Phenotyping canopy-level photosynthetic responses to intermittent shading: beyond the daily light integral in multilayered cropping systems

Multilayered cropping systems such as agrivoltaics, agroforestry, and intercropping create spatiotemporal light variability, including daily shade intermittence. While its physiological impacts are recognised, shade intermittence remains understudied and is not accounted for in crop models, which typically consider a daily light integral (DLI) to calculate growth. Beyond photosynthetic adjustments to rapid light changes, it also affects integrative traits such as plant morphology and reduces radiation use efficiency (RUE) compared to constant shading. In a recent study across 14 rice genotypes, intermittent shading compared to constant shading with the same DLI, significantly reduced yield and aboveground biomass. Source limitations were driven by the nonlinear light- assimilation response combined with a decrease in photosystem efficiency (ΦPSII and electron transport rates) under both low and high light levels. Crop responses were consistent among genotypes, but biomass and yield varied widely. These findings emphasise the need to consider not just DLI but also shading dynamics when phenotyping crop responses in partial shade. Moreover, plant responses to shade intermittence vary with shading intensity, frequency, and duration. This raises a key question: how can shading dynamics be integrated into phenotyping and modelling approaches? To address this, we combined canopy assimilation measurements (flux chamber) under four daily shading patterns, created with removable shade nets, and leaf-level fluorescence and gas exchange measurements (Li-6800) on two rice varieties. Objectives include observing canopy assimilation dynamics under various shading patterns, identifying traits relevant for phenotyping rice photosynthesis under intermittent shading, and determining shading pattern variables that explain these responses for consideration into modelling. First results provide insight into key traits for phenotyping rice performance under intermittent shade and identify shading pattern indexes explaining assimilation variation. This novel approach to phenotyping photosynthesis traits under intermittent shading opens new possibilities for improving genotype selection and optimising multilayered system design.