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 (NO
3?), 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 C
3 plants to capture CO
2, simultaneous increase in photosynthesis and WUE is of great relevance to achieve a sustainable increase in C
3 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 CO
2 (
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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