نشریه خشک بوم
سال یکم شماره 4 (پاییز و زمستان 1390)

Different responses of some weed species to Peganum harmala L. allelochemicals requires to find resistant species to this plant (with high allelopathy potentiality) in order to improvement of critical rangelands. In order to determine allelopathic potential of Peganum harmala L. on two important rehabiting species such as Agropyron desertorum and Agropyron elongatum, the effects of factors of this donor plant as kinds of powder (aerial and uederground parts), propertion levels (0, 5, 10, 15 and 20%) and phenology stages (vegetative, flowering and seeding) were measured on germination (speed and percentage) and grow (root and stem length) indices in factorial design with 3 replications. Another experiment was done to investigate the effects of natural habitate soil in a rondom design with 3 replications. Allelochemicals effect in seeding stage on all dependent variables of two recipient species was lower than vaegetative and flowering stages. All indices was decreased with an increase in powder propertion. Significanthly negative response of germination and growth indices was observed in allelochemicals of aeria part and this response was severe in Agropyron desertorum Considering the negatively lower response of Agropyron elongatum to large amount of Peganum harmala dry matterr powder the effects of natural habitate soil, Agropyron desertorum is prefered for improving rangelands with Peganum harmala bed. Harvesting of aerial parts of Peganum harmala before and after rehabitation projects are recommonded for decreasing of its allelopathic effects.

The main objective of this research is to measure the impact of land use changes and biological restoration on C and N storage in some arid rangelands of Semnan province covered by Artemisia sieberi species. In this study two sites in Ghooshe and Ivanaky were selected. To estimate C and N storages and their distribution in the different treatments, biomass (above ground and below ground), soil (0-25, 25-50, 50-75 cm) and litter factors were sampled and analyzed. Results show that both land use change to Haloxylon ammodendron and Pistachia vera plantations have increased 89% and 185% in carbon and 84% and 172% in nitrogen of biomass, respectively. However H. ammodendron plantations have increased C storage of soil but pistachio has decreased C and N storages of soil. Generally Haloxylon plantation has considerably increased fixation carbon and nitrogen of the ecosystem. Similar results are not observed for land use change into pistachio plantations. The reasons of this observed differences result may be related to more extension of root biomass in Haloxylon in compare with Pistachio and effect of agriculture practices on decreasing C and N storage of the soil.

Arid lands of Iran, such as Yazd province, are the main regions for cultivating and economic production of pomegranate (Punica granatum L.). Low precipitation, dry and warm summer, cold winter and environmental stress, especially drought and frost, are ecological characteristics of these regions. Based on some important climatological indicators, coldness and frost in January 2008 was an unexpected event for Yazd province and other desert areas in Iran. Therefore, study of chilling and frost effects on pomegranate were conducted and continued for 2 years. Number of 180 pomegranate orchards were visited in the main centers of pomegranate production and questionnaires were completed by interviewing with gardeners. Data of these questionnaries were analyzed by using one sample T-test in SPSS. Simultaneously, 22 sites were selected in the main pomegranate production centers of Yazd province. In each site, 3 orchards with good, normal and weak quality of management and in each orchard 10 trees of prevailing cultivars, were randomly selected. In the next step, several factors such as intensity of damage on these trees were studied. Results show that due to coldness and frost in winter, most of pomegranate orchards were damaged. Sweet cultivars comparing to sour, white skin comparing to red skin, old trees comparing to young and gardens with weak management comparing to good management were effective on yield, fruitquality and tree damage. However, these frost resistances were broken in severe frosts and all cultivars of pomegranates were damaged. Roots were safe against frost and were produced plentiful shoots in all cases, even in regions with a minimum temperature of -24 C˚ in winter

