جستجوی مقالات مرتبط با کلیدواژه "ارس" در نشریات گروه "کشاورزی"

Drought is a major threat to vegetation and can cause its decline. Due to natural and human factors, droughts are becoming more frequent and intense around the world. This research examines the trend and severity of droughts in the past and future using the standardized precipitation evapotranspiration index (SPEI) for a Juniper forest reserve in Keygooran, Lorestan Province, Iran. The SPEI index was calculated using daily precipitation and temperature data from the Aligudarz synoptic station for a 33-year period (1987-2019). The frequency and severity of droughts were assessed for the recent past (1987-2019) and the future (2030-2060) using the NorESM2-LM model under the SSP126, SSP370 and SSP585 scenarios. The results showed that the longest droughts occurred in 1990-1991, 1998-2000 and 2010-2012. Moreover, 2003, 2013, 2017 and 2018 were the years with the most severe droughts. In the future (2030-2060), drought periods will be projected to decrease under the SSP126 and SSP585 scenarios (6, 9 and 12 months) and increase under the SSP370 scenario (3, 9 and 12 months). The intensity and duration of extremely severe droughts will be projected to increase in the future despite the decrease in drought frequency based on SPEI. Therefore, the Juniper forest reserve will face more severe droughts in the future, which will affect the reproduction of juniper trees significantly.

 Drought is one of the most important environmental stresses that affects various plants such as ornamental plants. The identification and selection of ornamental tolerant genotypes is essential for landscape projects. Understanding the mechanisms that enable plants to adapt to drought stress can help to select the most tolerant genotypes for cultivation in arid and semi-arid regions.

 For this purpose, a research was conducted as a factorial experiment based on completely randomized design with eleven genotypes and two levels of irrigation (irrigation as Control and severe drought) at Ramsar Citrus and Tropical Fruits Research Institute.

 The first symptoms of drought stress were observed after 10 days in the Juniperus horizontalis (G1) genotype (the most sensitive genotype) and were not recovered and dried after 15 days. G3 and G5 genotypes (Ravande-mamouli and Ravande-setarei, respectively) showed drought stress after 28 days (most tolerant genotypes) and recovered at the end of the stress period after irrigation. Drought stress decreased photosynthetic pigments in studied genotypes. The content of soluble sugars, proline, and total soluble protein increased under drought stress conditions and the highest amount was observed in G3 genotype 30.8 mg g-1 DW, 30.5 μg g-1 DW, and 965.2 μg g-1FW, respectively. Under drought stress condition, the highest concentration of hydrogen peroxide, malondialdehyde and electrical conductivity were observed in G11, G4, and G10 genotypes respectively compared to control plants. In addition, the most enzyme activity of superoxide dismutase (85.57%), total phenol (181.09%) and total flavonoid (98.46%) was evaluated in G3, G5 and G8 respectively. Also, chlorophyll changes indicate the response of plants to environmental stresses such as drought during drought stress, the concentration of abscisic acid and ethylene increases, which stimulates the activity of the enzyme chlorophilase and causes chlorophyll degradation. The reduction of photosynthetic pigments under drought stress also seems to be related to changes in nitrogen metabolism to proline production and reduced chlorophyll synthesis because the precursor of chlorophyll and proline is glutamate. Furthermore, one of the biochemical changes that occur in plants under drought stress is the accumulation of ROS. Numerous reports have stated that drought stress increases ROS production. Drought-induced oxidative stress causes lipid peroxidation and membrane damage. It seems that in some genotypes with low levels of malondialdehyde, the membrane damage is severe and leads to more electrical conductivity. Genotypes with more electrical conductivity are more damaged by drought stress. In some genotypes, such as G2 and G11, there was a positive correlation between malondialdehyde content and electrical conductivity, but in others, such as G1, there was a negative correlation. Although the amount of malondialdehyde in this genotype is low, electrical conductivity is very high. In other words, this genotype should be a genotype sensitive to drought stress. The tolerance of the plant to various environmental stresses may be related to the level of activity of the enzymes responsible for scavenging ROS. The antioxidant response to water scarcity depends on the severity of stress and type of plant species. Therefore, different genotypes increased their antioxidant activity to reduce the effects of oxidative stress, and the high antioxidant activity was observed for G5 compared with other genotypes which can be contemplated as drought-tolerant genotype. The accumulation of compatible metabolites such as soluble sugars and proline in plants under drought conditions can help to protect them against stress. The proline and soluble sugars accumulation under stress conditions reduce lipid peroxidation and acts as a free radical scavenger. According to the results, drought stress induced accumulation of proline and soluble sugars in the genotypes of Juniperus and the highest accumulation of proline was related to G3. Therefore, this genotype can be introduced as drought-resistant genotype.

