Arbuscular mycorrhizal symbiosis improves tolerance of Carrizo citrange to excess boron supply by reducing leaf B concentration and toxicity in the leaves and roots

This study explores the possibility of using mycorrhization as a novel technique for diminishing the negative effects of boron (B) in the nutrient solution on seedlings of Carrizo citrange rootstock plants. For this, an experiment was planned for studying the physiological (gas exchange and chlorophyll fluorescence parameters), morphological (vegetative growth parameters), nutritional (organic solutes, carbohydrates) and oxidative stress responses of seedlings that were either mycorrhized (+AM, Rhizophagus irregularis; previously known as Glomus intraradices) or not mycorrhized (-AM), and irrigated with water containing different concentrations of B (0.5, 5 and 10 mg L−1). It was observed that an excess of B in the nutrient solution decreased the vegetative growth in both +AM and -AM plants, but this decrease was greater in -AM plants. Mycorrhized plants (+AM) under high B concentration accumulated less B in the leaves, and had a smaller reduction of net assimilation rate of CO2 and lower MDA concentration than non-mycorrhized plants. Thus, it can be concluded that mycorrhization increased the tolerance to high boron concentration in the irrigation water of citrange Carrizo seedlings by reducing both the B concentration in the plant tissue and the B toxicity in the physiological processes. The study of organic solutes and carbohydrates also pointed to a different response model between +AM and -AM plants that could be related to the different tolerance observed between these plants. •The tolerance to excess boron was studied in mycorrhized Carrizo citrange plants grown under greenhouse with three B concentrations (0.5, 5 and 10 mg L−1).•High B in the nutritive solution did not affect the percentage of mycorrhization, but it did affect the proliferation within the roots.•Mycorrhized plants were more tolerant to B than non-mycorrhized, because mycorrhized plants had a low leaf B concentration, and B toxicity decreased.•Study about soluble and reducing sugars suggest that carbohydrates play a decisive role in the tolerance of mycorrhized plants.