Effect of shading on photosynthetic and chlorophyll fluorescence characteristics of soybean

This study investigated the photosynthetic response of soybean seedlings under different shading conditions.Simulating the field maize/soybean relay-cropping pattern,two soybean cultivars,Nandou 12andGuixia 3,were utilized to analyze changes in the pigment content,photosynthetic rate and chlorophyll fluorescence parameters at different growth stages under shading and during light recovery stages.Five shading treatments were set;no shading,30% partial shading,50% partial shading,70% partial shading and 50%full shading.Shading increased the pigment content and original fluorescence intensity while the chlorophyll a/b ratio decreased.Photosynthetic rate,maximal photochemical efficiency,photochemical efficiency and photochemical quenching initially increased and then decreased,while non-photochemical quenching initially decreased before increasing.The soybean seedlings grew strongly under 50% partial shading but growth was poor under50%full shading.Shading had a marked effect on seedlings at the four-trifoliolate leaf stage;when shaded,seedlings accommodated the weak light environment by changing the pigment composition or promoting photosynthetic electron transport.Nandou 12showed better shade tolerance and higher photo chemical efficiency than Guixia 3.Guixia 3was unable to dissipate excess light energy under light recovery resulting in severe damage to the photosynthetic system.