تأثیر پوشش های گیاهی و مدیریت زمین بر بخش های کربن آلی خاک در حوضه گنبد، همدان

نوع مقاله : مقالات پژوهشی

نویسندگان

1 دانشگاه بوعلی سینا همدان

2 مرکز تحقیقات کشاورزی و منابع طبیعی همدان

چکیده

کربن آلی خاک در اثر فرآیندهای چرخه ای نظیر ورود بقایای گیاهی و نوع پوشش گیاهی مستقر در آن دائماً در تغییر است. به منظور بررسی تآثیر پوشش های گیاهی مختلف بر بخش های کربن آلی خاک، پنج تیپ گیاهی مرتعی شامل گندمیان، گون-بروموس، گون-جارو، گون-درمنه و گون-فرفیون در زیرحوضه های شاهد و حفاظت شده ی حوضه گنبد، و یک تیپ زراعی (گندم دیم)، در شرایط محیطی مشابه از نظر اقلیم کلان، مواد مادری و جهت شیب در همدان مطالعه شد. کربن آلی کل، ذخیره کربن، ذخیره کربن اصلاح شده با شن، کربن فعال، کربن فعال اصلاح شده با کربن، کربوهیدرات، کربوهیدرات اصلاح شده با کربن، تنفس پایه و تنفس پایه اصلاح شده با کربن در دو فصل پاییز و بهار در لایه خاک سطحی (15-0 سانتی متر) اندازه گیری شد. کربن آلی، ذخیره کربن، کربوهیدرات و تنفس پایه در تیپ های گون-بروموس و گون-درمنه به طور معنی داری بیشتر از دیگر تیپ ها بودند و کمترین مقدار این شاخص ها در تیپ های گندمیان و گندم دیم مشاهده شد. بیشترین و کمترین مقدار کربن فعال به ترتیب در تیپ گون-بروموس و تیپ گندم دیم (به ترتیب 7/711 و 6/262 میلی گرم بر کیلوگرم) مشاهده شد. کربوهیدرات اصلاح شده در تیپ گون-فرفیون به طور معنی داری کمتر از همه تیپ ها بود. اثر فصل بر تمام شاخص ها، به غیر از کربن فعال اصلاح شده، کربوهیدرات و تنفس پایه معنی دار بود. مقدار کربوهیدرات اصلاح شده بر خلاف دیگر شاخص ها، به طور معنی داری در فصل پاییز بیشتر از فصل بهار بود. در کل، نوع پوشش گیاهی و مدیریت زمین بیشترین تأثیر را بر شاخص های ذخیره کربن، کربن فعال و کربوهیدرات نشان داد.

کلیدواژه‌ها


عنوان مقاله [English]

Influence of Vegetation Type and Land Management on Soil Organic Carbon Fractions in Gonbad Watershed, Hamadan

نویسندگان [English]

  • Khadije Salarinik 1
  • Mohsen Nael 1
  • Ghasem Assadian 2
  • Ali Akbar Safari Sinegani 1
1 Bu-Ali Sina University, Hamedan
2 Agricultural and Natural Research Center of Hamedan
چکیده [English]

