H. Nastari Nasrabadi; S.F. Saber Ali
Abstract
Introduction: Melon (Cucumis melo L.) is one of the most important vegetables in Cucurbitaceae family and one of the most important economic crops in the Torbat-e Jam city (Longitude: 60 ̊48', latitude: 35 ̊31', altitude: 928 m). Growth and yield of agricultural crops are affected by biotic ...
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Introduction: Melon (Cucumis melo L.) is one of the most important vegetables in Cucurbitaceae family and one of the most important economic crops in the Torbat-e Jam city (Longitude: 60 ̊48', latitude: 35 ̊31', altitude: 928 m). Growth and yield of agricultural crops are affected by biotic and abiotic environmental stresses. Cold stress can be one of the most important environmental factors reducing crops yield. Cold acclimation in plant is a complex process involving many morphological, physiological and biochemical changes, including a significant reduction in tissue hydration during cold hardening. Melatonin (MEL, N-acetyl-5-methoxytryptamine) is a conserved substance, which has been discovered in all living organisms, from bacteria to mammals. MEL regulates the growth of root, shoot, and explant, activates seed germination and rhizogenesis, and delays leaf senescence. In addition, the most frequently mentioned functions of MEL are related to various abiotic stresses such as drought, radiation, low/high temperature, heavy metals, and salinity stresses. Materials and Methods: In order to investigate the effect of PEG priming and melatonin on cold stress resistance of melon seedlings, a factorial experiment was conducted in a completely randomized design with three replications in Torbat-e-Jam University. In this experiment polyethylene glycol 6000 was used to produce drought stress at three levels (0, 0.18 and 0.58 MPa) and melatonin was used at two levels (0 and 200 μmol). When melon seedlings were at 4 leaf stage, the amount of polyethylene glycol was added to the irrigation solution for a week and to prevent drought stress, drought stress was increased for 3 days and increased one third of the required concentration daily. Recovery was performed for three days after drought stress and during this period melatonin was added to the irrigation solution at the required concentration. Seedlings were then exposed to cold stress (T0: non-stress and T1: cold conditions). Control plants were kept in greenhouse conditions. Results and Discussion: Comparison of the mean results showed that there was an increasing trend in proline production by increasing drought stress. The highest amount of proline (0.80 µmol g-1 FW) was recorded at the highest level of drought pretreatment with no melatonin and without cold stress (D2M0T0), and then a decreasing trend in proline production was observed. The results showed that melatonin significantly increased leaf relative water content compared to the control. Interaction effects of drought pretreatment and temperature showed that there was a trend of decrease in relative water content by increasing drought pretreatment. Ghanbari and Sayyari (8) reported that drought pretreatment stress maintains relative water content of tomato seedlings under cold stress conditions. Drought pretreatment significantly reduced the amount of chlorophyll a and total chlorophyll. The results showed that the highest levels of drought pretreatment stress (D2) and melatonin (M1) maintained chlorophyll a under cold stress conditions. Results showed that the amount of chlorophyll b was decreased by drought pretreatment stress, but it increased by melatonin application in all compounds. Based on the results, it was found that only simple effects of treatments at 1% of probability level had significant effects on soluble sugars content. Comparison of the mean simple effects of drought pretreatment showed that under drought stress the amount of soluble sugars increased significantly and the highest sugar content was recorded at the highest drought stress level. The amount of soluble sugars in plants under cold stress also increased significantly. Melatonin application also significantly increased the amount of soluble sugars. Kabiri et al. (19) reported that the use of melatonin increased soluble sugars in Moldavian balm seedlings under osmotic stress which is similar to this study results. It was found that melatonin significantly increased phenolic compounds under stress conditions and significantly decreased electrolyte leakage.
zahra karimian; Ali Tehranifar; Mohammad Bannayan; Majid Azizi; Fatemeh Kazemi
Abstract
Introduction: Considering population growth and urbanization development, one of the main requirements of the urban society is to create appropriate life condition for dwellers. The microclimate is considered as one of the factors that affect the activity of people in the environment and in terms of ...
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Introduction: Considering population growth and urbanization development, one of the main requirements of the urban society is to create appropriate life condition for dwellers. The microclimate is considered as one of the factors that affect the activity of people in the environment and in terms of tourist and recreational industry, it is considered as an important source of economic. Many climatic parameters such as temperature, relative humidity, radiation and wind speed can affect the quality of people's recreational activities. So far, many studies have been conducted in the world about the positive effects of vegetation specially trees in the urban landscape on the optimizing of microclimate and human thermal comfort. The cooling mechanism of trees and clouds in an area mainly by directly shading the ground surface and indirectly by supplying humidity are similar. Thus, perhaps it be possible to calculate the changes in temperature and relative humidity based on cloud categories and impute it to tree canopy and vegetation size. The purpose of the present study was to answer followed questions, 1) does the use of single tree produce a sensible difference in temperature and humidity relative to open space? 2) Does the acacia tree as an indicator for a broad-leaved species compare to the pine tree as an indicator for the needle species in terms of the microclimatic variation of around themselves act differently? 3) Do the microclimatic elements (Temperature and relative humidity) under the canopies are comparable to various cloudiness conditions?
Materials and Methods: The experiments were conducted at Ferdowsi University of Mashhad. The climate data under two species of false acacia (Robinia pseudoacacia) and pine trees (Pinus eldarica) and open space were received from Mashhad weather station over a period of 19 years, recorded and analyzed. In the comparison of the effects of vegetation and cloudy conditions on the temperature and relative humidity an assumption was proposed that has been mentioned in the following. The differences between the means of temperature and relative humidity obtained under SKC (Sky Clear) cloudiness conditions and in open space; under SCT (Scattered Sky) conditions and pine trees; and under BKN (Broken Sky) conditions and false acacia tree must be equal or these differences must be statistically not significant. In addition to the effect of tree canopy, the effects of days and hours on the temperature and humidity were investigated. To analysis and also mean comparison, SPSS 16 software was used.
