ABSTRACT
Seagrass meadows are among the most threatened ecosystems worldwide, facing multiple anthropogenic stressors that often occur in succession. While plant-physiological responses to multiple stressors are well documented, the role of microbial symbionts in mediating consecutive stressors events remains poorly understood. Using a mesocosm experiment, Zostera marina (eelgrass) was exposed to sequential stressors: nutrient enriched sediments (NE; 70 mg of total N per 100 gDW sediment-1 for 28 days), followed by a simulated marine heatwave (MHW, 23.3°C for 15 days) and subsequent storm event (25 cm/s flow, 12 days).
Nutrient enrichment resulted in a microbiome shift, specifically a 49.2-fold enrichment of sulfur-oxidizing Arcobacteraceae and a 4.7-fold increase in Sulfurimonadaceae, suggesting possible microbiome-mediated responses mitigating sulfide toxicity. In contrast, warming responses were primarily physiological: aboveground biomass increased by 41.5% and net production increased by 37.1% (mg FW shoot-1 day-1), with synergistic effects under combined enrichment and heat stress (up to 175% higher production), indicating that temperature outweighs nutrient stress. Storm exposure triggered a 114% increase in belowground biomass via root elongation, which increases the resilience of these plants to higher flow velocities, but this acclimation was diminished by 51% in plants previously exposed to the MHW, indicating environmental legacy effects.
Our results demonstrate that eelgrass resilience depends critically on stressors sequence, where legacy effects alter both plant-microbe interactions and physiological responses.These findings emphasize the need to incorporate both a consecutive-stressor approach and microbiome dynamics into seagrass research and conservation strategies under climate change.
DOI: 10.1016/j.marenvres.2025.107748
