Yield from the shadows: beyond top layer photosynthesis to enhance crop productivity

Photosynthesis research in crops typically focuses on upper canopy layers, which is partly for convenience and partly for the sake of achieving stable datasets under high light conditions. This neglects significant contributions from light - limited portions of the canopy within the lower layers. This study aimed to provide an empirical quantification of the role of these hidden layers of wheat canopies in the context of canopy scale productivity. We demonstrate that light-saturated photosynthetic rates (Asat) in middle and bottom layers at key growth stages can be strong predictors of grain yield. Despite variability in architecture across layers, light interception remained similar and key associations between biomass accumulation and yield with Asat emerged. Yield showed positive associations with photosynthesis in all canopy layers but was stronger at the top layer during grain filling and at the bottom layer during booting. Whole canopy photosynthetic rates were influenced by top layer architecture, N availability in the middle and bottom layers and leaf angles at the bottom of the canopy. Our findings suggest that measurements within hidden layers are required, and that optimizing middle and bottom layer Asat during the vegetative period and top layer Asat during grain filling can boost food security.