Irrigating with high boron concentration improved the physiological response of ‘Carrizo’ citrange seedlings under drought stress and recovery conditions

Boron (B) is an essential plant micronutrient. Citrus are widely cultivated in semi-arid areas, where they are commonly exposed to temporary water scarcity and irrigated with non-conventional waters (such as reclaimed water and desalinated seawater) with high boron concentration. Thus, this study aimed to determine the physiological alterations generated by applying a cycle of drought stress and recovery in ‘Carrizo’ citrange (Citrus sinensis (L.) Osb. × Poncirus trifoliata L.) seedlings irrigated with different boron concentrations to evaluate their combined effects on leaf water relations and photosynthetic parameters. Seedlings were grown in controlled conditions and were well-watered with low B (0.11 mg L^‑1) and high B (5 mg L^‑1) concentrations. After 20 days, half of the plants were drought-stressed (DS) by withholding irrigation for 10 days, while the other half were maintained well-watered (WW) with low or high B. After the drought period, half of the plants were harvested, and the other half were re-irrigated with low B. The main results have shown that high B in WW plants enhanced the accumulation of B in leaves, and it affected the plant water status and decreased photosynthesis rate, mainly due to a partial stomatal closure. Photosynthesis similarly decreased in low and high B DS plants. Nevertheless, high B maintained better leaf water status in DS plants, which enhanced the complete and rapid recovery of the plant water status and gas exchange after re-irrigation. In contrast, in low B and DS plants, the stress level reached was higher than in high B-DS plants. This fact impeded the physiological recovery after the water restitution. In conclusion, plants preconditioned by high B maintained a better plant water status under drought stress due to a partial stomatal closure, and it allowed the full recovery of plant water status after re-irrigation with low boron concentration.