, sediment movement and the distribution of substances in the water. Plants are moved from the field or nursery to the laboratory, where the light conditions are often insufficient for photosynthesis and the water quality can be poor; this can lead to deterioration in plant health and cause plants to physically change. Here we use a common aquatic plant to investigate how such changes can affect the force associated with the water flow that pulls the plant downstream (drag force). To measure plant health, we used an indicator of photosynthesis efficiency, to measure plant rigidity we conducted bending tests on plant stems, and to measure the drag force on the plant we carried out tests in a channel equipped with a force sensor. The results show that the drag force experienced by plants depends on how, and for how long, they have been stored and that stressed plants are better at avoiding some of the drag force. This has implications for scientists who use live plants in laboratory experiments, indicating that storage and handling prior to experiments can have a significant effect on the results. Key Points The hydrodynamics of freshwater macrophytes can be affected by the conditions in the field and storage procedure used prior to experiments This impact is quantified as up to 30% of the drag coefficient, similar to the impact associated with using different macrophyte species Higher levels of plant stress are associated with lower drag forces