Results and Discussion: The results showed that the temperature (decreasing) and relative humidity (increasing) were significantly different among various cloudiness conditions during 19 years. The results also indicated that between the temperatures recorded under the canopy of pine and false acacia trees, and also among of recorded relative humidity in two trees specious with corresponding outdoor spaces there were significant differences. Also, there were no significant differences among the temperature of the clear sky and the partly cloudy with that of the mostly cloudy sky. Further, clear sky and mostly cloudy sky showed significant differences in terms of relative humidity. Mostly cloudy sky and the partly cloudy sky compared with pine and false acacia trees were about 4.6 and 4.5oC cooler, respectively. The cloud covers, also could enhance the more level of relative humidity in the environment in comparison with single tree canopy, so that were caused a wetter environment equal to16.6 and 8.4 percent, respectively. The results also showed that temperature and relative humidity created by the shade from false acacia and pine trees are not comparable with the same climatic factors created by partly cloudy and mostly cloudy skies. In the present study, false acacia as a broad-leaved tree compared with pine tree and also open space could cool the environment about 0.65 degree C more that is in line with previous studies that showed the microclimatic impact of vegetation depend on crown and leaf size. Temperature and relative humidity in vegetation (trees) and cloudy condition are not comparable with microclimate and their impact on the environment is not the same. The cloud covers, also could enhance the more level of relative humidity in the environment in comparison with single tree canopy, so that were caused a wetter environment equal to16.6 and 8.4 percent, respectively.
Conclusion: This finding showed that climatic effects of cloud covers had no similarity compared with two studied trees species. It may also indicate that green space and greenery should not also be ignored in areas where cloudy skies are mostly present throughout the year.
zahra karimian; ali tehranifar; Mohammad Bannayan; majid azizi; fatemeh kazmi
Abstract
Introduction: With regard to two adverse climatic phenomena of urban heat islands and global warming that has been leading to increase temperature in many cities in the world, providing human thermal comfort especially in large cities with hot and dry climates, during the hottest periods of the year ...
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Introduction: With regard to two adverse climatic phenomena of urban heat islands and global warming that has been leading to increase temperature in many cities in the world, providing human thermal comfort especially in large cities with hot and dry climates, during the hottest periods of the year is crucial. Mainly vegetation with three methods: shading, evapotranspiration and wind breaking can affect micro-climate. The aim of this study was to asses and simulate the impact of existing and proposed vegetation on the human thermal comfort and micro climate changes in some residential areas of Mashhad during the hottest periods of the year by using a modeling and computer simulation approach.
Materials and Methods: This research was performed in the Ghasemabad residential area, Andisheh and Hesabi blocks, and in the hottest period of the year 2012 in Mashhad. Recorded data in the residential sites along with observed data from Mashhad weather station that included temperature, relative humidity, wind speed and direction. Soil data (soil temperature and humidity, soil\ type), plant data (plant type, plant height, leaf area index) and building data (inner temperature in the building, height and area buildings) as input data were used in the ENVI-met model. Both two sites, Andishe and Hesabi residential blocks, with vegetation (different trees and bushes plants, for example Acacia, ash, sycamore, mulberry, chinaberry, barberry, boxwood and Cotoneaster that all of them are tolerant and semi-tolerant to drought) about 20% were simulated. Regarding the area of simulating, 3 receptors were considered in per sites. Simulation was commenced from 6 AM and continued until 18 pm, but just data of 11-15 hours were analysed (the hours of peak traffic).
Results and Discussion: Analysis of outputs data revealed that the temperature of two residential sites in all three receptors during the study were almost the same. In general, the maximum temperature difference between receptors was obtained at 13 hour. The trend of relative humidity changes was very similar in both residential sites. In these two sites the most differences in the relative humidity was obtained at 12 oclock.. In addition, the trend of Predicted Mean Vote (PMV) in Andisheh residential block showed that these changes in central and south-west part of the site were similar. The simulation with vegetation in the sites, also, showed that the trend of temperature and relative humidity changes were similar. The trends of temperature changes in residential site, Hesabi, in the defined receptors were very similar. So that temperature increased from 12 oclock to 15. While the trend of relative humidity changes was quite the reverse. This study results showed that the difference in temperature, relative humidity and PMV between measured and simulated data were minimal in both residential sites. Moreover, the data comparison of PMV indicated that in both residential sites, despite of simulation with vegetation, the human thermal comfort did not improve, so that these sites were in the range of extreme heat stress. There are several reasons to justify this issue, such as the percentage and the type of vegetation, factors related to the topography and geography of area, building distribution and density, type and color of the building materials and surfaces, etc. However, in this part of the study, other factors were constant, except vegetation. It seems that with increase of percentage and the ratio of vegetation, changes in temperature, relative humidity and other micro-climate factors, are created, but sometimes for the reasons stated, the temperature during the hottest period of the year is too high so that increase in vegetation will have little impact on outdoor thermal comfort. It might be the simulated area on these sites as well as the type and the ratio of the selected species to reduce the temperature and increase the relative humidity have been not adequately represent all conditions which be able to improve thermal comfort.
Conclusions: In this study eventually we can conclude that in the simulated sites with about 20 percent vegetation cover,, despite the slight decrease and increase in temperature and relative humidity, respectively compared with the real sites, the thermal comfort range was similar. It is advisable in the future studies to simulate the green area in shape of the vertical and horizontal, changes in species composition in green area like trees, shrubs, and cover plants and also the test of different combinations of type and percentage of vegetation.
