Effect Of Light Quality On Growth And Physiological Characteristics Of Pakchoi

In order to investigate the effect of light quality on regulation mechanism of pakchoi,we designed five different combinations of light quality(light recipe)using light-emitting diode(LED)as light source: white(W,control),white/ blue ratio= 4:1(WB),white/ red ratio= 4:1(WR),white/ red/ blue ratio= 3:1:1(WRB),white/ green ratio= 4:1(WG),the total photosynthetic photon flux density(PPFD)was the same in each light treatment(about 250 μmol·m-2·s-1).The cultivar ‘Youguan 3’(heat-resistant)and ‘Wan Chou Lv Yang’(cold-resistant)were used as experimental materials,and the effects of different light quality and ratio on growth and photosynthesis were studied.In addition,tunnels were covered by colorless,purple,blue,red and green color films respectively,and the colorless film was control;the light intensity was regulated at the same level by covering the plastic net,and we studied the effects of different color agricultural plastic films on growth,yield and quality of pakchoi.Finally,on this basis,the effects of different transmittance of red films on growth,yield and quality of pakchoi were studied.The main results as follows:1.The plant height increased significantly by 17.9% and 7.5% under WRB and WR respectively;the contents of chlorophyll a,chlorophyll b and total chlorophyll were highest under WRB treatment,while were lowest under W treatment;net photosynthetic rate(Pn)and RuBP carboxylase activity were highest under WRB treatment;WR,WB and WRB increased stomatal conductance(Gs)by 9.7%,47.4% and 31.6% respectively compared to W;WRB increased Fv’/Fm’、ΦPSII、qP、ETR and Rfd of pakchoi leaves.2.The contents of total sugar,reducing suger,sucrose and starch in WRB treatment were significantly higher than control.Compared to W,WRB,WR and WB increased sucrose phosphate synthase(SPS)activity by 46.9%,22.3% and 14.7% respectively.The synthetase synthetase(SS)activity of WB and WRB treatments were lower than that of control.The contents of total nitrogen were lowest under WG treatment,while other treatments showed no significant differences compared to W.The content of protein nitrogen and activity of nitrate reductase(NR),glutaminase(GS),glutamate synthase(GOGAT)and glutamate dehydrogenase(GDH)were highest under WRB treatment,and the expression of genes related to nitrogen metabolism enzyme were up-regulated compared to control.In conclusion,supplement red and blue light simultaneously to white light couldenhance the activity of PSII reaction center,improve the photosynthetic performance,and increase dry matter accumulation and light energy use efficiency.Therefore,red and blue light can be used simultaneously as supplementary light for pakchoi cultivation to improve photosynthetic performance and yield,and white:red:blue = 3:1:1(WRB)was suitable light recipe.3.The red film increased pigments content and improved the photosynthetic performance and growth of ‘Wan Chou Lv Yang’ and ‘Youguan 3’.Compared to control,the yield of ‘Wan Chou Lv Yang’ and ‘Youguan 3’ were increased by 7.6% and 10.2% respectively.Besides,the red film improved the quality of two kinds of pakchoi.Therefore,the red film is more suitable for the growth of pakchoi.4.The red film with 45% transmittance decreased temperature and increased solar radiation,humidity and the yield and quality of pakchoi,which indicated that the 45% transmittance of red film was more suitable for the pakchoi.