MULTIPLE STRESSOR INTERACTIONS DRIVE UNPREDICTABLE PHYSIOLOGICAL RESPONSES IN SUBMERGED MACROPHYTES

Submerged macrophytes are central to freshwater ecosystem functioning but are declining globally under multiple anthropogenic stressors. We systematically reviewed 12,858 publications and extracted effect sizes from 124 experiments to identify general patterns in physiological responses and interaction types. Additive effects dominated (50%), indicating that accumulated stressors generally cause negative, but not necessarily amplified, responses. Synergistic interactions were relatively infrequent (14%) despite theoretical expectations of prevalence, though the limited number of experiments testing more than two stressors suggests their frequency may be underestimated. Most studies examined combinations of nutrient enrichment, shading, toxic trace metals, warming, and emerging contaminants such as PFAS and microplastics, typically under simplified 2×2 factorial laboratory designs. Antagonistic interactions often reflected dominance of a single stressor or compensatory responses, whereas synergisms were most frequent with metals combined with co-stressors enhancing bioavailability. Geographic and taxonomic biases were evident, with reliance on a few species and short-term assays. To improve mechanistic understanding, we propose Stuckenia pectinata as a model organism due to its cosmopolitan distribution, experimental tractability, and newly available genomic resources, enabling integration of physiological, molecular, and microbiome approaches. Expanding stressor complexity, experimental duration, and taxonomic breadth will strengthen predictions of macrophyte responses and inform freshwater conservation under global change.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Amine Mohamed Mahdjoub, Humboldt-Universität zu Berlin (amine.mahdjoub@igb-berlin.de)

Authors:

Amine Mahdjoub, Leibniz Institute of Freshwater Ecology and Inland Fisheries  (amine.mahdjoub@igb-berlin.de)

Severin Eispanier, Kiel University  (s.einspanier@phytomed.uni-kiel.de)

Elisabeth Gross, Université de Lorraine  (gross5@univ-lorraine.fr)

Sabine Hilt, Leibniz Institute of Freshwater Ecology and Inland Fisheries  (sabine.hilt@igb-berlin.de)