Aproximación ecológica al estado de conservación de las poblaciones de Limonium emarginatum, un endemismo del Estrecho de Gibraltar

Limonium emarginatum es una especie endómica de los acantilados del estrecho de Gibraltar. El objetivo de este trabajo fue analizar qué factores condicionan la distribución de L. emarginatum, estudiando las especies vegetales acompañantes, así como diferentes variables del medio físico en seis poblaciones. L. emarginatum apareció principalmente en zonas rocosas de fuerte pendiente cercanas al mar acompañaado por Silene obtusifolia, Frankenia hirsuta y Spergularia fimbriata. Su cobertura disminuyó acusadamente en zonas más alejadas de la costa, donde dominaron especies como Elymus farctus, Sporobolus pungens y la invasora sudafricana Carpobrotus edulis. En algunas poblaciones la presencia de Carpobrotus edulis constituye un problema importante para la supervivencia de L. emarginatum. Estas especies más competidoras quedarían excluidas de las zonas bajas debido a los altos niveles de estrés ambiental. Nuestros resultados parecen reflejar una fuerte heterogeneidad ambiental, que unida a posibles problemas en la dispersión, auspiciaría la presencia de un número relativamente elevado de taxones de distribución restringida en puntos geográficamente cercanos. En general, el estado de conservación de las poblaciones fue muy variado, estando la presencia del endemismo gaditano restringida por exclusión competitiva a zonas rocosas cercanas al mar y de fuerte pendiente

Seedling Emergence from Seed Banks in Ludwigia hexapetala-Invaded Wetlands: Implications for Restoration

Soil seed banks play a critical role in the maintenance of wetland plant communities and contribute to revegetation following disturbances. Analysis of the seed bank can therefore inform restoration planning and management. Emergence from seed banks may vary in response to hydrologic conditions and sediment disturbances. To assess the community-level impact of exotic Ludwigia hexapetala on soil seed banks, we compared differences in species composition of standing vegetation among invaded and non-invaded wetlands and the degree of similarity between vegetation and soil seed banks in northern California. To determine potential seed bank recruitment of L. hexapetala and associated plant species, we conducted a seedling emergence assay in response to inundation regime (drawdown vs. flooded) and sediment depth (surface vs. buried). Plant species richness, evenness, and Shannon’s H’ diversity were substantially lower in standing vegetation at L. hexapetala invaded sites as compared to non-invaded sites. Over 12 months, 69 plant taxa germinated from the seed banks, including L. hexapetala and several other exotic taxa. Seedling density varied among sites, being the highest (10,500 seedlings m−2) in surface sediments from non-invaded sites subjected to drawdown treatments. These results signal the need for invasive plant management strategies to deplete undesirable seed banks for restoration success

Transgressivity in Key Functional Traits Rather Than Phenotypic Plasticity Promotes Stress Tolerance in A Hybrid Cordgrass

Hybridization might promote offspring fitness via a greater tolerance to environmental stressors due to heterosis and higher levels of phenotypic plasticity. Thus, analyzing the phenotypic expression of hybrids provides an opportunity to elucidate further plant responses to environmental stress. In the case of coastal salt marshes, sea level rise subjects hybrids, and their parents, to longer tidal submergence and higher salinity. We analyzed the phenotypic expression patterns in the hybrid Spartina densiflora x foliosa relative to its parental species, native S. foliosa, and invasive S. densiflora, from the San Francisco Estuary when exposed to contrasting salinities and inundations in a mesocosm experiment. 37% of the recorded traits displayed no variability among parents and hybrids, 3% showed an additive inheritance, 37% showed mid-parent heterosis, 18% showed best-parent heterosis, and 5% presented worst-parent heterosis. Transgressivity, rather than phenotypic plasticity, in key functional traits of the hybrid, such as tiller height, conveyed greater stress tolerance to the hybrid when compared to the tolerance of its parents. As parental trait variability increased, phenotypic transgressivity of the hybrid increased and it was more important in response to inundation than salinity. Increases in salinity and inundation associated with sea level rise will amplify the superiority of the hybrid over its parental species. These results provide evidence of transgressive traits as an underlying source of adaptive variation that can facilitate plant invasions. The adaptive evolutionary process of hybridization is thought to support an increased invasiveness of plant species and their rapid evolution

Cuantificación de la erosión en los canales mareales de las maarismas del Odiel (Huelva, SO de España)

