Yield more in the shadow: Mitigating shading-induced yield penalty of maize via optimizing source-sink carbon partitioning

Global solar radiation has been decreasing, posing a great threat to food security by reducing photo-assimilation and disrupting carbon (C) partitioning in crops like maize. However, practical countermeasures to cope with source-sink balance in periodic shading stress are lacking. Here, we first simulated shading stresses with different degrees and occurring periods on field maize for two years. Results verified that shading-induced yield penalties are most severe around silking and are closely associated with biomass allocation, implying a significant imbalance of source: sink C partitioning during silking. To mitigate yield losses from shading, detasseling (Det) and synchronous pollination (SP), targeting the two sink tissues (tassel and ear, respectively), were applied to 70 % shading at the silking stage in two seasons. Both practices conferred benefits to grain number and yield production, with final yield increases ranging from 4.0 % to 31.3 % under shading. Through ¹³C labeling, sugar metabolism assay and global analysis, we proved that Det improved the source-sink balance via increasing light irradiance within the canopy and eliminating apical dominance to stimulate C assimilates partitioning into the ear. SP promoted C partitioning into the ear by increasing reproductive sink strength and optimizing assimilates allocation among grain siblings. Intriguingly, Det and SP also provided marginal yield increase under normal light conditions. Our findings underscore the potential of source-sink coordination and C partitioning in mitigating maize yield penalty under environmental stresses like shading. The research also provides new avenues for developing agronomic practices and breeding strategies via tasseling and silking regulation, aiming to improve maize crop production and stress resilience and ensure food security in the face of climate change.