Chloride as a macronutrient increases water‐use efficiency by anatomically driven reduced stomatal conductance and increased mesophyll diffusion to CO₂

Abstract

Summary 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.

Metabolic Insights into the Anion-Anion Antagonism in Sweet Basil: Effects of Different Nitrate/Chloride Ratios in the Nutrient Solution

“…We employed chlorine concentrations that were not expected to induce visible toxicity symptoms (e.g., chlorosis, leaf tip burning, stunting, etc.) [28]. In addition to an anion-anion competition, the linear decrease of the nitrate concentration from highest to intermediate NS ratios is likely to be due also to the chloride interference with several steps of nitrogen utilization (e.g., uptake, assimilation, translocation and remobilization).…”

“…It is well known that the interplay between these signal molecules involves a number of plant functions, and therefore, the crosstalk between the nitrate, NO and phytohormones signaling pathways chains the multifaceted and complex metabolomic signatures we observed [46,[54][55][56] In conclusion, our work indicated that the interplay between nitrates and chlorines exerts a large effect on basil yield and metabolomic profile, that cannot be satisfactorily explained only by an anion-anion antagonist outcome (e.g., a replacement effects and carrier competition processes). Considerable changes were observed in a number of chemical classes and their relation with the different nutrient ratios suggests a dose-dependent effect that is mainly the combination of a response to nutrient availability (e.g., primarily nitrogen) [56] and an inducible response to stress, which is evident when chloride concentration in the nutrient solution exceeds that which is capable to satisfy nutrient requirements [28]. Our work highlighted the potential and the magnitude of the effect of NS management for leafy vegetables.…”

Determining Ion Toxicity in Cucumber under Salinity Stress

“…This indicates that osmotic effects of the Cl − dominant solution on leaf expansion and light interception were not prominent and the differences in plant dry mass between the control and Cl − dominant treatment mainly resulted from the osmotic effects on leaf photosynthesis, which reduced photosynthesis rate by 13% and 11% in Aramon and Line-759, respectively, according to the value of O s in Equations (2) and (3). Since Cl − can be used by the plant as an osmoregulator to promote leaf expansion, the insignificant difference in total leaf area between the control and Cl − dominant solution was probably a counterbalance between the negative effects of osmotic stress and the positive effects of Cl − on leaf cell expansion [36,37]. It is also interesting that cucumber seems to have mechanisms avoiding overaccumulation of Cl − .…”

Coping With Water Shortage: An Update on the Role of K+, Cl-, and Water Membrane Transport Mechanisms on Drought Resistance

“…The beneficial effect of macronutrient Clnutrition in maintaining high photosynthesis rates while improving WUE is particularly challenging in C 3 plants, in which water loss through transpiration is inherent to the process of fixing atmospheric CO 2 . This is because Clspecifically increases the mesophyll diffusion conductance to CO 2 (Franco-Navarro et al, 2019;Maron, 2019). This is a consequence, at least in part, of a higher surface area of chloroplasts exposed to the intercellular airspace of mesophyll cells.…”