Nursery irrigation regimes affect the seedling characteristics of Silene vulgaris as they relate to potential performance following transplanting into semi-arid conditions

The influence of pre-conditioning water regimes during nursery production on seedling characteristics was investigated in Silene vulgaris (Moench.) Garcke. Two experiments were carried out. In Experiment 1, throughout the nursery period (5 weeks), seedlings growing in polystyrene trays were overhead-watered twice a week using three irrigation treatments: WW (well-watered), irrigated to 75% of the water-holding capacity (WHC); MS (moderately-stressed), watered to 50% of the WHC and HS (highly-stressed) watered to 15% of the WHC. At the end of the nursery period, seedlings raised under the MS treatment showed greater total root lengths, specific root lengths (SRL), degrees of root branching, root fresh weights (FW) and dry weights (DW), root DW:volume ratios, and water-use efficiencies (WUE) than those raised under the WW treatment. The MS seedlings were shorter, had a lower midday leaf water potential, and had lower shoot:root FW and DW ratios than the WW seedlings. Irrigation regime had no influence on the suberisation of roots, but the taproots of WW seedlings showed a lower cortex thickness:root radius (C:R) ratio (0.102) than taproots of MS and HS seedlings (0.125 and 0.136, respectively). HS seedlings were too small (1.9 cm high) and over-hardened, with poorly developed root systems. Experiment 2 (identical to Experiment 1 but using only two irrigation regimes: WW and MS) confirmed the differences observed in shoot and root growth between WW and MS seedlings.