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.