Is elongation-induced leaf emergence beneficial for submerged Rumex species?

Plant species from various taxa 'escape' from low oxygen conditions associated with submergence by a suite of traits collectively called the low oxygen escape syndrome (LOES). The expression of these traits is associated with costs and benefits. Thus far, remarkably few studies have dealt with the expected benefits of the LOES. Young plants were fully submerged at initial depths of 450 mm (deep) or 150-240 mm (shallow). Rumex palustris leaf tips emerged from the shallow flooding within a few days, whereas a slight lowering of shallow flooding was required to expose R. acetosa leaf tips to the atmosphere. Shoot biomass and petiole porosity were measured for all species, and treatments and data from the deep and shallow submergence treatments were compared with non-flooded controls. R. palustris is characterized by submergence-induced enhanced petiole elongation. R. acetosa lacked this growth response. Upon leaf tip emergence, R. palustris increased its biomass, whereas R. acetosa did not. Furthermore, petiole porosity in R. palustris was twice as high as in R. acetosa. Leaf emergence restores gas exchange between roots and the atmosphere in R. palustris. This occurs to a much lesser extent in R. acetosa and is attributable to its lower petiole porosity and therefore limited internal gas transport. Leaf emergence resulting from fast petiole elongation appears to benefit biomass accumulation if these plants contain sufficient aerenchyma in petioles and roots to facilitate internal gas exchange.