کاربرد مدل RothC در شبیه‌سازی اثر تغییرات اقلیمی بر انتشار کربن دی‌اکسید و ذخایر کربن آلی خاک اقلیم نیمه‌خشک خراسان رضوی

نوع مقاله : مقالات پژوهشی

نویسندگان

• صبا باقریفام ¹
• محمد امیر دلاور ²
• پیمان کشاورز ³
• پرویز کرمی ⁴

¹ دانشجوی دکتری گروه علوم و مهندسی خاک، دانشکده کشاورزی، دانشگاه زنجان، زنجان، ایران

² دانشیار گروه علوم و مهندسی خاک، دانشکده کشاورزی، دانشگاه زنجان، زنجان، ایران.

³ دانشیار بخش تحقیقات خاک و آب، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی خراسان رضوی، مشهد، ایران.

⁴ استادیار گروه مهندسی مرتع و آبخیزداری، دانشکده منابع طبیعی، دانشگاه کردستان، سنندج، ایران.

10.22067/jsw.2022.78752.1202

چکیده

خاک با از دست دادن کربن به شکل کربن دی‌اکسید، پتانسیل زیادی برای تشدید گرمایش زیست‌کره دارد. از سوی دیگر امکان ترسیب کربن در خاک، راهکار مناسبی جهت کاهش انتشار کربن دی‌اکسید شناخته می‌شود. خاک‌های مناطق خشک و نیمه‌خشک جهان اگرچه حاوی مقادیر کمی کربن آلی هستند؛ اما به‌واسطه وسعت زیاد، امکان ترسیب مقادیر قابل‌توجهی کربن آلی را دارند. از این‌رو جهت بررسی تغییرات ذخایر کربن آلی خاک اراضی زراعی اقلیم نیمه‌خشک جلگه‌‌رخ واقع در استان خراسان رضوی، مدل رتامستد با استفاده از داده‌های مطالعات پیشین و مقادیر اندازه‌گیری شده در سال 2020 اعتبارسنجی شد. مقایسه بین مقادیر کربن آلی اندازه‌گیری شده و شبیه‌سازی‌شده توسط مدل، نشانگر قابلیت مدل در ارائه پیش‌بینی‌هایی با دقت مناسب بود. به‌طوری‌که مقادیر ضریب تبیین، ریشه میانگین مربعات خطا، میانگین مطلق خطا، تفاوت میانگین و شاخص کارایی مدل به ترتیب معادل 97/0، 78/2، 11/2، 33/2 و 70/0 به‌دست آمدند. سپس تأثیر تغییرات اقلیمی بر انتشار کربن دی‌اکسید و ذخایر کربن آلی خاک منطقه مدل‌سازی شد. بررسی تغییرات اقلیمی منطقه در (دوره آماری 1981 تا 2020) نشانگر کاهش بارندگی و افزایش معنی‌دار دما طی 40 سال گذشته بوده است. مدل‌سازی تغییرات اقلیمی تا پایان قرن جاری با اعمال افزایش دما و کاهش بارندگی انجام شد که نتایج بیانگر کاهش همه ذخایر کربن فعال مدل بود، چنان‌که مخازن مواد گیاهی تجزیه‌پذیر، مواد گیاهی مقاوم، زیست‌توده میکروبی، مواد آلی هوموسی‌شده و کل کربن آلی خاک به‌ترتیب معادل 41/2، 72/2، 51/2، 04/1 و 32/1 درصد نسبت به شرایط عدم وقوع تغییرات اقلیمی کاهش و میزان انتشار تجمعی کربن دی‌اکسید از خاک، 26/1 درصد افزایش نشان داد. افزایش دما باعث افزایش ضریب تصحیح دما (a) به میزان 20/2 درصد شد که منجر به افزایش سرعت تجزیه کربن آلی و تلفات کربن به شکل کربن دی‌اکسید شده است؛ اگرچه باعث افزایش تولید خالص اولیه بوم‌نظام نیز گردید. کاهش بارندگی و افزایش تبخیر و تعرق پتانسیل نیز باعث کاهش ضریب تصحیح رطوبت (b) به میزان 23/0 درصد شد؛ این فرایند از یک سو با کاهش فعالیت ریزجانداران موجب کاهش تجزیه زیستی کربن و انتشار کربن دی‌اکسید از خاک شده است؛ اما از سوی دیگر موجب کاهش درصد پوشش گیاهی و پیرو آن به دام انداختن کربن دی‌اکسید طی فرایند فتوسنتز و انتقال آن به خاک می‌گردد.

کلیدواژه‌ها

• تجزیه ماده آلی خاک
• ترسیب کربن
• شاخص کارایی
• گرمایش جهانی
• مدل رتامستد

20.1001.1.20084757.1401.36.5.6.6

موضوعات

• علوم خاک

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عنوان مقاله [English]

Application of the RothC Model in Simulating Effect of Climate Change on CO2 Emissions and Soil Organic Carbon Stocks in Semi-arid Climate of Khorasan-e-Razavi

نویسندگان [English]

• Saba Bagherifam ¹
• Mohammad Amir Delavar ²
• Payman Keshavarz ³
• Parviz Karami ⁴

¹ PhD student, Dept. of Soil Science, Faculty of Agriculture, University of Zanjan, Zanjan, Iran

² Associate Professor, Dept. of Soil Science, Faculty of Agriculture, University of Zanjan, Zanjan, Iran.

