Multigenerational Effects of Elevated CO2 and N Supply on Leaf Gas Exchange Traits in Wheat Plants

The responses of leaf gas exchange of wheat (Triticum aestivum L.) to elevated atmospheric CO₂ concentration (e[CO₂]) were often investigated within a single generation, while the long-term acclimation of photosynthesis to growth in e[CO₂] over multiple generations has not been systematically studied. Here, five wheat cultivars were grown under either ambient (a[CO₂], 400 ppm) or elevated (e[CO₂], 800 ppm) CO₂ concentration for three consecutive generations (G1 to G3) with two N-fertilisation levels (1N–1 g N pot⁻¹ and 2N–2 g N pot⁻¹) in climate-controlled greenhouses. Leaf gas exchange was determined in each generation of plants under different treatments. It was found that at both N levels, e[CO₂] stimulated photosynthetic rate while reducing stomatal conductance, transpiration rate and leaf N concentration, resulting in an enhanced water use efficiency and photosynthetic N use efficiency. The N level modulated the intergenerational responses of photosynthetic capacity to e[CO₂]; under low N supply, the maximum carboxylation rate (V_cmax), the maximum electron transport rate (J_max) and the rate of triose phosphate utilisation (TPU) were significantly downregulated by e[CO₂] from the first to the second generation, but recovered in the third generation; whereas at high N levels, photosynthetic acclimation was diminished with the progress of generations, with V_cmax, J_max and TPU increased under e[CO₂] in the third generation. These results suggest that intergenerational adaptation could alleviate the e[CO₂]-induced reduction of the photosynthetic capacity, but plants with different N status responded differently to adapt to the long-term exposure to e[CO₂]. Among the five cultivars, 325Jimai showed a better photosynthetic performance under e[CO₂] over the three generations, while 02-1Shiluan appeared to be more inhibited by CO₂ elevation in the long term conditions. These findings provide new insights for breeding strategies in the future CO₂-enriched environments.