Root plasticity in Mediterranean herbaceous species

Root plasticity has been largely studied on herbaceous species of north European temperate flora and is defined as the ratio between root depth in dry soils and root depth in wet soils. In summer dry habitats such as Mediterranean environments, the soil water deficit is a common feature to which root systems of plant species should adapt to improve their ecological efficiency. The aim of this study was to compare root plasticity in annual Mediterranean species that regenerate exclusively from seeds, and herbaceous perennial Mediterranean species that use dual regeneration strategies. Root plasticity of ten herbaceous species, six perennials and four annuals, was compared in this study. The annuals species studied occur in lowland Mediterranean grasslands referred to Tuberarietea guttatae class (Dasypyrum villosum, Lophochloa pubescens, Ornithopus compressus, Rumex bucephalophorus), while the perennial species occur in montane sub-Mediterranean grasslands referred to Festuco brometea (Bromus erectus, Festuca ovina., Lotus corniculatus., Minuartia verna, Sanguisorba minor, Thymus longicaulis). The examined species were subjected to water stress according to standard methods applied in comparative ecology, i.e., half of the seedlings of each species received 20 ml de-ionized water daily for three weeks, while the other half did not. After seedling harvesting the following parameters were analysed: (i) total root length; (ii) root length in the first 10 cm of soil; (iii) shoot height; (iv) root biomass in the first 10 cm of soil; (v) shoot biomass; (vi) shoot and root plasticity. Results show that root plasticity increased significantly in dual-regenerator sub-Mediterranean mountain species