M. Enrique Figueroa

Carry-over of Differential Salt Tolerance in Plants Grown from Dimorphic Seeds of Suaeda splendens

BACKGROUND AND AIMS Halophytic species often show seed dimorphism, where seed morphs produced by a single individual may differ in germination characteristics. Particular morphs are adapted to different windows of opportunity for germination in the seasonally fluctuating and heterogeneous salt-marsh environment. The possibility that plants derived from the two morphs may also differ physiologically has not been investigated previously. METHODS Experiments were designed to investigate the germination characteristics of black and brown seed morphs of Suaeda splendens, an annual, C(4) shrub of non-tidal, saline steppes. The resulting seedlings were transferred to hydroponic culture to investigate their growth and photosynthetic (PSII photochemistry and gas exchange) responses to salinity. KEY RESULTS Black seeds germinated at low salinity but were particularly sensitive to increasing salt concentrations, and strongly inhibited by light. Brown seeds were unaffected by light, able to germinate at higher salinities and generally germinated more rapidly. Ungerminated black seeds maintained viability for longer than brown ones, particularly at high salinity. Seedlings derived from both seed morphs grew well at high salinity (400 mol m(-3) NaCl). However, seedlings derived from brown seeds performed poorly at low salinity, as reflected in relative growth rate, numbers of branches produced, F(v)/F(m) and net rate of CO(2) assimilation. CONCLUSIONS The seeds most likely to germinate at high salinity in the Mediterranean summer (brown ones) retain a requirement for higher salinity as seedlings that might be of adaptive value. On the other hand, black seeds, which are likely to delay germination until lower salinity prevails, produce seedlings that are less sensitive to salinity. It is not clear why performance at low salinity, later in the life cycle, might have been sacrificed by the brown seeds, to achieve higher fitness at the germination stage under high salinity. Analyses of adaptive syndromes associated with seed dimorphism may need to take account of differences over the entire life cycle, rather than just at the germination stage.

Synergic effect of salinity and CO2 enrichment on growth and photosynthetic responses of the invasive cordgrass Spartina densiflora

Spartina densiflora is a C4 halophytic species that has proved to have a high invasive potential which derives from its clonal growth and its physiological plasticity to environmental factors, such as salinity. A greenhouse experiment was designed to investigate the synergic effect of 380 and 700 ppm CO2 at 0, 171, and 510 mM NaCl on the growth and the photosynthetic apparatus of S. densiflora by measuring chlorophyll fluorescence parameters, gas exchange and photosynthetic pigment concentrations. PEPC activity and total ash, sodium, potassium, calcium, magnesium, and zinc concentrations were determined, as well as the C/N ratio. Elevated CO2 stimulated growth of S. densiflora at 0 and 171 mM NaCl external salinity after 90 d of treatment. This growth enhancement was associated with a greater leaf area and improved leaf water relations rather than with variations in net photosynthetic rate (A). Despite the fact that stomatal conductance decreased in response to 700 ppm CO2 after 30 d of treatment, A was not affected. This response of A to elevated CO2 concentration might be explained by an enhanced PEPC carboxylation capacity. On the whole, plant nutrient concentrations declined under elevated CO2, which can be ascribed to the dilution effect caused by an increase in biomass and the higher water content found at 700 ppm CO2. Finally, CO2 and salinity had a marked overall effect on the photochemical (PSII) apparatus and the synthesis of photosynthetic pigments.

Effects of Salinity on Germination and Seedling Establishment of Endangered Limonium emarginatum (Willd.) O. Kuntze

Abstract The germination and subsequent seedling establishment of Limonium emarginatum, an endangered and endemic halophyte of the Strait of Gibraltar, was studied under exposure to different NaCl concentrations (0, 2, 4, and 6%) in a laboratory experiment. We assessed final germination percentage, number of days to first and final germination, mean time to germinate (MTG), as well as seed viability and seedling survival. Increasing salinity delayed the beginning and ending of germination and reduced final germination percentage, inhibiting germination completely above 2% salinity. L. emarginatum exhibited the greatest germination in fresh water. When seeds were removed from all saline solutions, between 60% and 70% of final germination was recorded, although at hypersalinity, germination viability diminished. Salinity pretreatments had a stimulatory effect on germination since germination speed was higher for the recovery experiment than for the seed germination experiment. Transition between germination and seedling establishment was a critical phase, given that less than 50% of seedlings of L. emarginatum survived in distilled water and 5% survived at 2% salinity.

