بررسی اثر سیانوباکتری‌های بومی دشت سجزی بر کنترل فرسایش بادی در شرایط آزمایشگاهی

برای مقابله با پدیده مخرب بیابان‌زایی، روش‌های مختلف مکانیکی، شیمیایی و بیولوژیکی کشت نهال‌های سازگار یا کاربرد خاکپوش‌های زیستی پیشنهاد شده است. در این پژوهش، سیانوباکتری‌های بومی دشت سجزی پس از جداسازی، کشت، خالص‌سازی و شناسایی، تکثیر شد و از نظر کلاس بافت خاک، به صورت محلول در آب و با وزن زیست توده 2.5 گرم در لیتر بر روی خاک‌های مختلف اسپری شد. این امر به روش آب تلقیحی و با توجه به حجم منفذی بر روی نمونه‌های خاک صورت گرفت. همچنین مونومر‌های ترکیبات پلی‌ساکاریدی از جمله مانوز، زایلوز، آرابینوز و گلوکز، به روش کروماتوگرافی مایع شناسایی شد، سپس مقدار آنها اندازه‌گیری و به همان نسبت محلول آنها تهیه و بر روی ‌نمونه‌های خاک اسپری شد. سرعت آستانه فرسایش بادی و میزان بادبردگی در سرعت‌های مختلف باد نیز با استفاده از تونل باد به صورت فاکتوریل، در قالب طرح تصادفی با سه تکرار اندازه‌گیری شد. در ادامه، مقادیر مقاومت فشاری و برشی خاک نیز اندازه‌گیری شد. طبق نتایج آزمون تجزیه واریانس یک طرفه، میانگین بادبردگی در سرعت 7.15 و 15.06 متر بر ثانیه، با تیمار سیانوباکتری و بافت خاک رابطه معنی‌داری داشت. در سرعت 11.21 متر برثانیه نیز این مقادیر تحت تاثیر کلاس‌های بافت و درصد رطوبت خاک قرار گرفت و با تیمار سیانوباکتری رابطه معنی‌داری نداشت. افزودن سیانوباکتری‌ها به خاک، به افزایش مقاومت برشی خاک در برابر نیروی کنش باد منجر شد. نوع بافت و درصد رطوبت خاک، با مقادیر مقاومت برشی رابطه معنی‌داری نداشت. سیانوباکتری‌ها در خاک‌های لوم و لوم سیلتی نیز بهتر از انواع دیگر خاک استقرار یافت و همین امر، در شار تلفات خاک تاثیر گذاشت، اما به دلیل حساسیت ذرات کوچک‌تر از 0.84 میلی‌متر به فرسایش بادی، تیمار سیانوباکتری در سرعت 11.21 متر بر ثانیه معنی‌دار نشد. با توجه به طبقه‌بندی usda خاک‌های fine sand و very fine sand برای تثبیت با سیانوباکتری‌های microcoleus vaginatus و coleofasciculus chthonoplastes مناسب است.

Investigation of the Effect of Native Cyanobacteria in Sejzi Plain on Wind Erosion Control in the Laboratory

