Abstract:
با فراهم کردن شرایط مناسب برای فعالیت خوب میکروارگانیسمها میتوان به افزایش هر چه بیشتر کیفیت خاک، کاهش فرسایش و هدر رفت آن کمک بسیاری کرد. به منظور بررسی تأثیر جهت شیب، طبقات ارتفاع و کاربری بر تنفس میکروبی پایه و تحریکشده خاک و همبستگی این شاخصهای زیستی با سایر خصوصیات خاک، پژوهشی در یک منطقه در اطراف روستای خانقاه شهرستان نمین واقع در استان اردبیل صورت گرفت. این پژوهش با برداشت 72 نمونه به صورت شبکهبندی منظم اجرا شد. فاکتورهای آزمایش شامل کاربری اراضی در سه سطح (کشاورزی، مرتع و جنگل)، جهت شیب در دو سطح (شمالی و جنوبی) و دو طبقه ارتفاعی (1580دار رطوبت مزرعه بود. همچنین نقشه تنفس میکروبی خاک به روش کریجینگ ترسیم شد. یافتهها نشان داد که مقدار تنفس پایه و تحریک شده با بستره در زمینهای جنگلی با میانگین 1.24، به طور قابل توجهی بیش از زمینهای مرتعی و کشاورزی بود. در بین دو کاربری مرتعی و کشاورزی نیز مقدار تنفس میکروبی خاک در اراضی کشاورزی کمتر بود. اختلاف میانگین معنیدار در سطح آماری پنج و یک درصد به ترتیب بین تنفس میکروبی پایه و تحریک شده با بستره، در جهتهای شمالی و جنوبی شیب مشاهده شد. دامنههای جنوبی با دریافت بیشتر پرتوهای خورشیدی و کاهش رطوبت خاک، تنفس میکروبی پایینتری نسبت به دامنههای شمالی داشت. با افزایش ارتفاع به علت افزایش نسبی رطوبت هوا و کاهش دما، میزان تنفس میکروبی افزایش یافت. نتایج نشان داد که بین تنفس میکروبی خاک و ویژگیهای فیزیکی و شیمیایی آن همبستگی معنیداری وجود دارد. در مطالعه حاضر بین ویژگیهای درصد کربن آلی خاک، تخلخل، سیلت، رطوبت مزرعه و pH خاک با تنفس میکروبی پایه و تنفس تحریکشده با بستره، همبستگی بالایی مشاهده شد. همچنین مشاهده شد که روش درونیابی کریجینگ، از کارایی لازم برای تعیین نقشه پراکندگی مکانی تنفس میکروبی خاک برخوردار است. همبستگی بین برآورد انجام شده با کریجینگ و مقادیر اندازهگیری شده، در نقاط نمونهبرداری بیش از 0.2 و در سطح پنج درصد معنیدار بود.
1- Introduction
Spatial changes in soil properties are significantly influenced by factors affecting soil formation such as topography. Topography can create different properties in the soil by affecting the spatial distribution of effective environmental parameters. Topographic features such as contour, slope direction by affecting soil temperature, evaporation capacity, soil moisture, soil organic matter, precipitation, movement and accumulation of soil solution can affect the biological properties of soil. Respiration of soil microorganisms is one of the most sensitive and important biological properties that can affect soil quality. To study the impact of land use change on soil ecosystem performance due to human activities, it is necessary to maintain and restore soil capacity to provide ecosystem services. The aim of this study was to investigate the effect of slope and height classes on soil microbial respiration in agricultural, rangeland and forest areas of Khanghah Namin village.
2- Methodology
In order to conduct this research, in the fall, samples of intact and untouched soil from the study area were prepared in 72 points by regular networking method with distances of about 200 meters. Common physical and chemical properties of soil including soil pH, electrical conductivity, equivalent total calcium carbonate, organic matter, soil texture (percentage of sand, silt and clay particles) and total porosity were measured. From soil biomarkers, basal microbial respiration and substrate-stimulated respiration were determined. Kriging geo statistical method was used to estimate and determine the spatial distribution and evaluate some soil properties as well as cumulative soil quality indicators. For this purpose, the geographical coordinates of each point of the GPS device were transferred to GIS software. After recording the data of the sampled points, the interpolation command was executed and the information of the non-sampled points was obtained. In order to explain the spatial similarity of the variables, the experimental variogram of the data was obtained using GS + statistical software and the best variogram model was selected according to the variogram information. Finally, the distribution map of soil biological indicators was extracted using GIS and Kriging geo statistical methods. The correlation between the measured and estimated values of soil biological properties was calculated and evaluated in SPSS19 statistical software. Experimental factors included three land uses (namely, agriculture, rangeland and forest), slope direction at two levels (north and south) and two elevations (
3- Results
The results of the descriptive statistics of the soil properties showed that most of the soils in the study area have a loam soil texture class. The pH value of the samples was in the range of 5.7.7, the percentage of organic carbon was 0.6.6 % and calcium carbonate value was from 0.67 % to 16.67 %. The maximum electrical conductivity (EC) was less than 2 ds/m of Siemens per meter, indicating the non-saline soils of the area. Also, the high levels of average microbial base respiratory and the substrate induced respiration were 1.21 and 7.5, respectively. High correlation between the properties of soil organic carbon percentage, porosity percentage, silt percentage, farm moisture percentage and soil pH with base microbial respiration and substrate induced respiration with clay, sand and electrical conductivity of the soil were not significant. The farm moisture had the highest hydraulic soil with the lowest correlation with microbial respiration. In general, the average base and substrate induced respiration was higher on the height contour (1580by the Kriging internalization method.
4- Discussion & Conclusions
In this study, the amount of basal and bed-stimulated respiration in forest lands was significantly higher than rangeland and agricultural lands. Between rangeland and agricultural uses, the amount of soil microbial respiration in agricultural lands was lower. Due to the fact that this area is a tourist destination and there are local livestock, this finding can be attributed to transportation, high human and livestock activity at lower altitudes, and agricultural and pasture use, which are more exposed to these activities. The microbial respiration values in the northern direction of the slope were significantly higher than in the southern direction. The southern slopes received more solar energy than the northern slopes. Usually in the south-facing slopes, the number and activity of soil microbial community is low due to high temperature, low water, low porosity and adverse consequences due to inadequate vegetation. In addition, a significant mean difference was observed in the northern and southern directions of the slope. Also, the increase in altitude due to the relative increase in humidity and decrease in temperature led to an increase in microbial respiration. This issue can significantly affect the activity and respiration of soil microorganisms by affecting soil processes and its development as well as the amount of vegetation in the two slopes. According to the obtained results, it can be stated that the evaluation of biological properties that was discussed can play a prominent role in controlling the management factors in the area. Large changes in soil respiration indices are probably due to the high sensitivity of these properties to human factors such as tillage operations and the use of chemical fertilizers, which cause changes in soil surface uniformity. The zoning map of these two features also confirmed this. The results showed a logical correlation between soil microbial respiration and other characteristics that the existence of a correlation between soil properties indicates a strong relationship between them. Geo-statistical science in this study was able to estimate the properties well. The results of this study showed that in the studied area, biological indicators depend on the position of the landscape and land use, and these factors can affect the structure, development and evolution of soil by affecting the structure of the microbial community.