Photosynthesis response to severe water deficit in terminal stems of Myriolimon ferulaceum

Myriolimon ferulaceum is a leafless species and close relative to Limonium inhabiting the same harsh environments in the rocky coast and salt marshes, with discontinuous distribution in western and central coast of the Mediterranean Basin and southern Iberian Peninsula. In order to test for the drought adaptive importance of photosynthesis in stems, and to decipher advantages and drawbacks of stem vs. leaf photosynthesis under drought conditions, M. ferulaceum was grown under the well-watered and severe water deficit conditions used in previous experiments with Limonium. Growth, stem anatomy, photosynthesis and gas exchange, and Rubisco-related traits were measured. Growth capacity in M. ferulaceum was higher than that of many Limonium under well-watered conditions, where limitations to photosynthesis were mostly biochemical. However, severe water deficit conditions had a higher impact in the leafless species, where the main photosynthesis limitation was stomatal conductance. High intrinsic water-use efficiency under well-watered conditions and high mesophyll conductance to stomatal conductance ratio under severe water deficit conditions were the main drivers of growth capacity in M. ferulaceum.