Phenotypic plasticity and acclimation to water deficits in velvet-grass: a long-term greenhouse experiment. Changes in leaf morphology, photosynthesis and stress-induced metabolites

Wild velvet-grass (Hocus lanatus) collected from a natural population along a drought gradient, previously demonstrated as genetically homogeneous, was studied for phenotypic plasticity and acclimation mechanisms to water deficits. A three months greenhouse experiment was designed with plants submitted to nine levels of water availability, three months being the usual length of summer drought in field conditions. Aboveground biomass, total soluble proteins, free proline, free polyamines, leaf morphology, stomatal and hair characteristics, and net photosynthetic rates were analysed, and their significance discussed. Moderate drought did not damage the velvet-grass, and the plants grew better than without water limitation. Water stress-typical responses were shown as time and severity dependent in all the measured parameters. Lowest water availability treatments induced significative increase in free proline and soluble protein contents, as well as reductions in leaf size and aboveground biomass. Spermidine contents rose significatively in the most severe water stress. Furthermore, velvet-grass acclimated progressively to long-term water limitation.