Multigenerational Effects of Elevated CO 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 CO concentration (e[CO]) were often investigated within a single generation, while the long-term acclimation of photosynthesis to growth in e[CO] over multiple generations has not been systematically studied. Here, five wheat cultivars were grown under either ambient (a[CO], 400 ppm) or elevated (e[CO], 800 ppm) CO concentration for three consecutive generations (G1 to G3) with two N-fertilisation levels (1N–1 g N pot and 2N–2 g N pot) 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[CO] 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[CO]; under low N supply, the maximum carboxylation rate (V), the maximum electron transport rate (J) and the rate of triose phosphate utilisation (TPU) were significantly downregulated by e[CO] 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, J and TPU increased under e[CO] in the third generation. These results suggest that intergenerational adaptation could alleviate the e[CO]-induced reduction of the photosynthetic capacity, but plants with different N status responded differently to adapt to the long-term exposure to e[CO]. Among the five cultivars, 325Jimai showed a better photosynthetic performance under e[CO] over the three generations, while 02-1Shiluan appeared to be more inhibited by CO elevation in the long term conditions. These findings provide new insights for breeding strategies in the future CO-enriched environments.