Este estudio se llevó a cabo en las Marismas del Odiel (Huelva, SO España). En él se cuantifican la acreción y erosión de sedimentos en taludes desarrollados en canales intermareales y en las planicies intermareales subayacentes. Se registró una erosión generalizada de los taludes, la cual se vería potenciada por actuaciones antrópicas como el tráfico naval y la alteración de la hidrodinámica del estuario por la construcción de diques. Las pérdidas de marismas en la Reserva Integral de Isla de Enmedio se estimaron en 3000 m2/ año, lo que supone una movilización de 1850 m3 de sedimentos. Esta fuerte erosión podría tener una gran influencia en la conservación de este espacio natural protegido, además de acelerar la colmatación de los canales del estuario. La vegetación, entre la que destacaron las praderas de Zostera noltii, disminuyó la erosión, potenciando la acreción. La dinámica vertical de sedimentos en las planicies intermareales mostró un patrón estacional con una relación clara entre la erosión y la distribución de las lluvias. Se discuten medidas de control de la erosión y rehabilitación de las zonas afectadas.This study was carried out in Odiel Saltmarshes (Huelva, SWSpain). Erosion and accretion in slopes and intertidal mud flats were measured. Our results point out a general retrogression of slopes. Its intensity would depend on anthropic actions as boats traffic and alteration of estuary circulation by dykes construction. In the Integral Reserve of Enmedio Island, horizontal losses by erosion in slopes reached 3000 m2/year, which would imply the mobilization of 1850 m3 of sediments. This strong erosion could cause important changes in this protected area and to selt-up of the navigable channels of the estuary. Vegetation, as prairie of eelgrass Zostera noltii, decreased erosion and increased acretion rates. Sediment vertical dynamic in intertidal mud flats showed a seasonal pattern with a direct relation between erosion and rainfall distribution. Erosion control and rehabilitation in eroded areas are discussed

Biomass and clonal architecture of the cordgrass Spartina patens (Poaceae) as an invasive species in two contrasted coastal habitats on the Atlantic coast of the Iberian Peninsula

Background and aims – The spread of invasive exotic species is one of the most important threats for salt marshes and cordgrasses (genus Spartina) are among the most invasive halophytes. Recent analyses have revealed low levels of genetic diversity within the European cordgrass Spartina patens, clarifying that it was introduced from a narrow genetic pool of plants from North America. As biomass and intratussock structure are key functional traits in the ecological behaviour of cordgrasses, our aim was to document this here for the first time in Spartina patens in Europe. Methods – This work analyses above- and below-ground biomass and intratussock structure for two Spartina patens populations in Southern Spain in the two main invaded habitats in Europe, coastal dunes and brackish marshes. Key results – Spartina patens showed higher above-ground biomass and higher above: below-ground biomass ratio in the brackish marsh than on the coastal dunes due to higher live shoot densities with similar shoot heights. Sexual reproduction of Spartina patens was very limited in both studied populations since only a few inflorescences were recorded in just one tussock in the marsh. Conclusions – Our results for introduced Spartina patens in Spain are compared with those recorded for cohabiting cordgrasses, the native European Spartina maritima and the invasive Spartina densiflora, as well as with Spartina patens in North American marshes. Spartina patens appears as a species with moderate invasive potential in European coastal marshes and dunes since it shows very low sexual reproduction but a high phenotypic plasticity, which would support its invasive capacity. Eradication efforts are most cost effective in the early stage of infestation, when population sizes are still relatively small, and should thus be a focus of the control efforts of S. patens in the Southwest Iberian Peninsula as well as in other European areas, where this cordgrass is still not very abundant

El empleo de técnicas de control y erradicación en la lucha contra especies invasoras: conveniencia de la herbivoría como método de bio-control de la invasión de Spartina densiflora brongn. en el Campo de Gibraltar

Spartina densiflora es una gramínea procedente de Sudamérica que está invadiendo numerosas marismas mareales en el golfo de Cádiz provocando problemas muy graves para la conservación de estos ecosistemas, como la pérdida de biodiversidad. En el Campo de Gibraltar Spartina densiflora se localiza en las desembocaduras de los ríos Vega y Jara y en el estuario del río Palmones. Conocer el estado de la invasión en estas zonas es de especial relevancia a la hora de optar entre diferentes técnicas de erradicación o control. Mientras en el río Palmones sería factible la eliminación mecánica de los clones de Spartina densiflora, en el caso de los estuarios de los ríos Vega y Jara el empleo de la ganadería como medida de bio-control parece la estrategia más aconsejable. No obstante, la amplia gama de efectos que la presión de la herbivoría provoca sobre las comunidades vegetales y, en concreto, sobre la evolución de especies invasoras hace necesario llevar a cabo estudios detallados sobre la utilidad de la ganadería como herramienta de gestión en materia de especies invasoras

Morphological and physiological responses of Galapagos endemic tree Croton scouleri to site conditions varying through its altitudinal range

