Cross-range comparisons reveal reduced dormancy and enhanced growth in alien Iris pseudacorus L.

Understanding cross-range variation in germination and early growth is essential for identifying adaptations and spread mechanisms of invasive plants under global change. Iris pseudacorus is a highly damaging and widespread invasive macrophyte, yet comparative studies between native and non-native populations remain scarce. Here, we examined germination and early growth of populations from one of the species’ native range (Belgium) and a highly invaded Neotropical region (Argentina), and assessed the role of cold stratification as a dormancy-breaking cue. Germination of non-native seeds was 1.5-fold higher than that of native seeds across treatments, with values comparable to those reported for other invaded regions. Cold stratification unexpectedly reduced germination in both ranges, although its effect was stronger for non-native seeds. Belgian seeds showed a 5-fold acceleration of germination following stratification, whereas Argentine seeds germinated rapidly under both treatments, suggesting reduced dormancy and greater germination plasticity in the introduced range. Early growth responses also differed: cold stratified Belgian seeds produced seedlings with slightly more biomass, but without significant differences, while Argentine seeds exhibited significantly higher biomass without stratification, particularly in belowground tissues. These patterns indicate potential incipient shifts in germination timing and early growth strategies following introduction. Our findings highlight the importance of intraspecific variation in early life-history traits for invasion success and underscore the need to integrate these dynamics into future management strategies.