Hardseededness in annual clovers: variation within populations and subsequent shifts due to environmental changes

The first experiment investigated the possibility of variation in seed softening patterns from progeny of individual clover plants from the same population. Patterns of seed softening were attained by exposing seeds on the soil surface over a single summer-autumn period. Logistic curves were fitted to these softening patterns. Comparison of parameters of logistic curves demonstrated that there was within-population variation for hardseededness at maturity, amount of hard seeds entering the seedbank after 6 months on the soil surface, and the time at which seeds softened. The existence of such variation within populations is required for natural selection in response to environmental changes. The second experiment compared hardseededness in populations of 2 clovers from different grazing and phosphate fertiliser treatments from a long-running grassland management trial in Syria. Differences in hardseedness (after 6 months exposure on the soil surface) between treatments demonstrated the importance of dormancy to the reproductive ecology of these clovers.