Reseach Of The Photosynthetic Characteristis Of Soybean Seeding Under Different Shading

Simulating the field maize/soybean relay-cropping pattern, we used "Nandou 12" and "Guixia 3" to analyze changes of morphological and physiological properties, photosynthetic characters, chlorophyll fluorescence characteristics, Rubisco activities and contents and gene expression in different growth periods of shading and recovery under seven shading treatments:no shading (CK), partial shading (30%,50%,70%) and full shading (30%,50%,70%). The main results are as follows:1. The morphology and physiology of soybean seedlings had great changes under different shading treatments. Shading enhanced the plant height, first branch length and leaf area of soybean seedings and reduced stem diameter and specific leaf weight. Each index at different treatments had significant differences. As the shading degree increased, the chlorophyll content of the seedling leaves increased and the chlorophyll a/b value decreased. Each different treatment had significant differences. Nandou 12 had smaller changes than Guixia 3 in each morphological and physiological index and had a higher chlorophyll b content and a lower chlorophyll a/b value.2. As shading degree increased, the initial fluorescence intensity (Fo) increased; the net photosynthetic rate (Pn), PS Ⅱ Maximum photochemical efficiency (Fv/Fm), PS Ⅱ actual photochemical efficiency (ΦPS Ⅱ) and photochemical fluorescence quenching coefficient (qP) firstly increased and then decreased; stomatal conductance(Gs) and transpiration rate(Tr) decreased; intercellular CO2 concentration and chlorophyll fluorescence Non-photochemical quenching coefficient (NPQ) firstly decreased and then increased. The photosynthetic and fluorescence parameters of the two soybean cultivars had small differences under moderate shading degree. However, Nandou 12 had a stronger adaptive capacity to high shading degree than Guixia 3. Nandou 12 protect the photosynthetic mechanism from destruction by increasing NPQ to dissipate excess light energy, while Guixia 3 couldn’t dissipate excess light energy in time and led to PS Ⅱ reaction center damage, which was the main reason of photosynthetic rate decrease.3. Shading had a different impact on Rubisco activity of the two soybeans cultivars. As shading degree increased, the Rubisco initial activity and total activity firstly increased and then decreased in Nandou 12, while decreased gradually in Guixia 3, "Guixia 3" has a higher Rubisco activity in the Q3 treatment than in CK. Soluble protein content of the two soybean cultivars all firstly increased and then decreased. SDS-PAGE experiment shows the content of Rubisco kinase is the highest under B3、B5 and Q3, but each different treatment had no significant difference. Shading had a little difference to the two soybean cultivars in Rubisco content, but had a greater impact on Rubisco activity in Guixia 3 than in Nandou 12.4. The expression of rbcS and RCA genes in the two soybean cultivars differs in different shading treatments. The expression of rbcS gene was highest under the B5 treatment and second hignest under the B3 and Q3 treatments in "Nandou 12", while highest under the Q3 treatment and second highest under the CK and B3 treatment in "Guixia 3". The expression of RCA gene was highest under the Q3 and B5 treatments and second highest under the CK and B3 treatment in "Nandou 12", while highest under the Q3 treatment and second highest under the CK and B3 treatment in "Guixia 3".