| This research was conducted in pot and field,two soybean varieties was used as materials:Nandou 12(shade tolerant)and Jiuyuehuang(shade intolerant).We mearured the morphological characteristics,dry mass accumulation,leaf anatomical structure,photosynthetic traits,autioxidant enzyme activities,MDA content and osmotic adjustment substances of soybean in shade period and subsequent light recovery period in different shade degree treatments,,so as to discuss the influence of shade and light recovery on growth of soybean and to breed tolerant soybean variety for interplanting,thereby providing a theory reference frame for cultivating interplanted soybeans with high yield.1.In the study,it wass found that during the shading period,the stem diameter,biomass,node number of main stem and leaf area decreased with increase of shading extent.However,the stem length increased with increase of shading extent.The comparison between varieties shows that Nandou 12 was less influenced during the shading period.After light recovery,the stem diameter,biomass and leaf area of the two varieties were all recoveredwith different varying degrees,and the lower the shading extent in early period was,the higher the recovery capacity was.Both two varieties showed a trend of first slowly increasing then rapidly increasing after light recovery,while stem length increased slowly.On August 23,the stem length for NS 1(30%shading of Nandou 12),NS2(50%shading of Nandou 12)and NS3(70%shading of Nandou 12)were respectively 108.94%,120.81%and 148.69%of NSO(Full sunlight of Nandou 12),and the stem length for JS1(30%shading of Jiuyuehuang),JS2(50%shading of Jiuyuehuang)and JS3(70%shading of Jiuyuehuang)were respectively 167.38%,201.56%and 216.21%of that of JSO(Full sunlight of Jiuyuehuang).Among them,the above traits of Nandou 12 react to light recovery more rapidly than those of Jiuyuehuang.2.In the study,it wass found that the shading significantly reduced SPAD value of leaf.With increase of shading extent,the SPAD value decreased,and the tolerant soybean Nandou 12 has higher SPAD value than Jiuyuehuang.Besides,with increase of shading extent,the more decreased extent of leaf thickness,thickness of palisade tissue and thickness of sponge tissue.However,the decrease rate of palisade tissue in tolerant soybean Nandou 12 was lower than that of Jiuyuehuang-the intolerant soybean,which plays the major role of photosynthesis.During the shading period,the leaf thickness for tolerant soybean Nandou 12 subjected to shading treatments of S1,S2 and S3 was 87.52%,65.73%and 60.67%of those for control group,respectively.While the leaf thickness of intolerant soybean Jiuyuehuang was 72.29%,67.05%and 46.89%of that of control group,respectively.After light recovery,the SPAD values for both varieties could recover to control level,yet Nandou 12 had shorter recovery time.The leaf thickness,thickness of palisade tissue and thickness of sponge tissue for the two varieties was also gradually and nearly to control levelsafter light was recovered,and the recovery extent lowered with rise of shading extent.Among them,the leaf thickness of NS 1,NS2 and NS3 was recovered to 91.96%,82.24%and 77.27%of that of control,while that for JS1,JS2 and JS3 was recovered to 88.71%,78.47%and 68.81%.The comparison between varieties showed that the recovery extent of tolerant soybean Nandou 12 subjected to each treatment after lightrecovery was greater than that of intolerant soybean Jiuyuehuang.3.This research found that shading significantly reduced the net photosynthetic rate of soybean,compared to control,the net photosynthetic rates of Nandou 12 subjected to shading treatments of S1,S2 and S3 were decreased by 8.97%,17.67%and 41.48%.While that for Jiuyuehuang subjected to shading treatments of S1,S2 and S3 decreased by 13.19%,21.75%and 40.02%.The stomatal conductance and transpiration rate of the two varieties had the same change trend with that of net photosynthetic rate,and influence increased with increase of shading intensity.While the intercellular CO2 concentration showed the opposite trend,which indicated that stomata was not the main reason to reduce photosynthetic capacity in shade,the net photosynthetic rate decreasd with increase of shading extent.After light recovery,the soybean was still influenced by non-stomata factors.However,the photosynthetic rate indices of the two varieties were all recovered gradually.The lower the shading extent in early shade period was,the higher the recovery extent was.Net photosynthetic rates of tolerant soybean Nandou 12 in shading and light recovery were all higher than those of that in intolerant soybean Jiuyuehuang.On August 23,the net photosynthetic rates of primary leaves,reciprocal second and reciprocal third leaves for NI were 3.77%,32.44%and 13.10%higher than those for JI.The comparison between leaf positions showed that the primary leaf was recovered to control level earlier than the reciprocal second and reciprocal third leaves.4.In the present study,in shade period,the content of MDA,SOD and POD were significantly increased,while the content of soluble protein and soluble sugar dropped dramatically.After light recovery,MDA showed decrease after first rising while the content of soluble protein and soluble sugar all increae to a certain extent.Third week after light recovery,the content of soluble protein for Nandou 12 subjected to treatments of NS1,NS2 and NS3 was 42.70%,29.92%and 35.89%higher than those of control,respectively.While for Jiuyuehuang,only JS2 were significantly higher than those of the control.The comparative analysis on different leaf positions showed that the tertiary leaf has stronger resistance to oxidation.In shading period and light recovery period,because of the higher activity of internal SOD and POD andhighercontent of soluble protein and content of soluble sugar,Nandou 12 showed a stronger light adaptation by enhancing the cleaning capacity of cells forH2O2,which mitigates injury of light stress to cells. |
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