 The results of the current study showed that drought stress significantly affected some biochemical parameters in all eleven genotypes. However, a variation in drought susceptibility was observed among genotypes. The studied genotypes in this experiment had different responses to drought stress and it seems that they utilized different mechanisms for stress tolerance. Genotype of G3 (Ravande -mamouli) was the most tolerant genotype to drought stress based on the highest levels of superoxide dismutase, soluble sugars, proline, and soluble protein. Genotype of G5 was also tolerant to drought stress with high superoxide dismutase activity and the largest amount of total flavonoid production. Therefore, increasing of compatible metabolites and antioxidant system are effective protective mechanisms against oxidative damage under drought stress.

Capoeta sevangi is a native species of the Cyprinidae family in the Caspian Sea basin (Arass River) and is ecologically and economically important. The main purpose of this study to investgate the relationship between absolute and relative fecundity with length, weight and age of this species in the Arass River and sampling was carried out from March to June 2012 using cast-net and gill-net. The result of the study on 72 female specimens of previous stages to prepare spawning showed that the absolute fecundity of this fish is 3056 to 21213 (10590.7±4085.0) eggs and the relative fecundity is 23.5 to 98.3 (41.1±11.9) eggs per gram of body weight and the egg diameter is 0.95 to 1.85 mm measured

Aras reservoir was established on the Aras River in border line of Iran and Azarbaijan. This is one the largest reservoirs in the country and deserved for its contribution in fisheries, drinking and agricultural water supply and recreational application in the region and country. This paper attempts to review Aras reservoir pollutions and phytoplankton blooms occurring in this freshwater ecosystem. The most conspicuous pollution resources of this reservoir were human activities such as agriculture (irregular use of fertilizers and pesticides), urbanization (absence of waste water purification systems), climate change and global warming. High levels of nutrients particularly phosphorous and nitrogen entered into the reservoir create harmful algal bloom particularly in warm and dry season. Cyanobacteria produced by blooms not only, have negative effects on the taste and odor of water and species diversity, but also, produce poisons that lethally impact on human and aquatic organisms. The algal species that induce blooms in the Aras reservoir were Microcystis botrys and Pseudanabaena limnetica. This review indicates that continuous monitoring of Aras reservoir and river water using physical, chemical and biological indices should be regarded as priority of research centers and related organizations.

Juniper trees are the native conifers of Iran extends in large areas of the country and is a factor to prevent soil erosion. However, the problem of Iranian juniper forest is the lack of natural regeneration. Therefore, the purpose of this study was to investigate the regeneration status of juniper plants in Jeyshabad (North Zanjan) repository at different times by using of Dendrochronology. In order to do this research, two plots were identified randomly in the protected and grazing areas, and samples were taken from all trees in each plot using increment borer. After preparing sample surface, ring width of the trees were measured and cross- dated. The results showed that the number of trees in the protected area is more than the grazed one. The mean diameter at breast height (DBH) of the trees in the protected area was lower, but in terms of average age, they were older than the trees in the grazing one. In the protected area, the number of trees in the age group of 10-20 years was remarkable, which showed that it had regenerated in the last two decades; while in grazing area, regeneration was affected and no new trees were observed after the period 1986. It was concluded that grazing decreased the regeneration of juniper and the growth pattern of the trees also changed; in a way that does not follow the form of natural growth.

Despite the importance of Arasbaran forests, no dendrochronological research has been conducted in this region, yet. In this study, for the first time, the potential of two juniper species, Juniperus foetidissima and J. oblonga was evaluated to be used in dendroecology. The first and the second species are respectively in the form of trees and shrubs in Arasbaran forests. Twenty-five trees of each species were samples and the sample preparation, ring width measurements, cross-dating, and construction of tree-ring chronology were performed according to the standard procedures. Developed tree-ring chronologies for juniper tree and shrub covered around 60 and 40 years, respectively. The statistics for evaluating the qualities of chronologies i.e. mean sensitivity (MS), signal-to-noise ratio (SNR), and expressed population signal (EPS) proved the capability of both species to study climate-growth relationships and reconstruction of climate. The relations between radial growth and climatic factors showed that both species have similar responses to climate: high temperature before the growing season promoted the growth while a warm spring reduced growth rate. Rainfall before the growing season had no meaningful effect on growth while spring precipitation strongly stimulated the radial growth. Overall, given the good distribution of juniper species in Arasbaran forest, the success of the developing ring-width series for studied junipers and its strong relationship with climate factors, these species can be used for dendroecological studies. For extending the length of tree ring chronology, juniper logs of old local buildings can also be used.

