Phosphate fertilizers increase CO assimilation and yield of soybean in a shaded environment.

Two light treatments [ambient sunlight (L1) during the entire growth period and 40% shade (L2) from 40 d after sowing until 24 d after flowering] and two phosphate fertilizer treatments [no phosphate fertilizer application (P0) and a conventional phosphate fertilizer application (P1)] were used to determine how phosphate fertilizer regulates soybean [ (L.) Merr.] photosynthesis under shading. We showed that phosphorus significantly increased chlorophyll content and grain yield under shading. The light-saturated net photosynthetic rate, apparent quantum yield, maximum electron transport rate, and maximum Rubisco carboxylation rate in P1 under L2 significantly increased. Moreover, phosphate fertilizer significantly improved the electron transfer and PSII reaction center performance under shading. Therefore, phosphate fertilizer increases low light-utilization efficiency by improving PSII performance, promoting ribulose-1,5-bisphosphate regeneration, ensuring a source of carboxylate substrates, and coordinating the balance between photochemical reaction and Calvin cycle under shading.