Mechanism Of Greenhouse Melon's Adaption To Brackish Water Irrigation And Risk Analysis Of Salt Damage

In order to evaluate the effects of brackish water irrigation on musk melon cultivated on sand condition. Different concentrations brackish water was supplied at four different developmental stages in this experiment. The trail was conducted by the two factors and four levels random block design. The adaptability of musk melon of different stages to various concentrations of irrigation water were studied from the following aspects: the growth and development of the plant,the Membrane Lipid Peroxidation and the activity of Protective Enzyme,yield and quality of the plants,absorption,distribution and transportation of the salt ions under experimental conditions. Meanwhile,the method of risk analysis was used to evaluate the risks of musk melon cultivated in the greenhouse irrigated with brackish water. The main results were as follows.1. The growth and development rules of melon under brackish water irrigationThe study of the plant height,leave number,leaf area,fruit set node,percentage of withered leaves and the accumulation and distribution of dry matter proved that the most significant external effects of brackish water irrigation was the constriction of growth.(1) Effect of brackish water irrigation on the plant height and the establishment of the model of the plant heightCompared with CK,the height of the plant irrigated with brackish was decreased and the speed with which they dropped was correlated with the concentration of the irrigation water. There was a dramatically decrease of the treatment which was supplied with brackish water constantly and which is not recoverable. Heights of the plants supplied with brackish water from the straw period and flor-fruit period separately suffered a slight decrease and recovered during the later developmental stages. Brackish water irrigation indicated no effects when supplied from the fruitage due to tipping. The model of plant height obtained under experimental condition is PHd=PH0+LR0×TUd×DWSTR(S).(2) Effects of brackish water irrigation on the development of leavesBrackish water supplied from the flor-fruit period and the fruitage exert few effects on the numbers of the leaves,while the numbers of the leaves were less than CK when the plants started to be supplied with brackish in straw period and steadily treatment. The decrease of the former one was probably caused by the constriction of the growing speed,which is recoverable. However,the drop of the latter one was likely due to the blunt with blossom caused by high concentration and constant brackish water irrigation,which is irrecoverable.The former one belongs to recoverable strain and the latter to irrecoverable strain. Brackish water irrigation leads to the decrease of leaf area,the leaf area of the plants decrease when supplied with brackish water from the straw period and the fruitage,however,the biomass of the leaves increased,which indicated the thickness of the leaves increased this can minimize evaporation in order to adapt to the water stress due to brackish water treatment.All but the treatment which starts to be irrigated with brackish water from the straw period showed a higher percentage of withered leaves than the CK. This not only the result of nutrition competition but an adaptable response to over absorbed Na+,Cl-.(3) Effects of brackish water irrigation on the fruit growth and developmentIrrigated with brackish water from the flor-fruit period can cause abortion and raise of fruit set node while for the straw period and steady treatment the fruit set node was lowered due to brackish water irrigation thus the whole development stage was shortened. Model of yield reduction under experimental condition is:Ya=[1-(SC-SCthreshold) b/100]Ym,Models of yield reduction of the straw period,flor-fruit,fruitage and steady treatment are:Ya_{straw period} =[1-(SC-7) 5. 00/100]Ym (R=0.8340)Ya_flor-fruit =[1-(SC-3) 5.67/100]Ym (R=0.9442)Ya_fruitage =[1-(SC-3) 5.55/100]Ym (R=0.9808)Ya_{steady treatment} =[1-(SC-3) 6.54/100]Ym (R=0.9794)2. The response of membrane lipid and protective enzymes in melon leaves to brackish water irrigation during various developmental stagesThe result indicates that the average content of MDA increases as the concentration of the irrigation water increased and the time of treatment prolonged and it correlates with the starting time of treatment. Compare to the treatment began at the straw period; the average content of MDA is significantly lower than that began at the fruitage(P<0.05). Under the steadily treatment,MIP increased steadily and higher than the CK in all concentrations. For the flor-fruit period and fruitage treatments,MIP stayed constantly below CK before the concentration reached about 5 g·L-1 and after that became higher than CK. Whereas the MIP of straw period reached its bottom in the same concentration and exceed CK when the concentration climbed to approximately 7 g·L-1,which probably suggested that the maximum concentration of brackish water varied from different developmental stages of the plant.There exists no regularity of the activities of protective enzyme which can not indicate the degree the plants adapted to the brackish water. The changing regularity of MDA content and MIP demonstrates an excellent corresponding relationship with the plants and which can be used as an reference indicator