Combined effect of salt and drought on boron toxicity in Puccinellia tenuiflora

Boron toxicity is a worldwide problem, usually accompanied by salt (NaCl) and drought. The combined stresses may induce complex toxicity to the plant. The aim of the present study was to investigate how the combined stresses of salt and drought affect B toxicity in plants. Puccinellia tenuiflora seedlings were planted in vermiculite. A three (B) × three (salt) × three (drought) factorial experiment (for a total of 27 treatments) was conducted. After a 30-day cultivation, plants were harvested to determine dry weight and the concentrations of B, Na⁺, K⁺, Ca²⁺, and Mg²⁺. Plant growth was inhibited by B toxicity, which was alleviated by salt and drought. B stress enhanced B uptake and transport of the plant, which was inhibited by salt and drought. B stress had a little effect on K⁺ and Na⁺ concentration and caused Ca²⁺ and Mg²⁺ accumulation in the plant. Salt addition increased Na⁺ concentration and inhibited Ca²⁺ and Mg²⁺ accumulation. Drought addition inhibited Na⁺ accumulation and enhanced Ca²⁺ and Mg²⁺ accumulation. The combined stresses of salt and drought had a greater alleviation on the inhibition of dry weight caused by B than individual salt and drought. Besides, the combined stresses of salt and drought also enhanced B uptake and inhibited B transport. The results indicate that salt, drought, and the combined stresses of salt and drought all can alleviate B toxicity in P. tenuiflora, the main mechanism of which is the restriction of B and Na⁺ uptake caused by salt and drought. The combined stresses of salt and drought have a greater effect on B toxicity than individual salt and drought.