This research carried out to quantification of juniper stands structure in Kandragak region. For this purpose, three one-hectare study area were selected and the full calipering and the nearest neighbor’s methods were used to quantification of stand structure. Some indices including mingling index, distance to nearest neighbors, Clarke and Evans, and uniform angle and dimensional differences were employed to quantification of the stand structure. Results indicated the mean of DBH and crown coverage were 13.2 cm and 8.7 m2, respectively. Results showed mean value of Clarke and Evans and uniform angle indices was 1.05 and 0.45, respectively that revealed clumped or random distribution of juniper trees. The mean of mingling index calculated 0.14 among three study area showed low tendency of juniper to mix with other tree species. The mean value of distance to the neighbors was 3.70 meter and the height and diameter differentiation were 0.16 and 0.23, respectively. According to findings juniper in the natural habitats tends to be fairly pure in species composition and have slightly heterogeneous diameter distributions and uniform tree height. Accordingly, in the decision making and planning strategies, maintaining the natural structure and spatial pattern of trees have to be sufficiently considered

The aim of this study was to survey of quantitative situation of Juniperus stands for identifying affecting factors on growth and optimal establishment of this species. For this purpose, an area with 200 ha in Tarom, Zanjan province was selected. Random-systematic sampling was performed with 40 plots, each 1000 meter square area. In sample plots, collar diameter, the diameter of a half-crown, height, canopy, density and regeneration were measured. In each sample, a soil sample was taken to investigate soil characteristics. Analysis of variance results showed that there were significant deference in number/ha, height, canopy percent and regeneration between slope classes, in number trees/ha between aspect classes, in number trees/ha and canopy percent between elevation classes in 95% probability level. The correlation test results showed that between EC with number/ha was positive correlation. Soil acid saturation had positive correlation with the number/ha and regeneration. Nitrogen percent of the soil had positive correlation with the number/ha, percent of canopy cover and regeneration. Soil organic carbon percent had positive correlation with the number/ha, the diameter of the half crown and percent of canopy cover. P and K had positive correlation with diameter of half-crown. The percentage of sand had negative correlation with regeneration.

Analyzing spatial patterns of individuals within life stages and spatial associations between different life stages is essential for understanding the spatial and temporal dynamics of populations. This research was conducted to study the spatial patterns and spatial association of Juniper trees (Juniperus polycarpos C. Koch) at different life stages in Juniper forests of Layen, Northeast of Iran. Data collection was done using four one- hectare square sample plots randomly selected, which fully mapped. Spatial patterns and spatial association of different life stages (juvenile, premature and mature; based on crown diameter) were then analyzed using O- ring univariate and bivariate statistics, respectively. Results showed that the general spatial patterns of the trees in total and in every life stage was clumped at least up to 25 m, while after that tends to random distribution at larger scales. Spatial association analyses revealed that there was no significant intra-specific competition among life stages namely, the spatial association was positive (attraction) or indifferent. It is concluded that clump patterns are due to heavy fruit and dispersal limitation of Juniper trees and harsh environmental condition of the study area.

This study was performed to survey the site and silvicultural characteristics of Juniperus foetidissima Willd. in its exclusive habitat in the Arasbaran Biosphere Reserve. Measurements of height, canopy diameter, diameter of breast height, number of trees with single trunks, age, annual ring diameter, seedling density, health of canopy and quality of trunk were performed in 36 plots of 300 m² each distributed in three height, four aspect and three slope classes. In addition, soil profiles were excavated in 12 plots, in which samples were taken from surface and lower horizons. The measured samples were applied to determine the values of pH, EC, OC, N, P, K, Ca, Mg and Na, lime and soil texture. Except for annual ring diameter, abundance of trees with medium and low health of canopy and bad quality of trunk, the results showed significant differences of other vegetative characteristics among the three height classes. These attributes were significantly different in four aspect classes, while other differences in tree characteristics were not significant. Furthermore, all vegetative traits except the number of trees, abundance of trees with single trunks, abundance of trees with good health of canopy and excellent quality of trunk were not significantly different among the three slope classes. The results also showed that in different geographic aspects all the physical and chemical properties in surface and lower layers were significantly different. Finally, the J. foetidissima populations were associated with an old age structure and low regeneration. Full enclosure and planting seeds and seedlings of J. foetidissima will therefore ensure the sustainability of these populations in the future.