³ Associate Professor, Dept. of Soil and Water Research, Khorasan Razavi Agricultural and Natural Resources Research Center, AREEO. Mashhad, Iran.

⁴ . Assistant Professor, Dept. of Range and Watershed Management, Faculty of Natural Resources, University of Kurdistan, Sanandaj, Iran.

چکیده [English]

Introduction
 Soil is one of the main drivers of global warming through losing carbon in the form of CO₂. On the other hand, its ability to sequester carbon is a suitable option for reducing CO₂ emissions. Therefore, even few changes in carbon sequestration or decomposition of soil organic carbon affect the global atmospheric CO₂ content. Although the soils of arid and semi-arid regions have low organic carbon content, they can sequester substantial amounts of carbon due to the large area of these regions. So, the Rothamsted carbon model was used to predict the impact of future climate changes on the amount of CO₂ emissions and low soil organic carbon stocks in the semi-arid arable lands of Razavi Khorasan province. This model is one of the most widely used models for the study of soil organic carbon turnover and has been evaluated in a variety of ecosystems including grasslands, forests and croplands and in various climate regions. The RothC model is consists of five conceptual soil carbon pools, four active fractions and a small amount of inert organic matter (IOM) that is resistant to decay. The active pools splits into: Decomposable Plant Material (DPM), Resistant Plant Material (RPM), Microbial Biomass (BIO) and Humified Organic Matter (HUM). This model is able to reveal the effect of soil texture, temperature, rainfall, evaporation, vegetation and crop management on the soil organic carbon turnover process.
Materials and Methods
 The Rothamsted carbon model was calibrated and validated using data measured in 2020 and available data from the long-term field experiments in the semi-arid agricultural lands of Jolge Rokh. Then, by analyzing the climate change of the study area, the impact of climate change until the end of the current century on the amount of CO₂ cumulative emissions, total organic carbon (TOC) and active carbon pools model were modeled and compared in the current climate and also climate change conditions.
Results and Discussion
 The comparison between the measured and simulated soil organic carbon values by the model shows the potential of the model to provide predictions with acceptable accuracy. The outcome of comparisons revealed that R², Root Mean Square Error (RMSE), Mean Difference (MD), Mean Absolute Error (MAE) and Model efficiency were 0.97, 2.78, 2.11, 2.33 and 0.70 respectively. Assessment of climate changes in the region (during 1981-2020) showed a decrease in precipitation and a significant increase in temperature over the past 40 years. Climate change simulation was carried out by temperature increasing and decreasing the precipitation until the end of the current century, indicated the decrease of all active carbon pools. It was found that DPM, RPM, BIO, HUM and TOC decreased respectively to 2.41, 2.72, 2.51, 1.04 and 1.32% compared to the current climatic conditions, while the cumulative CO₂ emission increased by 1.26%. Temperature rising leads to increase the rate modifying factor (a) by 2.20%, which enhances microbial respiration and decomposition rate of organic carbon and CO₂ emissions (carbon output). However, it also increases the ecosystem's net primary productivity (carbon input). Decreases in rainfall and increase in potential evapotranspiration cause a reduction of the rate modifying factor (b) to 0.23%, which on one side reduces the activity of microorganisms and carbon biodegradation; but on the other side, it decreases the vegetation cover and following that reduces CO₂ trapping during the photosynthesis process and transfers it to the soil. It seems that in arid and semi-arid climates where the lack of moisture is the most important limiting factor of the plants growth; the role of precipitation in carbon decomposition and sequestration is greater than temperature.
Conclusion
 The Rothamsted carbon model is suitable for regional simulations because it requires only easily obtainable inputs. Therefore RothC is an appropriate tool for estimating long-term effects of climate change and agricultural management (such as application of manures, returning plant residues to the soil, crop rotations, conservation tillage etc.). The RothC model validation in the cold semi-arid agricultural lands of the region, shows the ability of model to properly simulate the pattern of organic carbon changes. Also, simulation of soil organic carbon changes under the climate changes conditions indicates an increase in cumulative CO₂ emissions and decrease in soil organic carbon pools of the study area. The methodology can be applied to other regional estimations, provided that the relevant data are available. The predictions allowed to identify the land management potential to carbon sequestration. Such information demonstrate a beneficial tool for evaluation of past land management effects on soil organic carbon trends and also estimation of future climate change effects on soil organic carbon stocks and CO₂ emissions.

کلیدواژه‌ها [English]

• Global warming
• Carbon sequestration
• Decomposition of soil organic matter
• Model efficiency
• Rothamsted carbon model

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