Germination of Avicennia schaueriana and Laguncularia racemosa from two physiographic types of mangrove forest

In order to evaluate intra-specific differences related to the source of propagules this study conducted biometric and germination analyses considering two physiograpic types of mangrove forests: fringe and shrub-basin. These forests represent the extremities of a marked gradient of tidal flooding frequency, going from river to salt flat. Germination tests were performed in control conditions (distilled water and without addition of water) and in solutions of NaCl or polyethylene glycol 6000 which are equivalent to water potentials (Ψ) of −0.4, −0.8, −1.6 and −2.4 MPa. The parameters analyzed were germinability (G; %) and mean germination time index (t, days), which report viability and vigour of propagules, respectively. Results revealed significant intra-specific differences: smaller propagules (differences were about 1.7 and 1.2 mm in length for Avicennia schaueriana and Laguncularia racemosa, respectively) with lower viability (differences were from 16.2 to 43.2% in G for both species) from shrub-basin in relation to fringe forest and stronger vigour (reductions in t were from 1 to 3 days) of the L. racemosa propagules from the shrubs. We also noted that water potentials promoted by NaCl were more severe for A. schaueriana than for L. racemosa and that the opposite effect occurred with PEG.