Ecological significance of seed germination characteristics in flood-meadow species

In climate chamber and outdoor experiments we analysed germination traits of 42 vascular plant species typical of flood-meadows of the alliance Cnidion. In Central Europe such flood-meadows and their highly endangered character species are confined to large lowland river corridors with a dry and warm climate. Due to the prevailing ecological conditions, particularly the extremely high variability in soil moisture potential, it was hypothesised that flood-meadow species exhibit specific strategies in terms of germination phenology, temperature requirements and primary dormancy to avoid constraints on seedling recruitment imposed by flooding, drought and competition from established vegetation. Furthermore, we expected that germination characteristics could be a key for the causal understanding of range size, confinement to large river corridors, recent rarification processes, seed bank persistence and establishment success in restoration projects. PCA ordination of germination traits reflected a continuous gradient of increasing primary dormancy levels ranging from species with a high capacity for fast and almost complete germination over a wide range of temperatures to those with high and narrow temperature requirements and/or a delayed and asynchronous emergence. Many of the studied species germinated only at relatively high temperature in the year of shedding, but the primary conditional dormancy disappeared in most cases after a period of cold wet stratification. Requirements for chilling and/or high germination temperature were revealed to be the most common strategies for avoidance of harmful autumn and winter germination. The majority of the studied species tends to exploit particularly favourable regeneration niches in early spring. Surprisingly, many species with large long-term persistent soil seed banks exhibited relatively low dormancy levels in light; this was correlated with small seed size and a consequent higher probability of burial. We found no relationship between germination characteristics and river corridor confinement or Central European range size. However, there was a significant trend in endangered species towards higher temperature requirements and delayed, asynchronous germination. This is presumably disadvantageous under the environmental conditions of subcontinental flood-meadows.