Print PageBackground. Global warming is projected to increase temperatures throughout Europe. Temperature is a critical factor in triggering germination. In seasonal climates temperature is a good indicator of time of germination and dormancy mechanisms are commonly cued to this factor. Changes in temperature may alter germination timing, hence altering population demographic dynamics
Questions. To what extent is the germination of four widespread species in Europe sensitive to temperature? Are populations across a continental gradient equally sensitive? Does the proportion of seeds germinating under simulated fall, winter and spring vary depending on the conditions of temperature (from cold to warm)?
Methods. Seeds of Capsella bursa-pastori (L.) Medik, Daucus carota L., Papaver rhoeas L. and Silene vulgaris (Moench) Garcke were collected from nine populations along a latitudinal gradient through Europe (from Estonia to Spain; 3000 km). Seeds were set to germinate in growth chambers under four initial temperatures simulating fall conditions in south Europe and global warming (17º/7º, 20º/10º, 23º/13º, 26º/16º;12 hs day/night), after which temperatures were reduced to simulate winter (8º/4º, 11º/7º,14º/4º, 17º/13º;12 hs day/night), and later increased again to simulate spring conditions (15º/6º, 18º/9º, 21º/12º, 24º/15º;12 hs day/night). Each simulated season lasted six weeks. Germinated seeds were recorded and removed every 3 or 4 days. Germination mean and speed were analyzed in relation to temperature treatment.
Results/Conclusions
Results. Capsella bursa-pastori was sensitive to the temperature of the germination environment, the highest germination proportions were obtained in the warmest treatment. Daucus carota and Silene vulgaris increased germination speed in the warmer treatment. In all species, final germination and speed differed significantly among populations. Furthermore, Capsella bursa-pastori, Papaver rhoeas and Silene vulgaris responded to the temperature treatments differently depending on the population. Germination was mainly in fall conditions but the proportion of seeds germinating under different seasons exhibited an idiosyncratic response along the latitudinal gradient: some populations germinated only under fall conditions, others under fall and spring, this was independent of the positioning along the gradient.
Conclusions. The species studied showed response to increased temperature. However, germination differences among populations indicate a specific behaviour of the various populations to changes in the germinative thermal regime. This specific response makes it difficult to predict a general response to warming caused by climate change.
