Abstract
Waterlogging and submergence are the major constraints to which wetland plants are subjected, with inevitable impacts on their physiology and productivity. Global warming and climate change, as driving forces of sea level rise, tend to increase such submersion periods and also modify the carbonate chemistry of the water column due to the increased concentration of CO2 in the atmosphere. In the present work, the underwater O2 fluxes in the leaves of two abundant Mediterranean halophytes were evaluated at different levels of dissolved CO2. Photosynthetic enhancement due to increased dissolved CO2 was confirmed for both Halimione portulacoides and Spartina maritima, probably due to high tissue porosity, formation of leaf gas films and reduction of the oxygenase activity of Rubisco. Enhancement of the photosynthetic rates in H. portulacoides and S. maritima was concomitant with an increase in energy trapping and transfer, mostly due to enhancement of the carboxylation reaction of Rubisco, leading to a reduction of the energy costs for carbon fixation. Transposing these findings to the ecosystem, and assuming increased dissolved CO2 concentration scenarios, the halophyte community displays a new ecosystem function, increasing the water column oxygenation and thus reinforcing their role as principal primary producers of the estuarine system.
Highlights
Wetlands are among the most productive ecosystems of the planet, retaining about one-half to one-third of the carbon fixed and providing important ecosystem services to the estuarine system, namely nutrient regeneration, primary production and shoreline stabilization as well as a habitat for wildlife (Cacador et al 2009)
Taking into account the present projections made by the Intergovernmental Panel for Climate Change (IPCC), it is expected that the increased levels of atmospheric CO2 will lead to an inevitable increase in the dissolved CO2 in water bodies (IPCC 2002), in this way altering the availability of CO2 underwater
We report the O2 dynamics in both light-exposed and dark-incubated leaves of C3 H. portulacoides and C4 S. maritima under different dissolved CO2 concentrations
Summary
Wetlands are among the most productive ecosystems of the planet, retaining about one-half to one-third of the carbon fixed and providing important ecosystem services to the estuarine system, namely nutrient regeneration, primary production and shoreline stabilization as well as a habitat for wildlife (Cacador et al 2009). Estuarine wetlands are known for their high productivity, which has been attributed to the high degree of halophyte coverage and diversity, with specific zonation, resulting from interspecific relationships between species and competition for specific optimal habitats (Mendelssohn and Morris 2000). Another key factor defining species expansion, growth and productivity is their exposure to abiotic stresses, both environmental (for example, climate driven) and anthropogenic (for example, pollution with heavy metals). Taking into account the present projections made by the Intergovernmental Panel for Climate Change (IPCC), it is expected that the increased levels of atmospheric CO2 will lead to an inevitable increase in the dissolved CO2 in water bodies (IPCC 2002), in this way altering the availability of CO2 underwater
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