Permanently or seasonally flooded wetlands are hotspots for plant diversity. Their community composition usually depends strongly on hydrological conditions, suggesting that hydrology drives community assembly. However, the mechanisms underlying this effect are still not fully understood, and they could arise either through hydrological effects on reproduction, growth or mortality of plants. Here, we concentrate on the effect of hydrology on seed germination, also known as the recruitment niche. We investigated seed germination in sediments from eight localities in southern Germany under four permanent and two temporal flooded treatments and tested for the association of species' hydrological niches with their functional traits (type of dormancy, alternating temperature and oxygen requirements for germination). Our results show that hydrological conditions significantly affected species-specific germination. Interspecific variation in germination responses could be partly explained by seed physiological traits: non-dormant species were more likely to germinate in non-flooded hydrological treatments and species with alternating temperature and oxygen requirements exhibited higher germination in dry and wet treatments. The longer flooded conditions persisted, the more negatively they affected the germination of these species. Overall, we conclude that hydrological conditions have trait-mediated species-specific effects on seed germination, and that these effects likely contribute to the final community composition.
Mašková et al. (Wed,) studied this question.