Effect of deficit irrigation on visual quality, physiological responses, and water use efficiency of Ranunculus asiaticus L.

Water scarcity is one of the major environmental stresses that adversely affect physiological processes and plant growth. Deficit irrigation (DI) is one of the important irrigation management strategies that has been proposed to conserve water, whereas plants are exposed to a certain degree of water stress. The purpose of the present study was to identify physiological and morphological responses of Ranunculus to different levels of deficit irrigation.

The pot experiment was arranged in the greenhouse in a completely randomized design with four replicates. Plants were irrigated under four water regimes included (1) the control (100% SWC), with full irrigation, in which the soil water content was maintained at 100% pot capacity throughout the plant growth period, (2) the low deficit irrigation (75% SWC) in which the soil water content was retained at 75% of the pot capacity, (3) the moderate deficit irrigation (50% SWC) in which the soil water content remained at 50% of the pot capacity, and (4) severe deficit irrigation (25% SWC) in which the soil water content maintained at 25% of the pot capacity. In this study growth parameters (plant height, number of leaves, number of buds, flowers and petals, petiole length, fresh and dry weight of shoots and underground organs), physiological attributes (electrolyte leakage, relative water content), photosynthesis parameters (transpiration rate, leaf temperature, intercellular CO2 concentration, ambient CO2 concentration), water use efficiency (WUE) and degree of tolerance to deficit irrigation stress of Ranunculus plants were evaluated.

The results showed that severe DI reduced plant height (34.5%), leaf number (57%), petiole length (47%), bud number (233%), flower diameter (23%), number of petals (17%), fresh and dry weight of aerial parts (59%, 53%), fresh and dry weight of underground parts (69%, 77%) compared to stress-free conditions (100% SWC). These symptoms indicated the adverse effects of deficit irrigation on the plant. As a consequence of this, leaf temperature (31.90°C), ambient CO2 concentration (479.06 µmol.m‐2.s‐1), and intracellular CO2 (479.47 µmol.m‐2.s‐1) were higher in severe DI. Plants subjected to full irrigation, and low deficit irrigation (75% SWC) had more flowers bud than moderate and severe water stress. Findings of the experiments revealed that low deficit irrigation slightly decreased the plant height, leaf number, petal number, and plant biomass than full irrigation conditions. Also, the highest transpiration rate (0.88 µmol.m‐2.s‐1) was observed at a moderate DI (50% SWC). In addition, plants submitted to an irrigation water deficit have lower values relative water content (RWC) than those of fully irrigated plants. Severe DI (25% SWC) caused a remarkable increase in electrolyte leakage followed by 50% SWC. It was found that WUE decreased with an increase in water stress levels. The WUE was higher (37.5%) in full irrigation than in moderate and severe deficit irrigation. Moreover, by implementing DI, irrigation at 25% SWC for Ranunculus plants saved 45.78% of water.

In general, these results show that Ranunculus is sensitive to severe deficit irrigation stress and is moderately tolerant to 75% SWC. Therefore, low deficit irrigation (75% SWC) stress, but not moderate or severe, could be imposed in Ranunculus to reduce water consumption, still maintaining plant ecophysiological performances and ornamental quality.