Radial oxygen loss, a plastic property of dune slack plant species

Abstract

Mean and environmentally induced differences in radial oxygen loss (ROL) were investigated for three pioneer species (i.e. Schoenus nigricans L., Juncus articulatus L. and Samolus valerandi L.) and two late-successional dune slack species (i.e. Calamagrostis epigejos L. and Carex flacca Schreber). These species were grown in a factorial design at conditions differing in moisture, light, nutrient availability and Fe²⁺ and Mn²⁺ concentrations. On average, ROL was twice as low for late-successional species compared to pioneer species, but it increased on average by a factor 1.5 for these species upon flooding while ROL was unaffected by flooding in pioneer species. Other effects of treatments on pioneer and late-successional species groups were insignificant. Species-specific plasticity in ROL was stronger than that of the species groups and varied highly with the different combinations of – interactions between – environmental cultivation conditions flooding, concentrations of Fe²⁺ and Mn²⁺, nutrient and light levels, but was not affected by differences in relative growth rates. Moreover, ROL activity was almost 20×, and significantly, higher for seedlings than for adults of Schoenus nigricans. This implies that ROL of a species depends on the stage of the life cycle and on growth conditions, something that should be considered when determining ROL. ROL activity of most species increased at (a combination of) high nutrient and at low light levels: ROL activity was strongly negatively correlated to the root/shoot ratio, which was presumably caused by a higher gas transport capacity compared to root oxygen consumption at low root/shoot ratios. The plasticity in ROL leads to a highly dynamic rhizosphere in which the oxygen influx is a function of plant species and particularly of the interactions between plant species and environmental conditions.