Chloride as a macronutrient increases water‐use efficiency by anatomically driven reduced stomatal conductance and increased mesophyll diffusion to CO2
Franco‐Navarro, Juan D. | Rosales, Miguel A. | Cubero‐Font, Paloma | Calvo, Purificación | Álvarez, Rosario | Diaz‐Espejo, Antonio | Colmenero‐Flores, José M.
Chloride (Cl⁻) has been recently described as a beneficial macronutrient, playing specific roles in promoting plant growth and water‐use efficiency (WUE). However, it is still unclear how Cl⁻ could be beneficial, especially in comparison with nitrate (NO₃⁻), an essential source of nitrogen that shares with Cl⁻ similar physical and osmotic properties, as well as common transport mechanisms. In tobacco plants, macronutrient levels of Cl⁻ specifically reduce stomatal conductance (gₛ) without a concomitant reduction in the net photosynthesis rate (AN). As stomata‐mediated water loss through transpiration is inherent in the need of C₃ plants to capture CO₂, simultaneous increase in photosynthesis and WUE is of great relevance to achieve a sustainable increase in C₃ crop productivity. Our results showed that Cl⁻‐mediated stimulation of larger leaf cells leads to a reduction in stomatal density, which in turn reduces gₛ and water consumption. Conversely, Cl⁻ improves mesophyll diffusion conductance to CO₂ (gₘ) and photosynthetic performance due to a higher surface area of chloroplasts exposed to the intercellular airspace of mesophyll cells, possibly as a consequence of the stimulation of chloroplast biogenesis. A key finding of this study is the simultaneous improvement of AN and WUE due to macronutrient Cl⁻ nutrition. This work identifies relevant and specific functions in which Cl⁻ participates as a beneficial macronutrient for higher plants, uncovering a sustainable approach to improve crop yield.
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