Leaf senescence, nitrogen remobilization, and productivity of maize in two semiarid intercropping systems

It is unclear how interspecific resource competition affects crop leaf senescence in association with nitrogen (N) remobilization and overyielding in semiarid intercropping systems. To address this issue, maize intercropped with soybean (weakly competitive species) and wheat (strongly competitive species) was examined across three consecutive years to explore the effects of resource competition on maize relative and absolute yield gain, leaf senescence traits, N remobilization and physiological activities in a typical semiarid site. High yield (171.8 g plant-1), relative yield (0.63) and net effect (0.99 t ha-1) of maize were observed in the maize-soybean intercropping system, while the opposite trend was found in the maize-wheat intercropping systems. Overall, maize benefited from intercropping with soybean but was negatively affected by intercropping with wheat. Interestingly, both intercropping systems significantly delayed the onset time of maize leaf senescence by approximately 5-20 days and prolonged the senescence duration by approximately 8-18 days. Intercropping with soybean increased maize leaf dry matter remobilization from 7.3 to 12.5 g per plant-1 and reduced N remobilization from 0.81 to 0.45 g plant-1, respectively. However, when intercropped with wheat, dry matter and N remobilization of maize leaves were decreased, at 4.8 and 0.13 g plant-1, respectively. Therefore, excessive delay and prolonged leaf senescence reduced leaf dry matter translocation and N to the grain which impaired yield formation. Our findings provided novel insights into the physiological mechanism of overyielding from the perspective of leaf senescence traits and remobilization function in the semiarid intercropping systems.