| With the continuous development of modern agriculture in our country, the seedling cultivation in factory has become an important part of modern agriculture.The heat stress around rhizosphere during summer season is an important factor limiting the seedling growth. In order to reduce the high rhizosphere temperature during the process of seeding, two kind of water-cooled seedling beds were designed by using groundwater as a circulation medium. For Seedlings rhizosphere cooling treatment, trapezoidal metal pipe seedbed(M)use stainless steel ladder exhaust pipes as the cooling pipe, while plastic pipe seedbed(P)use PE pipe. We tested the tomato as material, studing the two kinds of water-cooled bed cooling effect and influencing on tomato seedling growth. According to the remarkable metal trapezoidal seedling bed, five different cooling time: M1(07:00-11:00)、M2(11:00-15:00)、M3(07:00-19:00)、M4(19:00-07:00)、M5(cooling all day), were set up to study the different times of the rhizosphere cooling effect on seedling growth. Finally to find the way to promote seedling growth strong.In order to explore the beneficial alleviate effect of root-zone cooling to high temperature, aiming to provide theoretical basis for the summer heat intensive seedling and technical reference.The main results were following:1. Different water-cooled seedling bed rhizosphere cooling effect on tomato seedling growthCompared with control, M seedling bed seedlings rhizosphere accumulated temperature, daily average temperature and the high temperature decreased respectively 143.83 ℃, 4.23 and 6.75℃ ℃, and the P seedling bed respectively decreased 55.35 ℃, 1.63 and 2.68℃ ℃. To compare with M seedling bed and P seedling bed, former seedlings rhizosphere average daily temperature and average the temperature decreased 2.6℃, 4.07℃, respectively, seedlings rhizosphere on an average day temperature greater than 25 high temperature duration decreased 4.92 h. Rhizosphere cooling temperature slows d℃ own the injury of the high temperature for seedling growth on the summer intensive seedling rhizosphere, with M seedling bed better cooling effect significantly, this may contact with thermal conductivity and larger contact area.Compared to two kinds of water-cooled seedling bed, root growth of tomato seedlings were superior to control seedling bed. Root length, root surface area, root dry weight and root activity were significantly increased compared with control. At the same time, improving the seedlings of plant height, stem diameter, leaf area and dry weight per plant. Compared with P seedling bed, M seedling bed seedlings root activity, leaf area and dry weight of per plant increased by 41.33%, 15.41% and 12.75%, respectively, the difference was significant. From the perspective of the physiological effects of two kinds of devices of seedlings, the MDA content decreased and significantly increased the content of chlorophyll when two beds does not affect the tomato seedlings under the condition of normal physical growth. Looking from the overall effect, M seedling bed of tomato seedlings growth is better than that of P seedling bed.2. The different periods of rhizosphere cooling effect on tomato seedling growthRhizosphere cooling process in the different periods of tomato seedlings rhizosphere accumulated temperature and daily average temperature were declined. While the most significant effect were M3 and M5, and accumulated temperature compared with control reduced 117.32℃ and 151.29℃, respectively, the average daily temperature compared with control reduced 3.36 ℃and 4.33 ℃. Rhizosphere cool all processing of rhizosphere temperature change trend and the trend of the change of temperature, but different rhizosphere cooling processing tomato seedlings rhizosphere temperature curve compared the daily change of more smoothly. Control seedling bed seedlings rhizosphere mean diurnal range temperature was 12.33℃, other processing of rhizosphere temperature daily range were less than controls, among them, M3 and M5 rhizosphere temperature daily range were only 5.15℃, 5.54℃.Rhizosphere temperature promoted the growth of tomato seedlings roots, its average root length, root diameter and root surface area have a different degree to increase. The unit root volume of root surface area was response the root development situation, M3 calculated value was 126.2, increased by 27.80%, and was the largest compared with all processing numerical, showed the best root development. Rhizosphere temperature and different processing plants of vegetative growth were better than comparison, among them, the M5 leaf area reaches the maximum of 79.02 cm2, promoting the seedlings photosynthetic accumulation. Also increased the root activity and chlorophyll content of seedling. Taken together, M3 and M5 seedling best and its root vigor respectively 48.71%, 42.58% higher than that of control, chlorophyll, respectively, compared with the control increased by 18.9%, 26.38%, significant difference were observed.3. The mechanism research of rhizosphere cooling relieve heat stress harm on tomato seedlingsRhizosphere water-cooled seeding bed significantly increased photosynthetic rate, transpiration rate and stomatal conductance of tomato seedlings. Compared with the control, The proportion of SOD, POD and CAT activity of tomato seedlings was improved 15.35%, 16.40% and 43.27% respectively, at the same time the content of MDA was reduced, all of these reduced membrane lipid peroxidation injury which was caused by high temperature and ensured the normal physiological activity of the seedlings.The rate of stem flow and root respiration can response the size of the seedling root activity, Water-cooled seeding bed significantly not only increased the root activity and nutrient absorption ability of tomato seedling under high temperature but also promoted the absorption for N, Ca, Mg element of tomato seedling which were increased 57.14%, 49.95%, 36.91% differentiate, while the content of Ca, Mg was significantly lower than the control seedbed. Uptake of nutrients from the tomato seedlings, the total absorption volume N, P, K, Ca, Mg were significantly higher than the control, of which the increased rate of N elements reached 105.44%. |
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