High‐Nitrogen Supply Enhances Leaf Photosynthesis Capacity of Chickpea ( Cicer arietinum L.) Under Elevated CO ₂

Background Nitrogen (N) limitation may reduce the CO 2 ‐fertilization effect on photosynthesis and crop productivity. The mechanisms by which N supply influences photosynthetic capacity under elevated CO 2 (eCO 2 ) are not well understood, particularly in chickpea. Aims This study examined the interactive effects of CO 2 and N supply on chickpea's photosynthetic capacity and leaf N status, and to understand the regulatory role of N in photosynthetic capacity under eCO 2 . Methods Non‐inoculated chickpea plants were grown under two CO 2 levels (400 vs. 800 µmol mol −1 ) and two N rates (21 vs. 189 mg N kg −1 soil) for 65 days. Photosynthetic activity and plant N uptake were investigated at the flowering and podding stages of growth. Results Adequate N supply maintained the maximum Rubisco carboxylation capacity ( V c,max25 ) and the electron transport rate supporting ribulose–1,5‐bisphosphate (RuBP) regeneration ( J 25 ) under eCO 2 by increasing leaf N concentration per unit area and chlorophyll synthesis and reducing photosynthetic acclimation in chickpea under eCO 2 at the flowering and podding stages. Low N decreased the leaf N concentration and SPAD (soil and plant analyzer development of chlorophyll meter readings) and limited the eCO 2 ‐driven increases in V c,max25 and J 25 . High‐N supply increased plant biomass and N accumulation to a greater extent under eCO 2 than under ambient CO 2 , leading to significant CO 2 × N interactions. Conclusion Adequate N supply is critical to enhance photosynthetic capacity by maintaining V c,max25 and J 25 in non‐inoculated chickpea at the flowering and podding stages under eCO 2 . The findings highlight the importance of optimizing N management for maximizing the CO 2 ‐fertilization effect in future climate change.