CLONAL GROWTH AND TILLER DEMOGRAPHY OF THE INVADER CORDGRASS SPARTINA DENSIFLORA BRONGN. AT TWO CONTRASTING HABITATS IN SW EUROPEAN SALT MARSHES

Salt marshes offer a valuable opportunity to study the effects of environment on the clonal growth of species able to live throughout a wide vertical range on the tidal frame. Spartina densiflora is a species native to South America that is invading marshes in SW Europe, NW Africa, and SW North America, where its populations are found from low to high topographic elevations, altering the composition of plant communities. The aim of this study was to increase our knowledge regarding the competitive ability of S. densiflora, analyzing its clonal growth and its ramet demography during 25 months in two expanding populations at a low and a high marsh. Four clonal characteristics were recorded in both populations: (1) dense occupation of available space inside tussocks; (2) lack of a dormant period and high tiller production rates and growth; (3) evidence of physiological integration between ramets; and (4) high rates of sexual reproduction. Furthermore, S. densiflora developed different strategies of clonal growth in contrasting habitats. Tussocks in the low marsh had lower tiller longevity and higher tiller density, natality, and mortality rates, showing faster ramet turnover than in the high marsh. These clonal growth traits would facilitate S. densiflora persistence under the effects of catastrophic events. Spartina densiflora clonal growth traits indicate strong adaptability to different environmental conditions and strong competitive ability, since its tiller dynamics enable it to invade occupied space, and it effectively colonizes new safe-sites by sexual reproduction. These observations help us to understand how this invader has become the most abundant plant in many estuaries of the SW Iberian Peninsula.

Phenotypic plasticity of invasive Spartina densiflora (Poaceae) along a broad latitudinal gradient on the Pacific Coast of North America

PREMISE OF THE STUDY Phenotypic acclimation of individual plants and genetic differentiation by natural selection within invasive populations are two potential mechanisms that may confer fitness advantages and allow plants to cope with environmental variation. The invasion of Spartina densiflora across a wide latitudinal gradient from California (USA) to British Columbia (Canada) provides a natural model system to study the potential mechanisms underlying the response of invasive populations to substantial variation in climate and other environmental variables. METHODS We examined morphological and physiological leaf traits of Spartina densiflora plants in populations from invaded estuarine sites across broad latitudinal and climate gradients along the Pacific west coast of North America and in favorable conditions in a common garden experiment. KEY RESULTS Our results show that key foliar traits varied widely among populations. Most foliar traits measured in the field were lower than would be expected under ideal growing conditions. Photosynthetic pigment concentrations at higher latitudes were lower than those observed at lower latitudes. Greater leaf rolling, reduced leaf lengths, and lower chlorophyll and higher carbon concentrations were observed with anoxic sediments. Lower chlorophyll to carotenoids ratios and reduced nitrogen concentrations were correlated with sediment salinity. Our results suggest that the variations of foliar traits recorded in the field are a plastic phenotypic response that was not sustained under common garden conditions. CONCLUSIONS SPARTINA DENSIFLORA shows wide differences in its foliar traits in response to environmental heterogeneity in salt marshes, which appears to be the result of phenotypic plasticity rather than genetic differentiation.

Heavy metals and trace element concentrations in intertidal soils of four estuaries of SW Iberian Peninsula

Soils from four estuaries of SW Iberian Peninsula, affected by anthropogenic influence (urban, industrial and agricultural activities), were analyzed for the occurrence of a variety of metals and trace elements including Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S and Zn. The soils presented very high levels of salinity (high concentrations of Na, K and Mg), organic matter and, consequently, of C and N concentrations. In contrast, very low values of CaCO3, Ca and P were found. In addition, it should be highlighted that in certain localities (Piedras 1 and 2 and Guadiana in Huelva, Spain, and Ria Formosa, Faro, Portugal) the concentrations of Pb, S and Zn were extremely high, reaching levels of pollution.

Exploring molecular variation in the cosmopolitan Caprella penantis (Crustacea: Amphipoda): results from RAPD analysis

Eight populations of Caprella penantis , three of Caprella dilatata and two of Caprella andreae , collected from different sites all over the world, were selected for genetic study. Thirteen primers were tested, and the phenogram, based on the similarity coefficient of Nei & Li and the UPGMA method, separated clearly C. dilatata and C. andreae from the populations of C. penantis , supporting the validity of these three species, traditionally considered altogether under the old ‘acutifrons’ complex. Populations of C. penantis (including, at least, forms simulatrix, testudo and lusitanica ) from Spain, Portugal, Morocco, Japan and Brazil were clustered together in the RAPD analysis, indicating that, probably, all the specimens of C. penantis could belong to the same species, in spite of morphological variations in the pleura, gills, robustness and presence/absence of proximal projection in adult male gnathopod 2 propodus. The only population which showed genetic differentiation within the C. penantis complex was the form gibbosa from Coquimbo, Chile. Future analysis based on different molecular approaches (mtDNA, 18S rRNA, ISSR) and additional material from other world areas, should be conducted to confirm these results.