Predicting responses of plants to abiotic stress is a key challenge in ecology. Here we examined climate-related mechanisms regulating seeds germination. Our objectives were to assess germination traits and temperature responses in populations collected along a climatic gradient and to test for evidence of clinal variation in germination traits. Nine populations of Amaranthus albus, a noxious weed, were collected along a climatic gradient. The seed weight and germination dynamics of F1 seeds produced under shared conditions in a common garden experiment were compared with seeds collected in the field (F0). A germination experiment with six constant temperature regimes was performed. Germination dynamics varied considerably between the populations for the F0 seeds. Seeds collected in an area characterized by a semi-arid climate in the eastern part of the gradient showed rapid germination patterns, with time to 50% germination being 1-2 days under a constant temperature regime of 30°C. In contrast, some populations collected from areas with a typical Mediterranean climate, provided an extended germination period for the same temperature regime, with time to 50% germination ranging from 10 to 15 days. Yet in most populations, the germination dynamics of F1 seeds were similar to the rapid increase in germination that characterizes F0 seeds from the eastern populations. Furthermore, the average weight of F1 seeds in eastern populations was lower than that of F0 seeds, while for western populations it was higher, resulting in similar weights among F1 seeds across populations. In this study we found a phenotypic plasticity response to different climatic conditions, showing how species cope with climatic variations and indicating eco-evolutionary mechanisms that enable them to survive extreme environmental conditions and potentially also under novel regimes caused by climate change. These results highlight the need for a regional approach to weed management, taking into account the effects of climate on weed phenology and tailoring control measures accordingly.
