CO2 GAS-EXCHANGE OF 2 INTERTIDAL SEAGRASS SPECIES, ZOSTERA-MARINA L AND ZOSTERA-NOLTII HORNEM DURING EMERSION

CO2 ps exchange of emersed Zostera marina L. and Zostera noltii Hornem. plants was measured with a portable infrared ps analysis system in the intertidal flats of Sylt (Southern North Sea). Light-saturated net photosynthesis rates during emersion were found to be in the same magnitude as values reported in the literature for both species under submersed conditions at various locations. Net photosynthesis of exposed shoots of Z. noltii showed a very low light-compensation point, a high light-saturation value, and a light-saturated assimilation rate nearly twice as high as for co-occurring Z marina plants. Artificial drying of the leaves of Z marina in the air stream of the gas exchange cuvette led to a continuous reduction in the light-saturated net photosynthesis rate that was partly reversible after re-wetting of the leaves. More research is needed to qualify whether intensive photosynthetic activity is a common phenomenon in emersed intertidal seagrass populations and how significant this process is for the carbon balance of these plants.