Effects Of Shading And Restoration Light Intensity On Photosynthetic Characteristics, Nitrogen Metabolism, Yield And Quality In Various Varieties Relay Cropping Soybean

This experiment was carried out to study the effects of shading on relay-cropping soybean's photosynthetic Characteristics,nitrogen metabolism,yield and seed quality,and the effects of restoration light intensity on fluorescent characteristics and nitrogen metabolism by using various varieties of late-maturing soybeans seedling in wheat/maize/soybean cropping system. (shade tolerant 'Gongxuan 1','Nandou 12' and shade susceptible 'Nan dongkang 022-2','Gong qiudou 494-1').The main results showed as follows:1.Under relay-cropping system the total chlorophyâ…¡content of the four cultivars increased; while,the ratios of Chla/b and the content of carotenoids decreased.From the response data of Chlorophyâ…¡fluorescence,it was seen that with the decreasing of light intensity,there was a more increased in the minimal fluorescence(Fo) and the actual photochemical efficiency of PSâ…¡in the light(ΦPSâ…¡);and it indicated that soybean grow under Relay-cropping had lower maximal photochemical efficiency of PSâ…¡in the dark(Fv/Fm) as compared with those grown under monoculture.The net photosynthesis rate(Pn),stomatal conductance(Gs),stomata limitation(Ls) and transpiration rate(Tr) decreased;ratio of intercellular to ambient CO₂ concentration and water use efficiency increased.Poor light resulted in lower weight of dry matter accumulation in Maize/Soybean relay-cropping.Soybean with lower Pn decreasing higher Chlb,the molecular composition proportion of Car,Fo and Fv/Fm may possess potential low light-tolerance.2.The plants grown under relay-cropping had higher total nitrgen,relatively lower total carbon,thus C/N decreased.And more C/N was distributed into stem system compared with leafs.The nitrate nitrogen content increased,the activities of nitrate reductase(NR) and glufamine synthetase(GS) in functional leaves of soybean were significantly increased.The low light inhibited soluble protein expression of functional leaves,however,the amino acid contents slightly increased in leaves.These effects occurred significant differences among various varieties with those had different shade tolerance.More lower C/N and relative higher nitrate nitrogen content and amino acid contents were found in plants of 'Gongxuan 1','Nandou 12' which have relatively better shade tolerantion,and the decreased extent of soluble protein content were smaller than shade susceptible. 3.Exposure of relay-cropping soybean to natural light intensity,the decreased degree of Fo,Fv/Fm and the increased extent ofΦPSâ…¡reduced significantly;total carbon were still lower than monoculture,but decreased degree reduced,total nitrgen turned to decrease,thus causing decreased degree of C/N reduced;after restoration light intensity 15 days,the nitrate nitrogen and amino acid contents of stems and leaves had a great change,which turned to decrease.In which the amino acid contents of 'Gongxuan 1','Nandou 12' respectively decreased by 7.35%,7.01%,while 'Nan dongkang 022-2','Gong qiudou 494-1' respectively decreased by 14.57%,13.67%;the dry matter accumulation enhanced rapidly,and reduced significantly with monoculture.When transfering from shading to relative strong light,various varieties soybean which had different shade-tolerant had obvious differences,the recovery degree of 'Gongxuan 1','Nandou 12' were higher than 'Nan dongkang 022-2','Gong qiudou 494-1',shade tolerant varieties'('Gongxuan 1','Nandou 12') Fo,Fv/Fm and C/N manifested as over compensation phenomenon.4.There was no significant change of soybeans' seed number per pod under relay-cropping system,and the main factor affecting it was specie,that was,the genetic and physiological differences.The pod number per plant,100-seed weight of four various varieties was significantly lower than monoculture soybean,consequently reduced the final yield of relay-cropping soybean.Shade tolerant soybean 'Gongxuan 1','Nandou 12' with higher pod number per plant,100-seed weight,seed number per pod and yield,in which the yield of 'Gongxuan 1','Nandou 12' decreased by 17.71%,19.74%,'Nan dongkang 022-2','Gong qiudou 494-1' decreased by 38.43%,37.49%.The grain protein,'total protein and oil' were higher than monoculture soybean,and crude fat lower than that of monoculture treatment,shade tolerant soybean 'Gongxuan 1','Nandou 12' were prone to the accumulation of protein,crude fat and 'total protein and oil'.