Abstract: 【Objective】The present work studied the effect of shading on photosynthesis and chlorophyll fluorescence characteristics, including leaf area, lamina mass per unit area, chlorophyll content, yield characters, photosynthetic and fluorescence parameters of three soybean cultivars at different growth stages, in order to support the development of maize-soybean intercropping and relay-intercropping systems in hilly and mountainous area of southern China.【Method】Three cultivars named Guixia 2, Nandou 12 and C103, whose period and total days for growth were different with each other, were studied. Soybean plants were shaded by shading nets with 50% transmittance during growth stages of emergence to full-bloom (VER2), emergence to pod-fill (VER5), and full-bloom to full-ripe (R2R8), respectively. Plants grown under natural light were used as control (CK). Leaf area, lamina mass per unit area, chlorophyll content, photosynthetic and fluorescence parameters, as well as yield characters were measured and analyzed. 【Result】 Compared to the control (CK), leaf area, chlorophyll (a+b) content and apparent quanta efficiency at the VER2 stage increased by 15.5%, 13.0% and 74.1%, respectively; lamina mass per unit area, light compensation point and maximum photosynthetic rate were decreased by 15.8%, 26.2% and 26.5%, respectively, compared to CK. Leaf area, chlorophyll (a+b) content and apparent quanta efficiency increased by 0.3%, 10.5% and 28.1%, respectively at the R2R8 stage; while lamina mass per unit area, light compensation point and maximum photosynthetic rate decreased by 10.2%, 20.3% and 12.1%, respectively, compared to CK. When soybean plants were re-illuminated at full bloom stage, maximal quantum yield of PSII was decreased by 3.0% and non-photochemical quenching was increased by 26.8%, compared to CK. When plants were re-illuminated at pod-fill stage, maximal quantum yield of PSII was decreased by 8.5% and non-photochemical quenching was increased by 40.8%, compared to CK. In addition, at VER2, VER5 and R2R8 stages for Guixia 2, yields per plant decreased by 40.8%, 48.7% and 59.2%, and 100-seed weight decreased by 23.7%, 39.3% and 26.4%, respectively, compared to CK. For Nandou 12 at these stages, yields per plant decreased by 46.7%, 54.2% and 21.2%, and 100-seed weight were decreased by 3.9%, 19.9% and 26.1%, respectively, compared to CK. For C103, yields per plant decreased by 69.8%, 74.9% and 73.9%, and 100-seed weight decreased compared to CK by 68.8%, 69.6% and 71.6%, respectively.【Conclusion】Shading to the VER2 stage had a greater impact than for R2R8 on the photosynthesis and chlorophyll fluorescence characteristics of soybean. Photosynthetic capacity of soybean leaves made some recovery from shading when re-illuminated at R2. However, high-light stress was observed for plants re-illuminated at R5. Therefore, we suggest that maize-soybean intercropping to be a more advantageous system than relay-intercropping in hilly and mountainous area of southern China, with the perspective of minimizing the negative effects of shading on soybean photosynthesis. We also suggest, it is necessary to re-illuminate the soybean plants before full-bloom stage, in order to avoid an excessively long shading duration, when making decisions about on cultivar use, sowing time, and planting technology. The effect of shading period can influence yield of soybean. Moreover, the longer the shading duration last, the more the expected yield loss.

Key words: soybean, maize, growth stages, shading, photosynthesis, chlorophyll fluorescence