Irrigation of hydrangea with saline reclaimed wastewater: Effects of fresh water flushing

In many nurseries in the Mediterranean area, water supply is a major problem and so, agronomical studies into alternative water resources, such as treated wastewater, are of great interest for ornamental plant producers. We conducted a greenhouse study in order to know: (a) the effect of irrigation with saline reclaimed wastewater (RW) on the photochemical behavior, growth and quality of Hydrangea macrophylla Thunb. and (b) the effectiveness of flushing with fresh water (FW) to reduce any negative effects observed with the RW. Potted plants were submitted to three treatments: (1) FW irrigation; (2) RW irrigation; and (3) RW irrigation with FW flushing every three irrigation events (RWFW). Watering with RW (5.65 dS.m-1) severely decreased the size of all aerial organs (leaf, inflorescence and flower), reduced the dry weight of the aerial part by 70%, delayed flowering development and, produced a darker pink color flower compared with the FW treatment. It also caused tip and edge burn in the leaves, the overall effect being a non-commercial plant. RWFW alleviated some of these negative effects, but not sufficiently to avoid a significant loss of plant quality. The evolution of photochemical and gas exchange parameters was determined during one day at the end of experiment. The results indicate strong photochemical activity and gas exchange in the early hours of the morning, both being lower in the plants irrigated with RW. At midday, all plants were stressed, which led the ratio between apparent electron transport rate and net photosynthetic rate (ETR/Pn) being the same in all three treatments. By the end of the afternoon, the photochemical activity had stabilized and the photosynthesis fell, which sharply increased ETR/Pn, indicating that a strong photochemical dissipation was promoted in the plants under both RW and RWFW.