Changes of rice canopy structure under global dimming

Global dimming reduces incident radiation, and thus affects rice yield. Canopy structure is closely related to light interception, internal light distribution, photosynthesis and radiation use efficiency (RUE). However, less attention is paid to the effects of global dimming on rice canopy structure. Whether weak light leads to poor canopy structure and thus affects light distribution and RUE, thereby reducing dry matter accumulation and grain yield remains unknown. The objectives of this study were to explore the effects of global dimming on canopy structure, and its relationships with canopy light distribution and RUE under artificially simulated weak light in hybrid rice. Field experiments with two rice hybrids (Y-liangyou900, YLY900; Chuanyou6203, CY6203) were conducted under no shading (CK), 40 % shading at booting stage (S) and 40 % shading at grain-filling stage (SS) in 2021 and 2022. The effects of shading on the growth characteristics and yield of rice varied with different varieties. Shading at booting stage resulted in larger basal, opening and drooping angles of the top three leaves of both varieties. This rise in leaf angles increased the light extinction coefficient (KL) of YLY900, but it had no significant effect on CY6203. Shading significantly reduced RUE during the total growth period, with reductions of 24.3 % and 16.8 % under S, and 11.1 % and 8.9 % under SS for YLY900 and CY6203 in two years, respectively. The total dry weight of YLY900 under S and SS was 34.6 % and 22.8 % lower than that under CK in both years, accordingly, the total dry weight of CY6203 was 27.0 % and 21.6 % lower, respectively. Ultimately, shading resulted in a significant decrease in grain yield compared with CK, and the effect of S on yield was greater than that of SS because of the significantly lower spikelet differentiation under S. In terms of varieties, shading had a greater effect on canopy structure, light distribution and RUE of YLY900 than that of CY6203, which explained yield advantage of CY6203 over YLY900 under shading. Shading increased leaf angles of the top three leaves and caused a draped canopy structure. This change affected the canopy light distribution and RUE. Therefore, the varieties with slightly draped upper leaves might be better able to adapt to the global dimming and reduce yield loss. Understanding the changes of canopy structure, light distribution and RUE under shading were highly significant for the breeding and cultivation of climat