Aspectos reproductivos de la flora de dunas y marismas de las costas de Huelva (SO España)

Resumen

Tidal salt marshes represent 5% of the world's wetlands, being located on protected coasts where the influence of the waves is so low that it allows the establishment of halophilic vegetation. They are stressful environments dominated by spatio-temporal gradients that depend on the elevation of the substrate with respect to the intertidal frame. This thesis focuses the first of its studies on the effects of salinity on germination, a decisive factor for the establishment of vegetation in the salt marshes. It studied the response to six NaCl concentrations (0.0; 0.1; 0.2; 0.3; 0.6 and 0.9 M) of 8 common species of the chenopodiaceae family that inhabit the salt marshes of the Gulf of Cadiz: Sarcocornia perennis, Atriplex portulacoides, Sarcocornia fruticosa, Salicornia ramosissima, Arthrocnemum macrostachyum, Suaeda vera, Salsola vermiculata and Sarcocornia alpini. Germination was recorded for 30 days in each salinity and, subsequently, germination in distilled water was observed in the non-germinated seeds (recovery test). The results show that high salinities inhibit germination, tending to accelerate it in recovery trials. 4 germination syndromes were established: 1) high germination at lowmedium salinities and reduced after exposure to high salinity; 2) no germination in hypersalinity and high recovery in fresh water; 3) accelerated germination after exposure to salinity; and 4) germination over a wide range of salinity. Overall, germination of high salt marsh species was characterized by marked responses to salinity changes, while that of low saltmarsh species showed low sensitivity to salinity fluctuations. The second paper studies the importance for salt marsh vegetation of the establishment of a seed bank, a key aspect for resilience, secondary succession, and ecosystem restoration. It was revealed that 12 of the18 taxa studied form transient seed banks, and only 6 taxa established persistent seed banks. The strategies of dispersion of the propagules throughout the intertidal gradient were also analyzed, defining 3 strategies: 1) dispersion at short distance, 2) dispersion at medium-long distance and 3) mixture of both behaviors. The last two studies focus on the annual species Salicornia ramosissima (Amaranthaceae) that is gaining socio-economic importance due to its traditional uses as food and non-traditional ones such as its use in biofilters, among others. Therefore, it is necessary to design strategies for the correct use of wild populations and good management practices. To do this, the seed bank was studied, both aerial and soil, as well as the dynamics of these in four wild populations of S. ramosissima. The results show that seed production depended mainly on the density of plants rather than on the number of seeds produced by each individual plant. In addition, most of the seed production was exported outside the populations studied, accumulating a maximum of 20% of the seeds in the initial banks, establishing a permanent seed bank in two of the four populations studied. Finally, the environmental matrix and population dynamics of four populations of S. ramosissima were studied at two different elevations. In the high populations, densities between 628 and 6,288 plants/m2 were recorded, in contrast to the depressed areas in which we obtained densities from the soil seed bank and plants five times higher. Density-dependent mortality was also recorded for the densest population. Our results offer interesting information for the sustainable exploitation of the natural populations of S. ramosissima.