This study compares how Lantana camara, an invasive species, and L. peduncularis, an autochthonous one, cope with drought in Galapagos. Soil surface temperature was the abiotic environmental parameter that best explained variations in photosynthetic stress. Higher soil surface temperatures were recorded in the lowlands and in rain-shadow areas, which were also the driest areas. L. peduncularis, with a shallow root system, behaved as a drought-tolerant species, showing lower relative growth rates, which decreased with leaf water content and higher photosynthetic stress levels in the lowlands and in a northwest rain-shadow area in comparison with higher and wetter locations. Its basal and maximal fluorescences decreased at lower altitudes, reflecting the recorded drops in chlorophyll concentration. In contrast, L. camara with a deep root system behaved as a drought-avoiding species, showing leaf and relative water contents higher than 55% and avoiding permanent damage to its photosynthetic apparatus even in the driest area where it showed very low chlorophyll content. Its relative growth rate decreased more in dry areas in comparison to wetter zones than did that of L. peduncularis, even though it had greater water content. Furthermore, L. camara showed higher water contents, growth rate, and lower photosynthetic stress levels than L. peduncularis in the arid lowlands. Thus, L. peduncularis maintained lower maximum quantum efficiency of photosystem II photochemistry (F v /F m ) than L. camara even at sunrise, due to higher basal fluorescence values with similar maximal fluorescence, which indicated Ó Springer Science+Business Media B.V. 2006 permanent damage to PSII reaction centres. Our results help to explain the success and limitations of L. camara in the invasion of arid and sub-arid environments.

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Interspecific hybridization is an important and common evolutionary mechanism, but field-based evaluations of changes in realized niches and zonation patterns of native and exotic hybrids relative to those of their parental plant species are rare. Would native hybrids forming hybrid zones between their parental species show realized niches similar to that of their parents, whereas would exotic hybrids show larger realized niches than their parents, and alter zonation patterns of native species? To address these questions, we examined key sediment characteristics in plots representing realized niches of native Sarcocornia hybrids, invasive Spartina hybrids and parental species in 14 salt marshes from four estuaries in the Gulf of Cadiz, Southwest Iberian Peninsula. In one representative marsh, the presence of plant taxa relative to intertidal plant zonation was recorded. Results documented that native and fertile hybrids of Sarcocornia had similar realized niche dimensions as their parental species and co-occurred with other plant species, supporting community diversity. However, exotic sterile hybrids of Spartina had realized niche dimensions lower than those of their parental species and occurred in monocultures. The native hybrids played a community structuring role, whereas the exotic Spartina hybrids were a disruptive influence that changed native halophyte zonation pattern and decreased diversity. This negative functional role could intensify if the sterile hybrids evolve and become fertile. Our study suggests the ecological niche dimension concept is an important tool for understanding species roles in ecosystems, incorporating many ideas from the individual to ecosystem levels.

Restoration of salt marshes is critical in the context of climate change and eutrophication of coastal waters because their vegetation and sediments may act as carbon and nitrogen sinks. Our primary objectives were to quantify carbon (C) and nitrogen (N) stocks and sequestration rates in restored marshes dominated by Spartina maritima to provide support for restoration and management strategies that may offset negative aspects of eutrophication and climate change in estuarine ecosystems. Sediment C content was between ca. 13 mg C g(-1)and sediment N content was ca. 1.8 mg N g(-1). The highest C content for S. maritima was recorded in leaves and stems (ca. 420 mg C g(-1)) and the lowest in roots (361 ± 4 mg C g(-1)). S. maritima also concentrated more N in its leaves (31 ± 1 mg N g(-1)) than in other organs. C stock in the restored marshes was 29.6 t C ha(-1); ca. 16 % was stored in S. maritima tissues. N stock was 3.6 t N ha(-1), with 8.3 % stored in S. maritima. Our results showed that the S. maritima restored marshes, 2.5 years after planting, were sequestering atmospheric C and, therefore, provide some mitigation for global warming. Stands are also capturing nitrogen and reducing eutrophication. The concentrations of C and N contents in sediments, and cordgrass relative cover of 62 %, and low below-ground biomass (BGB) suggest restored marshes can sequester more C and N. S. maritima plantations in low marshes replace bare sediments and invasive populations of exotic Spartina densiflora and increase the C and N sequestration capacity of the marsh by increasing biomass production and accumulation.

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