Effects of burial by sand and inundation by fresh- and seawater on seed germination of five tropical beach species

Plants growing on the beach are exposed to substrate mobility, freshwater inundation, and immersion in seawater, which greatly affect germination and species spatial distribution. In greenhouse experiments, we tested whether the most abundant species on the beach at La Mancha (on the Gulf of Mexico) were tolerant to burial and flooding. We buried seeds of Canavalia maritima, Ipomoea pes-caprae, Chamaecrista chamaecristoides, Palafoxia lindenii, and Ambrosia artemisiifolia at different depths. We used fresh- and seawater flooding with two frequencies: permanent and intermittent. The hard-coated seeds of Canavalia, Ipomoea, and Chamaecrista were left scarified and not scarified to test if dormancy was broken by the flooding regimes. Germination decreased as burial depth increased. We calculated a tolerance index for the burial responses, which indicated that Chamaecrista was the most tolerant species, followed by Canavalia and Palafoxia. Flooding inhibited germination, but more so permanent seawater flooding; it was especially lethal for species closest to the ocean such as Canavalia and Ipomoea. After transfer to freshwater, seeds of Chamaecrista, Palafoxia, and Ambrosia germinated. There was no evidence that hard-coat dormancy was broken by flooding. Tolerance to burial seems to be related to the spatial distribution of species but not to germination responses to flooding.