[Trade-offs among light, water and nitrogen use efficiencies of wheat cultivars under different water and nitrogen application levels.]

To study the responses of light use efficiency (LUE), water use efficiency (NUE) and nitrogen use efficiency (NUE) in wheat to water and nitrogen application levels and their interrelationship, a field experiment designed in split-split-plots was conducted with three spring wheat cultivars (Heshangtou, Xihan No.2, Ningchun No.4), under two irrigation levels (full irrigation 4500 m ³ ·hm ^-2 and limited irrigation 3000 m ³ ·hm ^-2 ) and five nitrogen application levels (0, 75, 150, 225, 300 kg N·hm ^-2 ). The results showed that LUE, WUE and NUE of three wheat cultivars differed significantly. The LUE increased as irrigation and nitrogen quantity increased in a certain range, but decreased under excessive nitrogen application. The WUE of strong and moderate drought resistant cultivars (Hsahangtou and Xihan No.2) were less affected by irrigation than non-drought resistant cultivar (Ningchun No.4). Nitrogen application could regulate WUE of wheat, and the highest WUE at medium nitrogen levels (strong and moderate drought resistant cultivars in 150 kg·hm ^-2 , non-drought resistant cultivar in 225 kg·hm ^-2 ). As the nitrogen application level increased, nitrogen accumulation in plants increased first and then decreased, nitrogen dry matter production efficiency (NUE _b ), nitrogen harvest index (NHI), nitrogen agronomic use efficiency (NAE), and nitrogen partial factor productivity (PFP) were all decreased significantly. Irrigation had no significant effect on NHI. As the irrigation level increased, nitrogen accumulation of wheat increased significantly, the NUE _b and NAE of strong and moderate drought resistant cultivars decreased significantly, the NUE _b and PFP of the non-drought resistant cultivars increased significantly, while it had no significant effects on other indicators. Extremely significantly negative correlation between nitrogen acquisition ability and nitrogen use efficiency was found in all three wheat cultivars, and NUE _b was significantly negatively correlated with LUE and WUE, LUE was significantly positively correlated with WUE, demonstrating clear trade-offs among nitrogen use efficiency to light use efficiency and water use efficiency of spring wheat. Higher resource utilization efficiencies were achieved under irrigation of 3000 m ³ ·hm ^-2 , and application of 150 kg N·hm ^-2 for strong and moderate drought resistant cultivars and 225 kg N·hm ^-2 for non-resistant cultivar.