Effect of nursery irrigation regimes on vegetative growth and root development of Silene vulgaris after transplantation into semi-arid conditions

The influence of irrigation regimes during nursery production of seedlings on development of the aerial parts and root system after being transplanted into semi-arid conditions was investigated in Silene vulgaris (Moench.) Garcke. This Mediterranean native herb is of interest for phytoremediation of contaminated soils and for edible and medicinal uses. During the 35 d nursery period, seedlings were grown in polystyrene trays. Three irrigation treatments were used throughout the nursery period: WI, well-irrigated seedlings; MS, moderately-stressed seedlings; and HS, highly-stressed seedlings. In all treatments, seedlings were overhead irrigated on 2 d per week, and the total amounts of water applied (per tray of 176 seedlings) over the whole nursery period were: W1, 16.10 1; MS, 10.75 1; and HS, 4.50 1. After the nursery period, WI and MS plants were transplanted into transparent containers (cylindrical acrylic tubes, 8 cm in diameter and 100 cm tall) and into the field, where mini-rhizotrons were used to evaluate root system dynamics. Plants transplanted into containers were watered with two irrigation regimes: normal irrigation (NI) and deficit irrigation (DI), with 0.90 or 0.45 1 plant(-1) week(-1), respectively. All plants transplanted into the field were watered equally, with 1.16 1 plant(-1) week(k-1). Post-transplantation growth of aerial parts and roots was studied over 120 d in the transparent containers and over 60 d in the field. MS and HS treatments during the nursery period produced seedlings that showed lower midday leaf water potential and greater root:aerial parts fresh weight (FW) ratios than the WI treatment. The MS treatment produced seedlings with the greatest length and FW of roots and with the highest quality. The HS treatment produced seedlings which were too small and over-hardened. The latter were therefore not used for post-transplantation experiments. After transplantation into transparent containers, MS seedling-derived plants showed greater root growth than WI-derived plants, especially when the water content of the substrate was low (DI treatment). Also, mini-rhizotrons allowed observation of more active root growth in MS seedling-derived plants than in WI seedling-derived plants after transplantation into the field, especially in the deepest layer of soil (50-75 cm). WI-derived and MS-derived plants, under NI or DI post-transplantation treatments, showed similar FWs and dry weights (DWs) of their aerial parts, but MS-derived plants showed greater leafistem FW and DW ratios than WI-derived plants under DI conditions.