| Previous studies on NaCl have mostly focused on the field of salt stress.When high concentrations of NaCl(50～300 mmol·L-1)are added to the rhizosphere nutrient solution,plants will suffer from salt damage.However,it has been found that the application of low concentrations of NaCl(1～5 mmol·L-1)in the rhizosphere nutrient solution can promote the growth,biomass,and nutrient content of tobacco,tomato,amaranth,non-heading Chinese Cabbage,sorghum,wheat,and corn.In the modern intensive seedling cultivation industry of cucumbers,most of the cultivation is based on the plug substrate,and the method of hydroponics is very few,which makes it difficult to apply the research results of the beneficial effects of rhizosphere nutrient solution to the growth of low-concentration NaCl in actual production.Therefore,this study changed the NaCl treatment method from"rhizosphere nutrient solution" in the literature to "leaf application".As everyone knows,the environment of nursery facilities presents the characteristics of daily dynamic changes.Cucumber seedlings are mostly in natural dynamic conditions of suitable temperature-sub-optimal temperature-occasionally high and low temperature.In preliminary experiments,we found that in the daily dynamic environment of the facility,factors such as the period of NaCl leaf application(early morning and evening)and the facility management temperature will affect the strength of the beneficial effects of leaf application of NaCl.Aiming at the diurnal dynamics of the facility microenvironment and the normalization of suboptimal temperature in the modern intensive cultivation of cucumber seedlings,in order to explore the beneficial effects of low-concentration NaCl on the growth of cucumber seedlings in the facility’s daily dynamic environment,this study was carried out in a solar greenhouse on the one hand.Carry out the small-environment temperature adjustment mode treatment of the plastic film arch shed(Experiment I,the formation of medium-low temperature L zone and medium-high temperature H zone),on the other hand,set the leaf application period treatment in the solar greenhouse(Experiment Ⅱ,spraying at 8:00-8:30 in the morning)(M zone)and 18:00-18:30 at the end of the day(L zone)),observe the concentration of NaCl applied to the leaves(0(L0 and H0),5(L5 and H5),10(L10 and H10)and 15 mmol·L-1(L15 and H15);0(M0 and E0),5(M5 and E5),10(M10 and E10)and 15 mmol·L-1(M15 and E15))have an effect on the growth,photosynthesis,and Material accumulation,root growth,and the influence of Na and Cl absorption,exploring the physiological beneficial effect mechanism of NaCl leaf application in the daily dynamic environment of the facility or under adverse conditions,and clarifying the optimal concentration of leaf application of NaCl in the agronomic management period and the temperature adjustment mode of the small environment of the facility,in order to further enrich the cucumber seedlings cultivation technology provides practical basis.1、In the facility temperature regulation mode and different time period treatments,the 10 mmol·L-1 NaCl treatment had a better promotion effect on the dry matter quality and water content of the plants.In L zone and H zone where the temperature is adjusted in the facility,the seedlings start from 2 cotyledons and 1 heart,and carry out continuous 21 d leaf application of NaCl in the evening,the dry matter of cucumber seedlings increased by 50.2%(L10)and 23.3%(H10),and the plant water content increased by 52.0%(L10)and 11.1%(H10),respectively.During the M and E periods of leaf application of NaCl,start with 2 cotyledons and 1 heart,and conduct continuous leaf application of NaCl for 17 d in the early morning and at the end of the day,the dry matter of cucumber seedlings increased by 55.3%(M10)and 33.6%(E10),and the plant water content increased by 43.8%(M10)and 31.0%(E10),respectively.2、Leaf application of NaCl can significantly promote the leaf area expansion of cucumber seedlings,and the effect of 10 mmol·L-1 NaCl is better.In zone L and zone H,the leaf area of cucumber seedlings increased by 30.4%(L10)and 15.7%(H10)compared with the control,respectively;under the treatments of period M and E,the leaf area of cucumber seedlings increased by 33.7%(M10)and 31.9%(E10)compared with the control,respectively.3、Leaf application of NaCl can promote the transfer and distribution of dry matter from leaves to stems and roots.The normalized strong seedling index(SI)of cucumber seedlings increased by 24.2%(L5)and 12.0%(H10)in the L and H areas compared with the control,respectively,and the M and E periods increased by 13.9%(M10)and 7.2%(E10)compared with the control,respectively.4、Leaf application of NaCl can promote the increase of the accumulation of nutrients in cucumber seedlings under the temperature regulation mode of the facility and the treatment at different time periods.Among them,the soluble sugar content increased the most under L10 and M10 treatments,which were 32.7%and 32.0%higher than the control,respectively;The free amino acid content increased the most under H10 and E10 treatments,which were 58.6%and 45.4%higher than the control,respectively.Leaf application of NaCl during L zone and M period promoted cucumber seedlings to accumulate more soluble sugars,while H zone and E period would accumulate more free amino acids.5、Leaf application of 5～10 mmol·L-1 NaCl significantly promoted the net photosynthetic rate(Pn)and stomatal conductance(gs)of cucumber seedlings.The net photosynthetic rate(Pn)of cucumber seedlings in the L and H areas increased by 55.0%(L5)and 49.3%(H10)compared with the control,respectively.The M and E periods increased by 15.5%(M10)and 22.9%(E10),respectively.6、Under M and E period treatments,leaf application of NaCl had a promoting effect on the growth of cucumber seedling roots.The volume and root tip number of cucumber roots under M10 treatment increased by 28.7%,14.9%,compared with the control,respectively.E10 and E15 treatments have an average increase of 21.5%,19.5%compared with the control,respectively.7、When NaCl was applied to the leaves during the two periods of M and E,the concentration of Na(except the root)of the whole cucumber seedlings increased by 6.6%(M10)and 5.5%(E10),and the concentration of Cl increased by 97.8%(M10)and 56.6%(E10)compared with the control,respectively.The absorption of Cl in plants was higher than that of Na.Na showed the characteristics of accumulation in the stem.Under the M10 treatment,the Cl showed the characteristics of retention in the leaves and the accumulation of petioles and roots,while the E10 treatment showed the characteristics of accumulation in the petioles and stems.8、In the facility temperature regulation mode,the dry matter,leaf area,Pn,water content,SI,gs and free amino acid content of cucumber seedlings are affected by the single-factor effect of temperature and NaCl concentration,while the water content,SI,gs and free amino acids of the seedlings(except the leaves)is also affected by the interactive effect of temperature and NaCl concentration;the water content,Tr and Pn of cucumber seedlings are significantly affected by two single factors of time period and NaCl concentration under different time treatments.While Cl concentration and dry weight are significantly affected by the time period and NaCl 2 single factors and the interactive effect of time period and NaCl concentration.In summary,the application of low-concentration NaCl to leaves can promote dry matter accumulation and water accumulation of cucumber seedlings regardless of whether it is in the medium-low temperature(L zone)and medium-high temperature(H zone)of the facility temperature regulation mode,or under the treatments in the early morning(M period)and the end of the day(E period).However,the promotion effect of the medium and low temperature(L zone)is better than that of the medium high temperature(H zone),and the early morning(M period)is better than the end of the day(E period).The L zone(10mmol·L-1NaCl)and the M period(10～15mmol·L-1NaCl)have a greater effect on promoting dry matter accumulation,especially water accumulation,and are more conducive to the cultivation of healthy cucumber seedlings. |
