Effect of temperature on the installation and growth of annuals in Mediterranean temporary marshes

The abundance of annual plants in temporary marshes is subjected to strong fluctuations through time. Such fluctuations could be linked with the variability of the Mediterranean climate. We studied experimentally the relationships between those fluctuations of abundance and the water temperature. The establishment and growth pattern of the species were studied in three temperate ranges. Each species has its own germination pattern, which varies with the temperature. The speed of seedling emergence changes with the temperature for all species. The germination rate is modified significantly only for charophytes, with a strong decrease under cold conditions. The size of the diaspore bank explains a large part of the germination dynamics for Chara sp. and Zannichellia spp. At the end of the establishment stage, the cover is maximum under warm conditions and Callitriche truncata and Zannichellia spp. have the largest cover values. At the end of the growth period, Ranunculus boudotii generally dominates the community in terms of biomass, whereas C. truncata is dominated. Species biomass varies with the temperature during the establishment or (and) the growth stage, except for Zannichellia spp. There is no obvious ''preemption'' effect: the contrasted life history strategies among species allow dominance relationship modifications during the life cycle.