Beyond light quantity: Intermittent shading affects growth and yield more than constant shading in rice cultivars

Plant responses to shade are often studied under constant light reduction, but rarely under intermittent shading which is frequent in natural environments and multilayered systems such as agrivoltaics and agroforestry. We investigated in controlled environments how a 38 % reduction in daily radiation, applied either continuously or as several intermittent periods per day, affected morphology, phenology, aboveground biomass, yield components, and photosynthetic traits of 14 rice cultivars. Plants were grown under full light with 24 MJ m⁻² day⁻¹ , and both shading treatments received the same daily light integral. On average, continuous shading reduced grain yield by 28 % and aboveground biomass by 27 %, whereas intermittent shading resulted in greater decreases, by 32 % and 31 %, respectively. Yield losses were mainly attributed to reduced tillering and to a lesser extent to 1000-kernel weight. Growth reduction was sub-proportional to light resources, indicating increased incident radiation use efficiency under shading. However, this increase was less pronounced under intermittent shading, chiefly attributable to the curvi-linear response of photosynthesis to light. Furthermore, a decrease in the maximum electron transport rate under intermittent shading conditions suggested reduced photosynthetic capacity as well. Despite substantial variation among cultivars in morphology and photosynthetic parameters under full light, none of these traits predicted differential responses to shading regimes. These findings highlight that diurnal light distribution strongly influences crop performance, beyond the effects of mean light reduction. Consideration of intermittent shading is thus crucial for understanding and modeling plant responses in multilayered systems such as agrivoltaics, intercropping, and agroforestry. • Intermittent shading reduced rice yield and biomass more than constant shading. • Yield losses were mainly due to reduction in tillering, followed by kernel weight. • Incident radiation use efficiency rose under shade, less so with intermittent shading. • Non-linear light response explained lower assimilation with intermittent shade. • Cultivars differed slightly, yet overall responded similarly to intermittent shading.