وضعیت ماده آلی خاک در توده های جنگلی ارسباران

با توجه به نقش های مهم ماده آلی خاک در اکوسیستم، ضروری است که وضعیت آن در شرایط مختلف محیطی مورد بررسی قرار گیرد. بر این اساس مطالعه حاضر در زیر حوضه کلیبرچای سفلی از جنگل های ارسباران با مطالعه پنج خاکرخ شاهد در بخش های محیطی متمایز شده برمبنای توزیع تیپ های جنگلی در امتداد یک نیمرخ ارتفاعی انجام شد. ضمن تجزیه های مرسوم خاک، شناسایی نوع آن و مطالعه وضعیت ماده آلی، به عنوان هدف اصلی تحقیق، با بررسی مقدار ماده آلی خاک، توان ترسیب کربن آلی آن و مطالعه میکرومرفولوژیک شکل های بقایای آلی تکمیل گردید. نتایج بیان گر تغییر نوع خاک از انتی سول، اینسپتی سول و آلفی سول به مالی سول با کاهش ارتفاع بود. در روندی مشابه، همگام با افزایش تکامل خاک میزان ترسیب کربن آلی آن نیز افزایش یافت امّا مقدار ماده آلی روندی عکس به دلیل نوع فرآیندهای دخیل در تجزیه بقایا در نواحی مختلف نشان داد. با توجه به امکان روی دادن انواع فرآیندهای فیزیکی و بیوشیمیایی تحت شرایط مختلف محیطی، در نواحی مرتفع شکل های دست نخوررده بقایای آلی به عنوان شکل غالب شناخته شدند امّا با کاهش ارتفاع غالبیت در اختیار شکل های کاملاً تجزیه شده بود. در محدوده و مقیاس مورد مطالعه عامل ارتفاع با توجه به اثرات مستقیم و غیرمستقیم خود به عنوان اصلی ترین فاکتور محیطی کنترل کننده وضعیت ماده آلی خاک تشخیص داده شد. در نهایت نتیجه شد با توجه به ارتباط بین نوع خاک، مقدار ماده آلی، توان ترسیب کربن آلی خاک و شکل های بقایای آلی می توان از شناسایی خاک ها و توزیع آن ها در مدیریت منطقه ای کربن آلی خاک نیز استفاده نمود.

Soil Organic Matter Condition in Forest Stands of Arasbaran

،Introduction: According to important ecological roles of soil organic matter in stabilizing ecosystems, it is essential to consider soil organic carbon condition for managements of worldwide problems such as soil quality, carbon cycle and climate change. Also, organic matter is one of the main component of soil which have vital impress on its evolution. Therefore, assessing soil organic matter fate in various environmental conditions and its relation with environmental factors will be useful for management decisions. Determining soil organic carbon content, stocks and forms by the physicochemical and micromorphological studies may respond to the question about soil organic matter evolution from the different point of views. Based on mentioned reasons, our research work focused on soil organic matter content, stocks and forms under various environmental condition of the forest ecosystem to find new aspects of its relation with environmental factors.،Material and Methods: This research work was carried out in Arasbaran forest, northwest of Iran, which recognized as a part of the international network of biosphere reserves and has unique species of plants with special ecological properties. Sampling was carried out in a Kaleybar Chai Sofla subbasin as a part of Arasbaran forest with eastern longitude of 46º 39´ to 46º 52´ and northern latitude of 38º 52´ to 39º 04´. Based on the Amberje climate classification, the climate of the region is semihumid and moderate. The soil moisture and temperature regimes are Xeric and Mesic, respectively. Hornbeam (Carpinus betulus) and Oak (Quercus petraea and Quercus macranthera) were identified as the main woody species in this area and volcanosedimentary rocks were the geological structure. Primary site surveying showed 5 forest stand types such as Oak (Quercus macranthera), HornbeamOak (Carpinus betulusQuercus macranthera), Hornbeam (Carpinus betulus), HornbeamOak (Carpinus betulusQuercus petraea), Oak (Quercus petraea) along altitudinal transects, that used as environmental parts with different conditions. In each environmental part, a soil profile was described and sampling was done for physical, chemical and micromorphological analysis. After preparing soil samples in the laboratory, soil physicochemical routine analyses were carried out by standard methods and then the studied soils were classified on the basis of 12th edition of soil taxonomy. To achieve the main aim of the study, various aspects of soil organic matter evolution were assessed. Soil organic matter content was determined according to the Walkley–Black wet oxidation method and using alteration factor f = 1.724 recommended by USDA. Variance analysis and means compare of soil organic matter content in surface horizons of different environmental parts were performed by using the SPSS software package and Dunkan apos،s multiple range test, respectively. Soil organic carbon stocks were calculated for each soil horizon and weighted average based on profile depth was used to calculate this index for each soil profile. The prepared thin section for micromorphological study was examined under both planepolarized light (PPL) and crosspolarized light (XPL) using a polarized microscope and explained based on standard terminology to identify various forms of soil organic matter all over the study area.،Results and Discussion: Results revealed increasing of soil evolution with decreasing of elevation. Entisols, Inceptisols, Alfisols and Mollisols with different families were the soil observed along altitudinal transects by decreasing elevation. According to the obtained results, environmental effects caused different soil organic matter content and evolution with various soil organic carbon stocks in each part. Improvement of environmental condition by decreasing elevation resulted in more evolution of soil organic matter, dominant of decomposed forms of organic matter and rise of soil organic carbon stocks from the highest part to the lowest one. Soil organic matter content in soil surface increased by elevation, although the main source of soil organic matter have better condition in lower parts due to ecological reasons. This inverse statue can be explained by special environmental conditions causing limited organic remnants decomposition in the highest parts. In the same trend with soil evolution, soil organic carbon stocks increased by decreasing of elevation. This trend refers to the relation of mentioned index ability with various soilforming processes. Micromorphological study showed that organic intact remnants were the dominant forms in upper parts which changed to welldecomposed forms in the lowest parts. This observation revealed the occurrence of mechanical decomposition processes of organic remnants in high elevation while biochemical ones happen in the lower parts. Also, this distribution of soil organic matter decomposition processes can explain soil organic carbon content and stocks all over the study area.،Conclusion: Elevation was identified as an important environmental factor controlling soil organic matter in the studied scale. Generally, results confirm the same trend for soil organic matter evolution and soil organic carbon stocks with soil development, especially in pedogenesis processes in relation to organic matter. Thus, it can be recommended to use soil map for management of soil organic matter under various environmental conditions in largescale studies.