| In maize-soybean relay strip intercropping system,during the co-growth period,soybean suffer shade environment,the morphological and physiological changes greatly and the adaptability to shade of different soybean varieties was different.After maize harvesting,soybean grown in full sunlight.Compensatory growth was observed in plant morphology,dry matter distribution,leaf structure and photosynthetic physiology,it plays an important role in the formation of soybean yield.Therefore,it is necessary to find out the response mechanism of soybean to the light recovery signal after shading,and find out the key trait to determing the yield at this stage,which plays an important role in the variety breeding and selection of soybean for intercropping.In this study,136 soybean varieties were grown in simulated shade environment to investigate the changes of morphology and structure of soybean in the light recovery period,and to find the key traits causing the difference of compensation growth ability between varieties.The photosynthetic physiological differences of soybean varieties with different compensatory growth ability were compared when soybean transfered from shade to light recovery.Finally,the effects of shade and light recovery environment on key characters of compensatory growth（leaf area）were analyzed.The main research results are as follows:1.To explore the changes in morphology of soybean when transfed from shade to full light environment,we investgated morphology,biomass and it’s distribution for 136 soybean cultivars,which were planted in a simulated shade condition.Results found that:shade significantly decreased the aboveground biomass,first node diameter,leaf area,number of nodes on main stem,branch number,blade thickness,and increased biomass fraction to stem,stem lengh,LAR,SLA.After light recovery,the increase speed of stem length,LAR and SLA was slower than that under shade,the diameter for first node,leaf area,number of nodes on main stem,branch number and leaf thickness decreased slower than under shade.Correlation analysis found that yield was significantly positive related to the compensation coefficients of SPAD,leaf biomass,aboveground biomass,diameter for first node,leaf area,branch number,the hight of lowest branch at 30 days after light recovery.Principal component analysis found that the stem dry weight,leaf dry weight,total dry weight of overground and leaf area can reflect 35.59%of the original data information.The groupⅣ（10 cultivars）showed the strongest compensation growth ability and the highest yield with the highest aboveground biomass,leaf area,branch number and number of nodes on main stem,lowest stem length/aboveground dry weight and lowest stem length/leaf area.2.To compare the difference in photosynthetic between different compensatory growth ability cultivars when transferred from shade to full light.we investgated morphology,biomass,leaf traits,photosynthetic and yield for three soybean cultivars（strong:Nandou12,middle:Texuan13,weak:Jiuyuehuang）,which were planted in a field experiment.Results found that,in maize-soybean relay strip intercropping,the mean annual yield for Nandou12 and Texuan13 were 1159.6 kg hm-2 and 1131.4kg hm-2,respectively,both them significantly higher than that of Jiuyuehuang(566.9 kg hm-2).The shade period significantly decreased photosynthetic area（leaf area,leaf number,leaf size）and photosynthetic ability（SPAD,net photosynthetic rate,Rubisco content and total activity）for three soybean cultivars.After light recovery,the dry matter accumulation rate of the three soybean varieties was 2-5 times higher than that of the monoculture crop,the photosynthetic area and photosynthetic capacity could be recovered quickly,but only the ultrastructure and SPAD can returned to the monoculture level.The photosynthetic area and photosynthetic ability for Nandou12 were significantly higher than that of Jiuyuehuang.This indicated that the varieties with stronger compensatory growth ability can increase the leaf area and restore the photosynthetic capacity after light recovery,thereby increasing the interception and utilization of light energy,increasing the dry matter accumulation rate and obtaining higher final yield.3.To gain more insight into how shade affects leaflet area for soybean,we conducted a pot experiment to investigate the leaflet area,leaf anatomical structure,hormones and genes expressions related to cell proliferation and enlargement for young,middle and old leaves for Nandou12.Results found that shade treated plants showed signifcantly increase in stem length and petiole length,and decrease in stem diameters,shoot biomass and its partition to leaf also were signifcantly lower than that in full sunlight.Smaller and thinner on shade treated leaves than corresponding leaves on full sunlight plants.The changes of cell number and cell size in young leaves after shading were significantly greater than those in old leaves and cell size.Which illustrated that the decreased leaflet area caused by shade was largely attributable to cell proliferation in young leaves and both cell proliferation and enlargement in old leaves.Shade induced the expression of a set of genes related to cell proliferation and/or enlargement,but depended on the developmental stage of leaf.Shade signifcantly increased the auxin and gibberellin content,and signifcantly decreased the cytokinin content in young,middle and old leaves.Taken together,these results indicated that shade inhibited leaflet area by controlling cell proliferation and enlargement in young stage and controlling cell enlargement in old stage.Cytokinin may play important roles in this process.4.Pot experiment and field experiment were conducted to analyze the effects of light recovery on leaflet area for three soybean varieties（Nandou12,Texuan13 and Jiuyuehuang）.Pot experiment results:Compared with the full sunlight treatment,the shade mature leaves treatment significantly decreased the leaflet area,blade thickness,sponge tissue thickness,cell number and net photosynthetic rate,sugar content and cytokinin content and increased the auxin content for the new developing leaves of the three soybean varieties.Under the shade mature leaves treatment,the sugar content and cytokinin content for Nandou12 were significantly higher than that of Jiuyuehuang.Field experiment results:After light recovery,the leaflet area for new developing leaves were still significantly smaller than that of in the control.For Nandou12,there was no significantly difference in the thickness of the palisade tissue and the thickness of the sponge tissue between two treatments,while for Jiuyuehuang,the leaf thickness,palisade tissue thickness and sponge tissue thickness were significantly lower than the control.For both Nandou 12 and Jiuyuehuang,the cytokinins was still significantly lower but the starch content was significantly greater than the control.The above results indicated that the leaflet area could been decreased by shade environment,but the subsequent light recovery can’t recover the leaflet area to the control level,this indicated that the shading environment in the early stage could systematically regulate the leaflet area for the new developing leaves,even though the new developing leaves exposed to full sunlight.The cultivar with strong compensation growth ability shows more recovery in leaflet area,energy accumulation and cell division in the early stage may be the main determining factor to system regulate the leaf expansion. |
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