In order to investigate the effect of root pruning in morphological and physiological characteristics of Juniperus excelsa seedlings an experiment was carried out on transplanted one year-old seedlings. Treatments included root pruning intensities (1-slight pruning (2-moderate pruning and 3- control (no root pruning)). Experiment design was completely randomized design. Each treatment included three replicates and each replicate included 20 seedlings (in total 180 seedlings). The results showed that root pruning improved the quality and growth of root and seedlings survival. Results indicated that root pruning enhanced seedling quality index of J. excelsa seedlings and had a good capability for pruning. Root length, root diameter, root biomass, shoot biomass and total biomass were significantly correlated with habitat quality index which increasing these factors improves plant quality. The ratio of root to shoot biomass and total biomass was significantly correlated with plant survival. Survival was improved by increasing these factors. Also, according to high correlation between quality index and root collar diameter and on the other hand, another characteristics such as root length, root biomass is so hard to identification, root collar diameter is suitable index for qualitative classification Juniperus excelsa seedlings in nurseries.

The objectives of research were to create tree ring chronology of juniper trees and investigation on the relationship between the growth rate of the tree and the climate. Juniper trees are naturally distributed in High Mountain with semi-arid and arctic climate condition of Iran. Samples were collected from 20 trees in Shah-Kouh Mountain with 54° 42´ 58˝ longitude and 36° 61´ 01˝ latitude coordinate. Increment core were prepared and analyzed. The time span for tree ring chronology was 271 year (1741-2012 AD). Tree ring chronology statistic for MS، EPS، SNR، were 5. 6، 0. 85، 0. 29 respectively. Correlation between tree ring index and climate data showed that mean temperature in the previous growing season is an important factor for growth of juniper trees. The result of this research can help the development of climate data and is useful for the creation of weather atlas.

Mountainous forest communities of Irano-Turanian vegetation region are characterized with Juniperus excelsa. These forests have involved too many changes in the past and nowadays mostly are not integrated. But there are still some dense or broad stands. In this research، we have studied such these communities and their ecological properties in north of Tehran to northwest of Semnan province. A data set including floristic data according to Braun-Blanquet method and environmental variables were provided. To classify the vegetation، TWINSPAN and analyzing vegetation data with JUICE، and to investigate the species-environment relationship، ANOVA and Ordination (CCA and PCA) was used. According to the results، the vegetation was classified into six groups which were specific in floristic composition and ecological characteristics، and were described by their site properties، constant and indicator species. These groups took placed in three forest communities: Juniperus excelsa - Rhamnus pallasii، J. excelsa - Cotoneaster nummularius and J. excelsa - Lonicera iberica. The first one is significantly related to lower altitude and soils with poor nitrogen and organic matters، the second community is interested in upper lands and nutrient soils with a high saturated water capacity and the third one comprises stands impressed by the moist climate of the Hyrcanian region.

In order to analyze the quantity of Juniperus stands spatially and statistically and their relationships to topographic and edaphic features, an area of 4700 ha was selected in the Chahar-Bagh region at the Gorgan. The maps of slope, aspect, elevation and geology in GIS environment were overlaid to generate homogenous landform units. In each unit, some 0.1 ha sample plots were randomly selected in GIS environment. 149 sample plots were established in the field. Within each sample plot, diameter at breast height, number of trees, canopy cover and height of trees were recorded. Analysis of variance (ANOVA) and Duncan comparative analysis were used to compare the properties among landform unites. The results showed that landform units were different significantly in terms of number of trees per hectare, canopy cover percentage, mean diameter of basal area and basal area at breast height. Results of nonlinear regression model showed that aspect and wetness index were the best predictors for the number of trees per hectare (R2adj= 0.57). Also a nonlinear component of aspect, stone and wetness index were the best predictors for modeling the canopy cover (R2adj=0.49). In addition, a nonlinear component of variables containing aspect, stone, wetness index and stream power was the best model for basal area at breast height prediction (R2adj= 0.56). A nonlinear component of variables including the aspect, stone, stream power and wetness index were also the best predictors to model the diameter of basal area at breast height (R2adj= 0.50).

