Intraspecific Variation in Seed Germination Strategies of Alopecurus myosuroides (Blackgrass; Poaceae) Across Climatic Gradients

ABSTRACT Intraspecific variation in seed germination traits can strongly influence weed persistence and spread, yet its relationship with climate remains poorly resolved. We quantified population‐level variation in germination temperature and water requirements, germination speed and synchrony and seed mass in 12 Alopecurus myosuroides populations from contrasting macroclimatic regions across Europe and West Asia. To minimize maternal environmental effects, all seeds were produced under common‐garden conditions. Germination assays across controlled temperature and water‐potential gradients revealed restricted variation in lower and upper thermal limits, whereas the thermal optimum and water‐potential thresholds varied among populations, with no consistent association with macroclimatic variables. In contrast, germination speed, synchrony and seed mass showed clear geographic structuring: populations from colder and wetter regions germinated faster and more synchronously and produced heavier seeds, whereas populations from warmer and more seasonal regions germinated more slowly, less synchronously and produced smaller seeds. Multivariate analyses confirmed that geographic and climatic variation aligned primarily with germination dynamics and seed mass rather than with hydrothermal germination limits. These results indicate that population differentiation in A. myosuroides is expressed mainly through variation in the timing, coordination and vigour of early establishment rather than through divergence in physiological germination thresholds. For weed management, regional differences in emergence dynamics are therefore likely to influence the effectiveness of cultural and chemical control measures: rapid and synchronous emergence in colder, wetter systems may reduce the efficacy of delayed sowing or stale seedbeds, whereas slower and more asynchronous emergence in warmer, seasonal regions may increase escape from pre‐emergence control. Accounting for population‐level variation in germination dynamics is thus important for designing effective, regionally adapted management strategies for A. myosuroides .