1 IntroductionThe destructive phenomenon of desertification, in addition to land degradation, and causing environmental problems and dust events, exert great damages to human societies such as damage to transmission lines, and blockage of roads and railways. Various mechanical, chemical, and biological methods have been proposed to deal with desertification. Recently, in different parts of the world and some parts of Iran, biological soil crusts have been used as biological improvers to modify and stabilize the soil against desertification. Biocrusts consits of a collection of lichens, mosses, algae, fungi, bacteria, and cyanobacteria that play a major role in soil regeneration, increasing desert ecosystem performance, and combating desertification. Researchers have identified the addition of cyanobacteria to the soil as an effective way to improve soil and increase soil ecosystem performance, especially in desert areas. For this purpose, cyanobacteria are used alone or in combination with plant cultivation.2 Methodology The study area is part of the Sejzi Desert (Central Deserts of Iran) which is located in Isfahan province of Iran. Wind erosion threshold speed was measured in Sajzi plain using a portable wind tunnel. After plotting the storm rose by the data obtained from the synoptic station of Shahid Beheshti Airport in a period of 25 years from 1991 to 2016 by using WR Plot 7 software in different seasons, the speed and frequency of winds were determined. For conducting the intended experiments, 4 soil samples were collected from the area with biocrust cover and 4 other samples from the area without biocrust cover. PH, EC, OC, saturated moisture content, MWD, dry grain size distribution and soil texture were measured for soil samples. Carbohydrate monomers were identified by HPLC. For the culture of cyanobacteria, very small pieces of soil undercovered with cyanolichens were placed on BG 11 medium, and the processes of isolation, culture, and purification were done, respectively. After sieving the soil through a 4.75 mm, the wind tunnel trays in the dimensions of 30 x 50 x 8 cm with an area of 1500 cm2 were filled with soil and their surface was smoothed. The control trays were also saturated to a depth of one centimeter with a distilled water. The amplified cyanobacteria were then isolated from the culture medium under a BX51 light microscope and prepared in a water solution with a biomass weight of 2.5 g/l by inoculated water method and in the required amount according to the pore volume and were sprayed on soil samples. Mass fluxes were measured for all soil classes at different wind speeds according to the erosion threshold speed between 7.15 to 15.06 m/s. Shear strength and soil moisture were also measured. Experiments were performed completely in a randomized design in three replications.3ResultsThe wind erosion threshold in the center of the Sejzi plain was 3.76 m/s on the sandy loam soil texture. Most wind erosion occurs in late winter and early spring. In spring, 35.8%, and in winter, 21.9% of winds had a speed of 711 m/s. The EC, sand, and silt were lower, in the soil undercovered biocrusts, but saturation moisture, MWD, clay, and OC were higher. Of the four identified monosaccharides, arabinose was found in all three samples, but its amount was different in soil samples. Also, Mannose and Xylose were identified and measured in only one of the soil samples at 0.01% and 0.02%, respectively. Based on morphological characteristics, two specimens of cyanobacteria including Microcoleus vaginatus and Coleofasciculus chthonoplastes were identified. In samples treated with carbohydrates, there was no change of mass fluxes and threshold velocity of wind erosion, and shear strength with control samples. According to the results of the ANOVA test, the mean winding at different wind speeds was affected by soil moisture and texture and treatment with cyanobacteria. By speed of 7.15 and 15.06 m/s, mass fluxes had a significant relationship with cyanobacterial treatment and soil texture. At 11.21 m/s, sediment yield values were affected by texture classes and soil moisture content and had no significant relationship with cyanobacterial treatment. The results showed that the addition of cyanobacteria to the soil increases the shear strength of the soil against the wind force. Texture type and soil moisture percentage had no significant relationship with shear strength values.4 Discussion Conclusions The central parts of the Sejzi plain were sensitive to wind erosion in terms of soil characteristics and compared to its peripheral strip, wind erosion was more intense and had destroyed the plain soil. The presence of microorganisms in the soil and its successive proliferation increases the organic content of the soil and increase soil stability, while adding a certain amount of carbohydrates artificially in the soil surface layer, especially in natural resources, leads to their decomposition by environmental conditions and climates such as ultraviolet rays and their function in the soil is reduced and may even stop. Cyanobacteria are better established in loam and silty loam soils than other types of soil and this has affected the soil loss flux, but due to the sensitivity of particles smaller than 0.84 mm to wind erosion of more particles at a speed of 11.21 m/s, cyanobacterial treatment was significant. The difference between the samples treated with cyanobacteria was due to the resistance of fine particles between the filaments of cyanobacteria Microcoleus vaginatus and Coleofasciculus chthonoplastes. According to the USDA classification, the range of soil particles for Fine Sand and Very Fine Sand varies from 0.25 to 0.05 mm and are suitable for stabilization with Microcoleus vaginatus and Coleofasciculus chthonoplastes cyanobacteria.