to assess the adaptability of musk melon to brackish water irrigation to some degree.3. The establishment of brackish water irrigation schedule based on its effect on fruit yield and quality of melonThough the determination of the yield and the quality of the musk melon irrigated with brackish water we found that concentration of the water and the time of its supply has different effects on the plants. Firstly,watered with brackish water from the straw period with the concentration no higher than 7 g·L-1 has no effects on the yield compared with CK and the quality indicators were not influenced as well except Vc content. Secondly,irrigated with brackish water from the flor-fruit period and the steady treatment showed a significantly decrease on yield compared with CK when the concentration of irrigation water is higher than 3 g·L-1. All the indicators evaluate the fruit quality decreased while that for organic acid content increased. Thirdly,when supplied with brackish water the concentration of which is higher than 3 g·L-1 during the fruitage,the yield decreased significantly but all the quality indicators improved.Based on the study the following irrigation schedule can be concluded: brackish water no higher than 7 g·L-1,fresh water and brackish water no higher than 3 g·L-1 can be used for irrigation during the straw period,flor-fruit period and fruitage respectively which have no effects on yield and could also help to improve the quality of the fruit.4. The dynamic change of salty ions in different organs of melon response to brackish water irrigation during various developmental stagesThe content of Na+ in the plant indicates the concentration effect,while as the time of supply of brackish water prolonged the content of Na+ demonstrates the time effect. The content of Na+ in the leaves lower than that of stems and roots due to the selectivity transport illustrated the leaves'ability of Na+ exclusion which protected the plants from the injury of salt stress.The content of Cl- in the plant showed a higher level at the very beginning after being treated and maintained at a higher level with time prolonged,and indicated no discrepancy among different organs. The result explains it is easier for Cl- than Na+ to move between different organs and musk melon belongs to those have the ability of Na+ exclusion and do not have ability of Cl- exclusion .The effect of brackish water irrigation on K+ was that the content of K+ in the stems and leaves increased in the beginning and decreased dramatically after that. The content of K+ in the leaves suffered a steep decline while that in the roots showed no obvious change. This phenomenon showed that under a certain range of salt stress plants were able to maintain the normal metabolism by absorbing K+ using leaves,but the a long time brackish water irrigation can make the psychological activity of the stems and roots declined very quickly. Therefore,compared with long time and low concentration brackish water,short time and high concentration brackish water were better when used for irrigation.The effect of brackish water irrigation on the distribution of Ca+ is not obvious and which stood at a higher level in all treatments which illustrated that the Ca2+ of the membrane were not substituted by Na+ and remained its integrity. However,long time brackish water irrigation made the Ca2+ content significantly higher than that of the CK suggested that the Ca2+ content was not able to decreased to a lower level and were likely to make damage to the leaves.We found from the study that the increase of the concentration of the irrigation water could reduce the K+/Na+,Ca2+/Na+,Cl-/Na+ ratios. The main reason for the decline of K+/Na+ and Ca2+/Na+ was the accumulation of great amount of Na+,not for the Ca2+ and K+ were substituted by Na+. The reason why the content of K+ can maintained at a normal level is mainly because the higher selectivity of the membrane,however,such kind of adaptability declined as the time of salt-stress prolonged.The result of this experiment indicated that the most obvious effects of brackish water irrigation were the constriction of growth. Effects on the growth and development of the melon were mainly because the balance between different irons was damaged not for the absorption decline of other irons. The adaptability of musk melon under brackish water irrigation condition was featured by absorption increase of K+ and Na+ exclusion of the leaves. The content of different irons and ratios between the irons varied with the concentration of the irrigation water and the development stages,among which,the ability of osmotic adjustment changed as the concentration of the brackish water and time of the treatment.5. Establishment risk assessment model for analysis of the salt damage of melon with brackish water irrigationAn analytic hierarchy process was designed to weight risk factors and these factors were classified and quantified. So an integrated assessment method was applied to calculate the probability of the risk and the sequence of the weight of risk factors is a clue for risk manages to decrease the risk. Then an initial model for risk evaluation of salt damage of melon under brackish water irrigation condition was established. The method provided a new thought for risk evaluation of brackish water irrigation applied in the greenhouse could be used as a reference for the future study.