بررسی تاثیر جهت و موقعیت شیب بر برخی شاخص های میکروبی خاک در زمین های مرتعی و جنگلی

ﻣﻄﺎﻟﻌﻪ ی ﺷﺎﺧصﻫﺎی ﮐﯿﻔﯿﺖ ﺧﺎک در کاربری های متفاوت و ﺑﺮ روی ﺑﺨﺶ ﻫﺎی مختلف زمین های شیب دار و انتخاب و به ‌کارگیری شاخص های مناسب، امکان مدیریت و استفاده‌ ی بهینه از خاک را میسر می‌ سازد. به‌ منظور بررسی تاثیر جهت و موقعیت شیب بر شاخص ‌های میکروبی خاک در زمین ‌های مرتعی و جنگلی،یک مطالعه به صورت فاکتوریل در قالب طرح کاملاً تصادفی با سه فاکتور کاربری اراضی در دو سطح (مرتع و جنگل)، جهت شیب در دو سطح (شمالی و جنوبی) و موقعیت شیب در سه سطح (شانه، پا و پنجه شیب) و با چهار تکرار در گردنه ی حیران، از توابع شهرستان آستارا در استان گیلان به اجرا درآمد. برای انجام این مطالعه، تعداد 48 نمونه خاک دست خورده از زمین های مرتعی و جنگلی از دو جهت شمالی و جنوبی شیب و در سه موقعیت شانه، پا و پنجه شیب تهیه و جمعیت میکروارگانیسم ‌ها، تنفس میکروبی پایه و تنفس ناشی از بستره، کربن زیتوده میکروبی و سهم میکروبی در آنها اندازه گیری شد. یافته ها نشان داد که مقدار تمام پارامترهای زیستی اندازه‌ گیری شده در خاکِ با کاربری جنگل، به‌ طور معنی ‌داری بیش از خاک با کاربری مرتع بود. در هر دو کاربری و در تمام موقعیت ‌های شیب، بیشترین مقدار تنفس میکروبی پایه و تنفس ناشی از بستره، جمعیت میکروارگانیسم‌ ها و کربن زیتوده میکروبی در شیب جهت شمالی اندازه ‌گیری شد. در کاربری ‌ها و جهت‌ های شیب مورد بررسی، تمام شاخص های زیستی به جزء سهم میکروبی در موقعیت شانه شیب بالاترین مقدار را داشتند. بیشترین مقدار سهم میکروبی (mgcmic.g1corg1.95) به شانه شیب در جهت شمالی بازمی گشت که با مقدار این شاخص در موقعیت های پا و پنجه شیب واقع در جهت شمالی، همچنین شانه و پنجه شیب در جهت جنوبی اختلاف معنی داری نداشت. همبستگی بین تمام شاخص ‌های زیستی در سطح احتمال یک درصد، خطی مثبت و معنی ‌دار بود. بالاترین همبستگی بین تنفس میکروبی پایه و تنفس ناشی از بستره (**94/.=r) و همچنین کربن زیتوده میکروبی و تنفس ناشی از بستره (**89/.=r) مشاهده شد.

Assessment the effect of Slope aspect and position on some soil microbial indices in rangeland and forest

Extended abstract Introduction Topography is one of the effective factors in soil formation and development. Topographical features such as slope aspect and position, by affecting soil temperature, evaporation capacity, soil moisture content, soil organic matter, precipitation, movement, and accumulation of soil solution can impress soil microbial properties. For investigating the effect of landuse change on soil ecosystem functioning because of human activities, it is essential to study the soil processes in disparate landuse systems and to preserve and regenerate the capability of soil to deliver ecosystem services. This study aimed at evaluating the effect of slope aspect and position on soil microbial indices in rangeland and forest areas of Heyran neck. MethodologyThis experiment was accomplished as factorial on the basis of a randomized complete block design with three treatments containing land use (forest and rangeland), slope aspects (north and south), and three slope positions (shoulder, footslope, toeslope), and four repetitions in Heyran neck, one of the functions of Astara city in Guilan province. Totally, 48 disturbed soil samples were taken from forest and rangeland at two aspects and three slope positions. From soil biological indices, soil microbial population, soil basal, and substrateinduced respiration (BR and SIR), microbial biomass carbon (MBC), and microbial quotient (qmic ) were measured. Soil microbial population was determined by the most probable number method (MPN method). The basal soil respiration was determined by placing 50g of soil in glass jars together with 10mL 0.05N NaOH in 20mL glass vials. All samples were incubated for 24h at 25 ± 1 oC, and the CO2 that evolved and was trapped during the period was determined by titration of the NaOH with 0.1N HCl. Substrateinduced respiration was determined by measuring the CO2 production from 50gr fresh soil. The soil samples included 1% glucose, were first placed in a glass jar. Then, an absorption bottle that was filled with 25ml of 0.1N NaOH was carefully put in the glass jar, and the glass jar was precisely sealed. The jar was then incubated at 25 ± 1 oC for 6h. The evolved CO2 was trapped by NaOH and determined by titration of NaOH with 0.1N HCL. Microbial biomass carbon was estimated by the chloroform fumigation and extraction method. Microbial quotient was calculated by dividing microbial biomass carbon (MBC) with soil organic carbon (SOC). Data rsquo;s normality was assessed through Kolmogorov -Smirnov test. The analysis of variance and comparison of means by Duncan test and Pearson correlations were done using SPSS software. Figures were prepared using Excel software. 3Results DiscussionThe results showed that the content of all biological parameters measured in the forest soils was significantly higher than in the rangeland soils. In both land uses and in all slope positions, the highest values of basal soil and substrateinduced respiration, microbial population, and microbial biomass carbon were measured in the northfacing slope. In the studied land uses and slope aspects, all biological indicators except the microbial quotient had the highest value in the shoulder position. In the southfacing slope, the content of microbial quotient in the toeslope position was measured more than in other positions. Still, there was no significant difference from the value of this index in the shoulder position. The highest value of microbial quotient (1.95 mgCmic.g1Corg) was observed in the northfacing slope on the shoulder, which was not significantly different from the value of this index in the footslope and toeslope positions of northfacing slope and also the shoulder and toeslope of southfacing slope. In forest land use, the content of microbial quotient in both northfacing (1.91 mgCmic.g1Corg) and southfacing (1.9 mgCmic.g1Corg) slopes was almost equal, which was significantly different from its value in both slope aspect of rangeland. The correlation between all biological indices at the level of one percent probability was positive and significant. There was the highest correlation between basal soil and substrateinduced respiration (r=0.94**) as well as microbial biomass carbon and substrateinduced respiration (r =0. 89**). 4 ConclusionsOverall, the results of this study showed that biological indices are dependent largely on landscape and land use, and by affecting the structure of the microbial community, these factors can affect the properties of the soil and its development. Due to the significant role of microorganisms as an integral component in the soil ecosystem and the effect of this component on the physical, chemical and nutritional properties of this ecosystem, by providing suitable conditions for the good activity of these organisms, soil quality can be increased, and thus erosion will be reduced.