Effects Of Rhizosphere Electrified Cultivation On Lettuce Growth,Quality And Tipburn Occurrence In A Plant Factory

With the rapid development of protected agriculture in China,vegetable production has basically met daily needs of citizens.Meanwhile,the demand for high-level vegetable quality has gradually increased.Therefore,protected agricultural vegetable production is required to be changed from quantity-oriented growth pattern to quality-oriented one.Thus,improving the quality of vegetable is important in the development of protected agriculture.Tipburn is a physiological disease in leafy vegetables caused by calcium deficiency,especially in protected environment.Once occur,tipburn would seriously decrease the appearance quality,taste and economic benefits of leafy vegetables.Therefore,in order to promote plant growth and decrease the occurrence of tipburn,the lettuce which is easy to occur tipburn in protected environment was chosen as the experimental material.Negative voltage was generated in the lettuce rhizosphere environment to make the lettuce plant negatively charged and form a positive electric field in the shoot growth space.The effects of different rhizosphere electrified intensity on the lettuce growth and quality were studied to explore the effects of rhizosphere electrified cultivation on lettuce growth,root absorption,Ca²⁺absorption and tipburn occurence.（1）The total light intensity was set at 200μmol/（m²·s）,R:B was 4:1.-15 k V rhizosphere voltage was set as the treatment,and the non electrified treatment was set as the control.The results showed that:the tipburn occurrence was found on the 13th day under control,while it was found on the 15th day under treatment,meanwhile,the ratio of leaves with tipburn to total leaves was reduced by 46.9%on day 20.on the 20th day,compared with those under control,lettuce shoot fresh weight and root fresh weight under treatment increased by 6.3%and 30.9%,respectively,and shoot dry weight and root dry wight under increased by 17.2%and 22.4%respectively.On the 20th day,the stomatal conductance,transpiration rate and intercellular carbon dioxide concentration of lettuce under treatment increased by 46.2%,49.0%and5.2%respectively,compared with those under control.The accumulation of photosynthetic biomass of lettuce was also increased,but the effect on photosynthetic pigment was not significant.Therefore,electrified rhizosphere cultivation can increase the biomass of lettuce and alleviate tipburn occurrence.（2）The total light intensity is 200μmol/（m²·s）,R:B was 4:1.In order to explore the effects of rhizosphere electrified cultivation on Ca²⁺absorption,transport and heat exchange in lettuce,-15 k V rhizosphere voltage was set as the treatment,and the non electrified treatment was set as the control.The results showed that:on the 10th day,the root activity and Ca²⁺absorption capacity under treatment were increased by 133.3%and 108.9%respectively,compared with those under control;on the 20th day,the total root absorption area and root activity under treatment were increased by 18.7%and 71.4%respectively,compared with those of control.There was no significant effect of treatment on the active root absorption area;on the 20th day,the latent heat flux under treatment under light and dark stages were6%and 35.6%higher than that of control,and the stomatal resistance of lettuce leaves under treatment decreased.Therefore,rhizosphere electrified cultivation can promote the absorption and transportation of Ca²⁺by increasing transpiration and reducing stomatal resistance.（3）The total light intensity is 200μmol/（m²·s）,and the light source is white LED.-10 k V,-15 k V and-20 k V rhizosphere electrified voltage were set as treatments,which were recorded as T10,T15 and T20,respectively,and non electrified treatment was recorded as CK.The results showed that:compared with that under CK,lettuce shoot fresh weight under T10 and T15 increased by 56.7%and 12.4%respectively.The calcium content in new leaves under T20 increased by 9.6%,and the ratio of leaves with tipburn to total leaves was reduced by 39.9%.The nutritional qualities of lettuce were different under different treatments.The soluble protein content under T10 and T15 increased by 29.6%and 25.9%,the soluble sugar content under T10 increased by 23.8%.The total nitrogen content of lettuce leaves under T10,T15 and T20 increased by 47.6%,25.2%and 21.2%respectively,the calcium content in old leaves increased by 47.6%,25.2%and 21.2%,and there was no significant effect of three treatments on the nitrate content of lettuce.In conclusion,in the plant factory with intergral environmental control and R:B ratio of 4:1,-15 k V rhizosphere electrified cultivation could significantly improve lettuce growth,and effectively alleviate tipburn occurrence.In the plant factory with intergral environmental control and white LED,different rhizosphere electrified intensity showed different effects on lettuce growth and quality.T10 and T15treatments could increase the yield and soluble protein of lettuce.T20 treatment could promote the accumulation of calcium in new leaves of lettuce by increasing root activity,thus reducing the incidence of tipburn and improving the appearance quality of lettuce.Therefore,the suitable rhizosphere power intensity can be selected according to different production needs.T10 and T15 treatments were helpful to improve the fresh weight of lettuce shoot,while T20 treatment was helpful to reduce the occurrence of lettuce tipburn.