Chloride Application Enhances Photosynthesis and Facilitates Nitrate Translocation While Driving Chloride Translocation Into Roots

Chloride and nitrate are essential mineral elements for crop growth. Due to their similar physical and electrochemical properties, their uptake and translocation interact antagonistically. This suggests that applying chloride to the leaf canopy during the late grain-filling stage of cereals might enhance nitrate use efficiency. Hence, it remains uncertain whether foliar-applied chloride at the late growth stage stimulates nitrate translocation from mature to younger leaves. To explore this possibility, two contrasting faba bean varieties were grown in a climate-controlled chamber. Nitrate concentrations of approximately 50 and 93 μg mg FW⁻¹, respectively, were established in leaves by depleting nitrogen in the rooting medium. Based on these two nitrate concentrations in mature leaves, chloride was applied to the leaf canopy. Measurements of biomass, photosynthesis, and nitrate and chloride concentrations in both young and mature leaves revealed that chloride foliar application raised nitrate levels in younger leaves from 7.1 to 9.5 μmol g FW⁻¹ and boosted photosynthesis by approximately 35%. However, one of the two faba bean varieties did not respond significantly to the chloride foliar application. These findings indicate that chloride application facilitates nitrate translocation from mature to younger leaves, potentially improving grain nitrogen supply. As a result, nitrate use efficiency might be increased by chloride application during late growth stages, although this effect is genotype-dependent.