Leaf coordination between petiole vascular development and water demand in response to elevated CO₂ in tomato plants

The rise in atmospheric CO₂ has a profound impact on plants physiology and performance. Stomatal gas exchange such as reduction in water loss via transpiration and higher photosynthetic rates are among the key plant physiological traits altered by the increase of CO₂. Water acquired in plant roots is transported via the xylem vessels to the shoots. Under conditions of elevated CO₂, water flux decreases due to higher water use efficiency and a decline in stomatal conductance. However, the mechanism by which the shoot vascular development is affected under elevated CO₂ is still largely unclear in herbaceous crops. In the current study, tomato plants were exposed to either 400 or 800 ppm of CO₂ and were analyzed for growth, leaf area, gas exchange rate, and petiole anatomy. Elevated CO₂ caused a reduction in metaxylem vessel diameter, which in turn, decreased leaf theatrical conductivity by 400% as compared with plants grown under ambient CO₂. This work links anatomical changes in the petioles to the rise in atmospheric CO₂ and water use. Plant water demand declined under elevated CO₂, while photosynthesis increased. Thus, the decrease in leaf specific conductivity was attributed to lower water consumption in leaf gas exchange and, by extension, to higher leaf water use efficiency. As the global climate changes and water scarcity becomes more common, such anatomical alterations caused by elevated CO₂ may affect plant response to water limitation. Further research on petiole anatomical alterations under conditions of combined climate change factors such as drought and heat with elevated CO₂ may assist in clarifying the responses expected by future climate scenarios.