Effect And Simulation Of Low Irradiation On Growth And Quality Of Protected Cucumber

In recent years, the area of facility vegetables production china has developed rapidly. The low irradiation has become the most restrictive factor in the production of facility vegetables. The predecessors were mostly using artificial climate chest and mainly focused on the cucumber leaf photosynthesis and chlorophyll fluorescence parameters at the seedling stage.Therefore study on the effect of low irradiation on growth, fruit quality and yield of cucumber at the flowering and fruit setting stage is less.In order to study the effect of low irradiation on photosynthesis, antioxidant enzyme activity, growth characteristics and fruit quality and yield of cucumber at the flowering and fruitsetting stage,using the cucumber cultivar "Derit L108"(Cucumis sativus L. cv. Derit L108) as experimental material respectively. There are six different durations( 1d, 3d, 5d 7d, and 9d) under low irradiation(<200?mol(photon)·m-2·s-1) and four shading degrees (100%, 60%, 40%, 20%) have been designed. And on the basis of thermal effectiveness and photosynthetically active radiation (TEP) and the effect of temperature and light (LTF) method,research constructed simulation models of cucumber growth, dry matter and yield, meanwhile divided the grades of low irradiation. The main conclusions are as follows:(1)The specific leaf weight decreased, leaves become thinner under low irradiation,the net photosynthetic rate decreased,and the stronger the intensity of low irradiation, the longer the duration of low irradiation, the smaller the net photosynthetic rate. The cucumbers under 7days of low irradiation, its stomatal limitation value,net photosynthetic rate, and the photosynthetic capacity gradually returned to normal level when recovered after 9days under normal irradiation, while the cucumbers under low irradiation 7days, the net photosynthetic rate decreased by 55.2%, the stomatal limitation values increase by 44.6%, and the photosynthetic parameters of cucumber were not returned to normal level after 9 days.(2)The activities of superoxide dismutase (SOD) and superoxide dismutase(POD) in cucumber leaves were increased under sustained low irradiation, the activity of catalase (CAT) decreased, while the content of malondialdehyde(MDA)increased continuously. The stronger the intensity and longer the duration increased,the greater the increase. After returned to normal irradiation conditions, the activities of SOD, POD and content of CAT in cucumber leaves which treated less than 7days recovered to normal level quickly, the content of MDA continued to decline. The activities of SOD increased by 42.6%, and the content of MDA increased by 99.1%in cucumber leaves under low irradiation 7days compared with the control, which after 9days were still 7.8% and 60.5% higher than the control respectively. And each index of cucumber leaves which under low irradiation above 7 days were difficult to recover to normal level in a short time.(3)Compared with the control, the stem diameter, leaf area, the fresh and dry weight aboveground, fresh weight and dry weight underground were all decreased,and the specific leaf area increased; the longer the duration, the greater the decline.The height, stem diameter, leaf area per plant of cucumber increased, while the leaf area decreased gradually when return to normal irradiation.The growth rate of height,stem diameter, leaf area of cucumber under low irradiation less than 7days were recovered to normal level in a short time. The height and stem diameter of cucumbers decreased by 8.1% and 9.6% respectively compared with the control and the specific leaf area increased by 49.9%, which after 9days can still not recover to normal level.(4)The growth rate of cucumber fruit length and fruit diameter was reduced in different degrees.The water content and the content of vitamin C, anthocyanin,soluble sugar in cucumber fruits under low irradiation 9days decreased by 1.4%,54.0%,42.0% and 42.6% respectively compared with the control, while the content of organic acid increased by 32.5%. The results contribute to decrease of the nutritional quality of fruits significantly, and according to the appearance quality of cucumber fruit, low irradiation also lead to the increase of the proportion of secondary fruit of cucumber. And the longer the duration, the greater the proportion of bad fruit.The weight of cucumber fruit decreased, lead to the decreas of yield, the stronger the intensity of low irradiation, and the longer duration of low irradiation,the smaller the yield.(5) Study has introduct the stress coefficient. And the simulation accuracy of TEP model is next to LTF method, the simulation of dry matter production of cucumber was better than that of dry matter distribution index (the simulated result of the dry matter underground was the worst), and the simulation of leaf area was the most stable. The weights were determined by analytic hierarchy process and the simulation model of protected cucumber yield during flowering and fruit setting period was established. On the base of stress indexs, study had divided the grades of low irradiation into slight, moderate and heavy according to the indexs.The results can provide theoretical basis and technical support quantitative evaluation of the loss caused by low irradiation for protected cucumber.