Introduction: Soil organic matter is influenced strongly by vegetation cover and management, therefore it is proposed as the main indicator of soil quality and health. The changes in soil organic matter status occur much more rapidly in the labile pools than in organic C. Thus, labile pools can be used as early indicators of changes in total organic matter that will become more obvious in the longer term here. In addition, the labile fraction has a disproportionately large effect on nutrient-supplying capacity and structural stability of soils. Land management as well as soil and environmental conditions lead to the deployment of different plant communities in rangeland ecosystems, which in turn may have different effects on soil quality indicators. The main objective of this research was to investigate the influence of different vegetation covers on the quantity and quality of soil organic carbon fractions in Gonbad experimental watershed, Hamadan. Moreover, the seasonal changes of selected soil carbon fractions were investigated.
Materials and Methods: Paired Gonbad watershed in Hamedan consists of two sub-basins: in control sub-basin no grazing management is applied, while in protected sub-basin, grazing has been restricted to a very short period in late autumn since 2002. Average annual precipitation and average annual temperature in the area are 304.4 mm and 9.5 °C, respectively (5). The soil cover of the watershed consists of TypicCalcixerepts, TypicHaploxerepts and Lithic Xerorthents (9). Five different vegetation typesof which, grasses (G), Astragalus-Bromus (A-B), Astragalus-Artemisia (A-A), Astragalus-Lactuca (A-L) in protected sub-basin, and Astragalus-Euphorbia (A-E) in control sub-basin, were selected. In addition, a formerly cultivated hilly land outside the watershed, now under rainfed wheat farming (RW) was selected as a non-pasture vegetation type. All of the six vegetation types were similar in terms of soil parent materials and slope aspect.. Soil and plant sampling were conducted in mid-autumn 2012 (a), and late spring 2013 (s). Three plots (1*1 m2) were studied in each vegetation type. Total organic carbon (TOC), carbon stock (CS), carbon stock normalized with sand(CS/Sa), active carbon (AC), normalized active carbon (AC/TOC), soil carbohydrates (Ch), normalized carbohydrates (Ch/TOC), basal respiration (BR) and normalized basal respiration (BR/TOC) were measured in surface soils (0-15 cm). A factorial experimental design with two factors, vegetation type (6 levels) and time (2 levels), was conducted. Prior to statistical analysis, data were normalized, if required.
Results and Discussion: TOC and CS contentswere significantly different between vegetation types. A-B and A-A had highest canopy cover, litter cover and species diversity. Species diversity in the rangeland ecosystems has direct effect on fodder production and soil organic carbon content. A-E site, despite its low TOC content, hadhigher CS/Sa (51.9 Mg/ha) due to higher amount of clay content, compared to A-A (43.1Mg/ha) with higher TOC content. The amount of AC andAC/TOC in different vegetation types is proportional to the amount of TOC, CS, total canopy, and the canopy and production of herbaceous species. AC content was significantly highest in A-B (711.7 mg/kg), and lowest in RW site(262.6 mg/kg). A-B site is rich in grass species with high amounts of readily decomposable root residues and exudates. The variation of carbohydrate contents in different vegetation types wasvery similar to that of total organic carbon, in that A-B and A-A exhibited the highest (5843 and 5258 mg/kg, respectively) and RW showed the lowest (1937 mg/kg) carbohydrate contents. The woody, not easily decomposible litters in A-A explainedthe high content of Ch/TOC (38.12%) in this site; low rate of humification entails increased soil carbohydrates. Ch/TOC was significantly lower in A-E than other covers. The highest BR andBR/TOC, were observed in A-B and A-A sites, mainly due to the high canopy cover, species richness,and soil organic matter. The lowest BR andBR/TOC were observed in A-E.Thesoil texture in this site was clay.The recirculation of organic matter in fine-textured soils is low because of organic materials protection from microbial decomposition. Total organic matter and labile organic carbon inputs werelower in A-L, A-E and G sites; this may explain the reduction of microbial activity in these vegetation types. Except for AC/TOC, Ch, and BR, seasonal changes of all other indicators were significant. Unlike other indicators, the content of Ch/TOC was significantly higher in autumn than spring.
Conclusion: Vegetation types had significant effects on selected soil quality indicators, so that A-A and A-B sites exhibited the highest soil quality, mainly because of higher vegetation cover, litter, and plant diversity. RW, followed by A-E site, demonstrated the lowest soil quality due to the tillage practices and low plant residue inputs in the first case, and overgrazing of vegetation cover and litter in the second. Total soil organic carbon and active carbon were significantly higher in spring compared to autumn. Seasonal changes of basal microbial respiration and carbohydrates were not statistically significant.

کلیدواژه‌ها [English]

  • Active carbon
  • Basal respiration
  • Carbohydrate
  • Soil quality
  • Vegetation type
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