: Galapagos is a natural laboratory offering a great opportunity to study plants functional traits. This study characterises morphological and ecophysiological responses of Croton scouleri, an endemic tree that habits from humid and upper elevations to semiarid lowlands, throughout an altitudinal gradient and in a manipulative experiment. Croton scouleri trees were gradually smaller with less total leaf area due to a gradual reduction in mean leaf size, and they folded their leaves at lower elevations. These results were also recorded after cutting every deep root. Two physiological traits that allowed Croton scouleri to avoid damages to the photosynthetic apparatus were detected between 30 and 150 m a.s.l. Lower variable fluorescence (Fv) and basal fluorescence (F0) keeping constant maximum photochemical efficiency of PSII (Fv/Fm) denoted a drop in chlorophyll concentration. Concomitantly, the recorded increase in the Quantum efficiency of PSII ( PSII) with similar Fv/Fm means that Croton scouleri could be using cyclic electron transport as photoprotective mechanism. On the other hand, a deep root system to reach the water table allowed Croton scouleri to behave as a drought-avoider, which was reflected in: (1) unvarying water status Leaf Water Content and Relative Water Content were always higher than 69 and 58%, respectively; (2) stable and low photoinhibition levels; and (3) unvarying leaf area index. However, Croton scouleri was not able to avoid drought at altitudes lower 30 m a.s.l. where similar responses to those recorded after root cutting were recorded.Junta de Andalucía AI60/0

Phenotypic plasticity of polyploid plant species promotes transgressive behaviour in their hybrids

Hybridization is a frequent process that leads to relevant evolutionary consequences, but there is a lack of studies regarding the relationships of the variability of the response of parental plant species to environmental gradients and the responses of their hybrids at a phenotypic level. We designed an experiment in which we exposed two reciprocal cordgrass hybrids, Spartina maritima × densiflora and S. densiflora × maritima, and their parental species to four salinity concentrations for 30 days. The main objectives were to compare the performance of the hybrids with that of their parents, to distinguish the phenotypic inheritance operating in the hybrids and to analyse the relationships between the variability in the responses of the parents and the responses of their hybrids to salinity. We characterized the responses and the degree of variability for 37 foliar traits. Both hybrids presented greater salinity tolerance than their parents, showing their highest percentage of transgressive traits at both extremes of the salinity gradient. When the parental plants themselves showed a more plastic response for a given trait, there was a greater chance that their hybrid developed a transgressive behaviour for this trait. This finding supports a new focus to be applied for the artificial development of vigorous hybrid crops

Effects of competition from the invasive Cordgrass Spartina densiflora on Native Atriplex portulacoides

Invasion by the South American cordgrass Spartina densiflora Brongn. in European salt marshes is causing concern about potential impacts to native plant communities., S. densiflora colonization of mid-marsh habitats may be slowed by native Atriplex portulacoides L., but the mechanism behind this negative interaction is not known. The aim of this work was to study the establishment and growth response of S. densiflora seedlings grow-ing in a competitive environment with mature A. portulacoides plants in controlled greenhouse conditions. With this aim we measured establishment, growth, foliar nutrients, and photosynthetic pigments of S. densiflora plants grown with and without A. portulacoides. Results showed that S. densiflora seedlings readily established in mature stands of A. portulacoides. Every Spartina clump growing with Atriplex survived, producing fewer tillers with simi-lar heights than when growing without competition, which was reflected on lower above-ground biomass. These results indicated that S. densiflora was affected at the above-ground level by the interspecific competition with Atriplex, but the invasive cordgrass was able to keep similar below-ground bio-mass with and without competition, resulting in a decrease of below-ground biomass of Atriplex when competing with Spartina. Our results in green-house controlled conditions were in agreement with our field observations where S. densiflora plants have been observed growing within A. portu-lacoides monospecific communities

Differential Effects of Increasing Salinity on Germination and Seedling Growth of Native and Exotic Invasive Cordgrasses

Soil salinity is a key environmental factor influencing germination and seedling establishment in salt marshes. Global warming and sea level rise are changing estuarine salinity, and may modify the colonization ability of halophytes. We evaluated the effects of increasing salinity on germination and seedling growth of native Spartina maritima and invasive S. densiflora from wetlands of the Odiel-Tinto Estuary. Responses were assessed following salinity exposure from fresh water to hypersaline conditions and germination recovery of non-germinated seeds when transferred to fresh water. The germination of both species was inhibited and delayed at high salinities, while pre-exposure to salinity accelerated the speed of germination in recovery assays compared to non-pre-exposed seeds. S. densiflora was more tolerant of salinity at germination than S. maritima. S. densiflora was able to germinate at hypersalinity and its germination percentage decreased at higher salinities compared to S. maritima. In contrast, S. maritima showed higher salinity tolerance in relation to seedling growth. Contrasting results were observed with differences in the tidal elevation of populations. Our results suggest S. maritima is a specialist species with respect to salinity, while S. densiflora is a generalist capable of germination of growth under suboptimal conditions. Invasive S. densiflora has greater capacity than native S. maritima to establish from seed with continued climate change and sea level rise.Ministerio de Educación, Cultura y Deporte (FPU14/06556