The researchers studied different types of wheat to see how well they could absorb carbon from photosynthesis when given different amounts of nitrogen. They found that wheat varieties with high nitrogen efficiency had the best grain yield and nitrogen use efficiency, along with higher photosynthetic rates and certain enzyme activities in their leaves. These varieties also had better performance under nitrogen-deficient conditions. However, there was no consistent pattern for other traits like chlorophyll content or stomatal conductance. Overall, the wheat variety with high nitrogen efficiency performed the best under nitrogen stress, while the variety with middle nitrogen efficiency did the best under nitrogen-rich conditions.