Lithology of large part of Lamerd rangelands in south of Fars province is Bakhtiari geology formation. Sandstone and conglomerate rocky slopes in this geology formation were analyzed in this study area. Then, several factors affecting on plant canopy were evaluated in both field and laboratory studies. In regard to the changes resulting from water erosion and slope, areas with the slopes of less than 100% (perpendicular to the layers along rocky) and slopes of more than 100% (on rock layers) were selected for taking samples. In each site, 35 transects with a length 5 m were randomly laid out throughout the study area in north aspect and along those transects, percentage of vegetation cover and numbers of large crack wide, medium crack wide, small crack wide, large crack depth, medium crack depth, small crack depth, large crack length, medium crack length, small crack length were measured. In addition, laboratory tests were conducted to measure soil characteristics and moisture content of the soil inside the cracks. Analysis of soil properties showed that the moisture content was significantly differed (p<0.05) among the three depths of 0-10, 10-30 and 30-50 cm in both sandstone and conglomerate rocky. But, the differences between other soil properties were insignificant statistically. Results indicate that there are significantly differences between crack properties in vegetation cover in the conglomerate and sandstone rocks and between two slope classes in each rock. Moreover, vegetation cover has positively significant relationships with increase of crevice wide and depth in each lithologic unit. It was concluded that the differences of crevice properties could be prominent role in vegetation cover changes in the crevice characteristics could be related to rocky type and stratigraphy in different slopes.

Range management concerns the important knowledge on indicator plant species, in particular, their ecological behavior in relation to the main environmental variable. This study aimed to assess the effect of important environmental variables such as rainfall and soil characteristics on Artemisia sieberi species in the steppe region of Yazd. For this purpose, 14 various habitats of this plant species were selected and their canopy cover and forage yields were measured using plot-transect method in each year. For each sampled habitat, one composite sample was collected from profiles of 0-40 cm depth. Measured soil properties were included: gravel, texture, organic matter, calcium carbonate (TNV), gypsum, pH, EC, soluble ions (Na+, Mg2+ and Ca2+) and SAR. Rainfall data was collected from nearby climatological stations. The relationships between A. sieberi and environmental variables were determined using of Redundancy Analysis (RDA) method. Application of RDA indicated that on the first canonical axis, mean annual rainfall, organic carbon, percentage sand content and EC have the highest intra-set correlation (r = 0.8, r = 0.63, r = -0.74 and r = -0.38), thus were as the strongest effective environmental variables for Artemisia sieberi growing parameters. Calcium carbonate (TNV) and saturation percentage (SP) showed significant correlation with CCA axis 2 (r = 0.65 and r = -0.43) and had lower effect on this species. These mentioned environmental gradients accounted for 83% of the species–environment relationship among the study sites.

This study aimed to compare soil seed bank characteristics (density, diversity, richness and its similarity with above ground vegetation) between grazed and ungrazed areas, and between two different depths, 0-5 and 5-10 cm in rangelands of Kahnuj, Kerman province. Thirty plots in 2×2 m dimentions in ungrazed area and 135 plots in grazed area were established. Soil samplings were collected in each plot in two different depths after seed dispersion. The cover percentage of all vascular plants was estimated during the next growth season. Soil samplings were then treated in a cold condition for three months and were transported to greenhouse to allow viable seeds to germinate. All seedlings germinated in the greenhouse were identified and removed after identification step.Soil seed bank density per square meter, seed composition richness, seed diversity and similarity between soil seed bank and above ground vegetation were calculated for each plot and for each depth. Non parametric test (Mann-whitney U) was used to compare soil seed bank characteristics between the two depths and between grazed and ungrazed areas. Results showed that soil seed bank density and similarity between seed bank and above ground vegetation were higher in ungrazed area than grazed area. All studied seed bank characteristics were higher in upper soil layer than deeper soil layer. Generally, it can be concluded that the exclosure can be improved vegetation by soil seed bank in this area.

Germination of plants as an important growing stages, are often influenced by environmental stresses, particularly drought and salinity. In order to study the germination of Anabasis calcarea, different levels of salinity and drought in two separate experiments and in three replications, were conducted in a randomized complete design. The experiments were conducted using drought stress with 5 levels of concentration (Control, -3, -7, -11 and -18 bar) and salinity stress also were done with 6 levels (Control, -3, -7, -11, -18 and -36 bar). Drought stress induces with PEG600 and salinity stress applied using two salts, including NaCl and mixed NaCl and Na2SO4 in ratio of 1:1. Results show that high levels of salinity and drought reduces the rate of germination, plumule and radicle length significantly (P<0.05). The germination percentage of Anabasis calcarea in drought stress of -11 bar and salinity of -18 bar in two treatments of NaCl and NaCl + Na2SO4 were 95.5%, 66.5%, and 81.8%, respectively. It can be concluded that decreasing in germination percentage of the species is due to the decrease in osmotic potential. General results show that the Anabasis calcarea is resistant to drought and salinity.