One of the problems in most of the Juniprus excelsa habitats is the lack of regeneration which presents itself as a challenge for their revival and future. The dispersion of these regenerations is not similar under all of the trees. The soil and its components also play a significant role in their formation. The plant roots and micro-organisms produce soil enzymes. Hence, their presence in different food cycles of the soil might release the nutritional elements and make them available for plants and their regeneration. The present study was carried out in Chahar-Bagh habitat of Gorgan in an attempt to investigate and compare the possible influence of the soil enzymes and microbial biomass on the rhizosphere of the Juniperus trees with/out regeneration. Samples were collected from the soil around the roots of trees with/out regeneration. After extracting the juice, the activity of the acid and alkaline phosphatase, dehydrogenase, and urease was measured using the substrate and microbial biomass reactions by means of a spectrophotometer. The results indicated that these enzymes and the microbial biomass had more activity in the trees with regeneration in comparison to those without regeneration. This might be due to the existence of more micro-organisms such as mycorrhizal fungi in the root of these trees and the better absorption of food elements and materials.

Structure study of the forest is one of the important subjects of silviculture close to nature. Recognition of Juniper forests as the main structure of natural forest ecosystems, is necessary for the degradation process. In this research, in order to study the structure of natural Juniper stand in protected forest, 49.53 ha of Juniper stand was selected (Khalkhal forests) and 100% inventory was applied. Forest stand characteristics including species mixture, number per hectare, diameter at breast height, total height and crown diameter were measured and analyzed. Results show that the stand is basically uneven-aged and Juniperus excelsa is the dominant species. The mean forest canopy, mean basal area and mean number per hectare are 42.85%, 4.68 m2 and 592, respectively. The stem number frequency of tree in diameter at breast height shows an uneven-aged pattern. Totally, the study of stand in terms of structural is a mixed, unevenaged and open canopy cover stand.

In order to investigate on qualitative and quantities characteristics of Juniper stands, a 613 ha case study area was chosen in the Aminabad of Firouzkoh. In this study, the stratified sampling method was used and the study area was stratified to homogenous regions based on slope, aspect and geological unites in GIS environment. By combining the slope and aspect maps, we made the landform unit map. Landform unit map and geology map were then overlaid to produce the homogenous unit map. Then 42 units randomly selected for forest inventory and in each unit randomly one point specified as centre of cluster. After visiting the study area, the Juniper coverage were observed only in 20 clusters and others clusters were bare and without Juniper coverage. In conclusion, in the 20 clusters containing the Juniper trees, center and other 4 points around them in main geographical aspect in distance about 50 meters from centre of cluster have considered as plot with 1000 m2 area. In each plot, tree height, diameter at breast height, coppice or seeding crop, sexuality, crown canopy area, slope percentage and geographical aspect were measured and computed for each cluster in terms of hectare. Relation analysis by ANOVA test was used for differentiation test between clusters based on qualitative and quantities characteristics of Juniper stands. The results shown that in the study area the juniper stands are as irregular even aged stands with the left skew ness in point of distribution of trees in diameter class. Results showed an intense decreasing in 30 cm diameter class regenerations due to human activities and close to road and village of Aminabad. In addition, result of canopy cover density in the study area showed that the Juniper stand of Aminabad is thinner in comparison with other studied Juniper stands. The mean, maximum and minimum of tree density in each plot was 31.5, 170 and 0 in hectare respectively. The mean, maximum and minimum tree height in the study area was computed 4.9, 10 and 2 meter, respectively. The maximum measured DBH of juniper trees was 62 centimeters. Also the mean, maximum and minimum canopy cover of study were 750, 2470 and 0 m2, respectively. According to qualification, the percent of seeding crop trees in the whole stand is more than coppice trees and between male, female and ambisexual, we can see females are more than the other kinds.

Juniper forest with 3400 hectares area in the north of Ghazvin province includes a mixed type of two different species; Juniperus excels M. bieb and J. communis L.. Unfortunately, the natural regeneration of these valuable plants decreases continuously as a result of human and livestock interventions such as shoot cutting and grazing and some arthropod pests as juniper berry miner moth that feed on fruits and seeds and is the subject of present study. The research was conducted in Hossein Abad Tarom (1800 meters altitude) 45 km to west Loshan in 2009-2011 periods. Samples were collected in three different sites with different geographical altitude. For studying biological features of the moth, samples were taken bi-weekly throughout fruit ripening period in the growing season. In this research Argyresthia praecocella was identified on the Juniperus excels fruit. Based on the results, this pest produces one generation per year. Larval feeding activity damages exo-carp of juniper fruit. The larval activity inside the fruit, starts from August and continues through December. This insect overwintered as pre-pupa under juniper bark. Adult moths emerged from late April till early Augusts in this area, and after mating lay their eggs on newly formed juniper fruits. Based on Dayars index, the pest has five larval instars.