Root-zone biopolymer application improves drought resilience, water-use efficiency and recovery of Bougainvillea spectabilis

Water shortage is becoming a challenge for ornamental plants, especially in arid and semi-arid regions where a significant amount of irrigation is required to maintain attractive landscapes.Bougainvillea spectabilis is well adapted to warm climates and widely used in landscapes where water is limited, but prolonged drought can limit vegetative growth, photosynthesis, flowering and overall ornamental quality.The present study investigated a root-zone strategy to improve drought tolerance by combining the water-holding capacity of a biodegradable hydrogel with the biological activity of alginate oligosaccharide (AOS) and chitosan.Plants were subjected to three water regimes corresponding to 100%, 70% and 40% field capacity and were subjected to one of four treatments: untreated control, alginate hydrogel, AOS or AOS incorporated into a chitosan-based hydrogel.Growth, flowering, photosynthetic pigments, gas exchange, leaf water relations, osmotic adjustment, oxidative stress, antioxidant enzymes, root architecture, and water use efficiency were measured.A seven-day period of rewatering was then employed to assess the recovery of plants from severe drought.Water deficiency decreased plant height, branching, leaf area, biomass, chlorophyll concentration, photosynthetic rate, stomatal conductance and relative water content in a progressive manner.It also enhanced hydrogen peroxide, malondialdehyde (MDA) and electrolyte leakage.The combined AOS + chitosan treatment was the best protection, especially under severe drought conditions.Leaf water content, photosynthetic activity and root development of the treated plants at 40% field capacity were significantly higher than the untreated plants.The treatment also increased proline, soluble sugars and glycine betaine accumulation and SOD, CAT and APX activities, decreased oxidative membrane damage.After rewatering, AOS +chitosan-alginate hydrogel-treated plants recovered faster, had higher relative water content and photosynthetic activity, and lower MDA and electrolyte leakage than untreated drought-stressed plants.In general, these results indicate that the use of a water-retaining root-zone hydrogel in conjunction with AOS and chitosan can confer physical and physiological protection against drought.This strategy can be useful to improve the performance and water use efficiency of Bougainvillea under intermittent irrigation in dry environments.