Nitrate modulates the physiological tolerance responses of the halophytic species Sarcocornia fruticosa to copper excess.

Coexistence impact of pollutants of different nature on halophytes tolerance to metal excess has not been thoroughly examined, and plant functional responses described so far do not follow a clear pattern. Using the Cu-tolerant halophyte Sarcocornia fruticosa as a model species, we conducted a greenhouse experiment to evaluate the impact of two concentration of copper (0 and 12 mM CuSO4) in combination with three nitrate levels (2, 14 and 50 mM KNO3) on plant growth, photosynthetic apparatus performance and ROS-scavenging enzymes system. The results revealed that S. fruticosa was able to grow adequately even when exposed to high concentrations of copper and nitrate. This response was linked to the plant capacity to uptake and retain a large amount of copper in its roots (up to 1500 mg kg-1 Cu), preventing its transport to aerial parts. This control of translocation was further magnified with nitrate concentration increment. Likewise, although Cu excess impaired S. fruticosa carbon assimilation capacity, the plant was able to downregulate its light-harvesting complexes function, as indicated its lowers ETR values, especially at 12 mM Cu + 50 mM NO3. This downregulation would contribute to avoid excess energy absorption and transformation. In addition, this strategy of avoiding excess energy was accompanied by the upregulation of all ROS-scavenging enzymes, a response that was further enhanced by the increase in nitrate concentration. Therefore, we conclude that the coexistence of nitrate would favor S. fruticosa tolerance to copper excess, and this effect is mediated by the combined activation of several tolerance mechanisms.

Disentangling elevation, annual flooding regime and salinity as hydrochemical determinants of halophyte distribution in non-tidal saltmarsh.

BACKGROUND AND AIMS: Hydrological disconnection, especially in a Mediterranean climate, creates coastal saltmarshes with an annual cycle of flooding that are unlike tidally inundated systems. Winter rainfall produces long, continuous hydroperiods, alternating with continuous exposure caused by evaporation in warm, rain-free summers. We aimed to distinguish the effects of elevation, hydroperiod and salinity on annual and perennial halophytes in such a system. METHODS: We recorded vegetation and sediment salinity in permanent quadrats on a marsh in the Doñana National Park, Spain, over seven consecutive years with widely differing rainfall. Elevation was determined from LIDAR data and the duration of the annual hydroperiod from satellite imagery. The independent effects of collaterally varying elevation, hydroperiod and salinity on species distribution were examined using generalized linear models and hierarchical partitioning. KEY RESULTS: Both hydroperiod and salinity were inversely related to elevation but interannual fluctuations in rainfall facilitated discrimination of independent effects of the three collaterally varying factors on halophyte distribution. Perennial distribution was strongly structured by elevation, whereas many annual species were more sensitive to hydroperiod. The independent effects of salinity varied according to individual species' salt tolerance from positive to negative. Thus life-history and, in the case of annuals, phenology were important in determining the relative impact of elevation and hydroperiod. CONCLUSIONS: The consequences of elevation for halophyte distribution in seasonally flooded saltmarshes are fundamentally different from those in tidal marshes, because protracted and frequent flooding regimes require different adaptations, and because of the unpredictability of flooding from year to year. These differences could explain greater species diversity in non-tidal marshes and the absence of key saltmarsh species prominent in tidal marshes. The vegetation of non-tidal marshes will be particularly susceptible to the more extreme annual cycles of temperature and rainfall predicted for Mediterranean climates.

Radionuclides transfer into halophytes growing in tidal salt marshes from the Southwest of Spain.

Estuaries are sinks of materials and substances which are released directly into them or transported from rivers that drain the basin. It is usual to find high organic matter loads and fine particles in the sediments. We analyzed radionuclide concentrations ((210)Po, (230)Th, (232)Th, (234)U, (238)U, (226)Ra, (228)Th, (228)Ra, (40)K) in sediments and three different organs (roots, stems and leaves) of three species of halophytes plants (Spartina maritima, Spartina densiflora and Sarcocornia perennis). The study was carried out in two tidal salt marshes, one polluted by U-series radionuclides and another nearby that was unpolluted and was used as a control (or reference) area. The Tinto River salt marsh shows high levels of U-series radionuclides coming from mining and industrial discharges. On the contrary, the unperturbed Piedras River salt marsh is located about 25 km from the Tinto marsh, and shows little presence of contaminants and radionuclides. The results of this work have shown that natural radionuclide concentrations (specially the U-isotopes) in the Tinto salt marsh sediments are one order of magnitude higher than those in the Piedras marsh. These radionuclide enhancements are reflected in the different organs of the plants, which have similar concentration increases as the sediments where they have grown. Finally, the transfer factor (TF) of the most polluted radionuclides (U-isotopes and (210)Po) in the Tinto area are one order of magnitude higher than in the Piedras area, indicating that the fraction of each radionuclide in the sediment originating from the pollution is more available for the plants than the indigenous fraction. This means that the plants of the salt marshes are unhelpful as bioindicators or for the phytoremediation of radionuclides.