دانشگاه محقق اردبیلی مدل سازی و مدیریت آب و خاک 2783-2546 6 1 2026 03 21 Effect of Haloxylon plantation age on soil carbon and nitrogen stocks: management implications for arid land restoration تأثیر سن تاغ‌کاری بر ذخایر کربن و نیتروژن خاک: پیامدهای مدیریتی برای احیای اراضی خشک 287 302 4231 10.22098/mmws.2025.18631.1706 FA مرتضی صابری دانشیار گروه مرتع و آبخیزداری، دانشکده آب و خاک، دانشگاه زابل، زابل، ایران محمدرضا دهمرده قلعه نو دانشیار گروه مرتع و آبخیزداری، دانشکده آب و خاک، دانشگاه زابل، زابل، ایران وحید کریمیان استادیار گروه مهندسی طبیعت، دانشکده منابع طبیعی، دانشگاه یاسوج. یاسوج، ایران Journal Article 2025 10 21 <strong>Introduction</strong><br />The Iranian plateau, especially in arid and semi-arid regions, has sensitive and fragile conditions due to its specific climatic characteristics. In these regions, soil erosion and desertification are among the most important factors that severely threaten water and soil resources. In such conditions, the restoration of degraded rangelands through revegetation with compatible species such as Haloxylon spp<strong>.</strong> can play an effective role in reducing soil erosion, improving soil quality, and increasing carbon and nitrogen stocks. Due to its high resistance to drought and salinity, this species is one of the key options for stabilizing mobile sands and restoring desert ecosystems in Iran. In addition to its ecological role, the establishment of Haloxylon not only helps to increase soil organic carbon content and reduce atmospheric carbon dioxide but also can strengthen the livelihoods of local communities by improving soil conditions and providing economic opportunities. However, the dynamics of carbon and nitrogen stocks over time and with increasing plantation age are still not fully understood and require careful scientific investigation. Therefore, the present study aimed to investigate the effect of Haloxylon plantation age on soil carbon and nitrogen stocks in arid regions, to provide a basis for the optimal management of dryland restoration and the development of carbon sequestration schemes by explaining the relationships between soil properties and vegetation age.<br /><strong> </strong><br /><strong>Materials and Methods</strong><br />This study aimed to evaluate the effect of Haloxylon plantation age on soil carbon and nitrogen stocks in dry lands, in three areas located in the Merak area of Birjand County (South Khorasan province). The study areas included two Haloxylon plantations with ages of 34 and 26 years and a control area without Haloxylon cultivation, which are located about 10 km northeast of Birjand city. The altitude of the area varies between 1610 and 1810 meters above sea level, and its climate is dry and desert. Sampling operations were carried out in June 2024 using a systematic random method. In each area, six replicates were collected from three soil depths (0–15, 15–30, and 30–45 cm), and a total of 54 soil samples were used for physical and chemical analyses. Physicochemical properties, including pH, electrical conductivity, porosity, bulk density, organic carbon, and total nitrogen were measured, and soil carbon and nitrogen stocks were also determined. After checking for normality and homogeneity of variances, the resulting data were analyzed using a factorial design and one-way analysis of variance (ANOVA) in SPSS software. Also, the relationships between variables were examined using Pearson's correlation coefficient in R software.<br /><strong> </strong><br /><strong>Results and Discussion </strong><br />The results of the analysis of variance showed that the effects of both area (plantation age) and soil depth on physicochemical properties, including pH, electrical conductivity, bulk density, organic carbon, and total nitrogen were statistically significant (p<0.01). Comparison of means showed that with increasing age of the Haloxylon plantation, pH decreased slightly, and electrical conductivity was higher in the 26-year-old site. The decrease in bulk density and increase in soil porosity indicated improved soil structure and greater activity of roots and soil organisms. One-way analysis of variance of carbon and nitrogen stocks at each depth showed that these variables were significantly higher in the 34- and 26-year-old Haloxylon plantation sites than in the control area. The age of Haloxylon planting had a significant effect on soil carbon and nitrogen accumulation, with this effect varying by soil depth. In the 0–15 cm layer, the highest carbon stocks were observed in the 26-year-old site (4.46 t ha⁻¹), while in the 15–30 and 30–45 cm layers, the 34-year-old site exhibited the highest stocks (5.78 and 3.35 t ha⁻¹, respectively), indicating the role of vegetation growth stage and microbial activity in organic matter accumulation and stabilization, and highlighting the importance of long-term management and drought-resistant species in enhancing soil nutrient storage capacity. Principal component analysis (PCA) and correlation coefficients also showed that organic carbon, total nitrogen, and nutrient stocks are co-directional and correlated with each other, while bulk density has an inverse relationship. These findings emphasize that over time, Haloxylon<strong> </strong>cultivation improves the physical and chemical quality of the soil and increases the nutrient storage capacity and environmental sustainability of the soil in the drylands of the Merak region of Birjand County.<br /><strong> </strong><br /><strong>Conclusion</strong><br />The findings of this study indicate that the age of Haloxylon plantation plays a decisive role in improving soil quality and increasing carbon and nitrogen stocks in the drylands of Birjand County. Over time, the gradual accumulation of carbon and nitrogen in the surface and subsurface soil layers increased, and bulk density decreased, indicating improved soil structure, increased porosity, and higher activity of roots and soil microorganisms. Principal component analysis and correlation coefficients confirmed that increased soil organic matter is the main driver of the simultaneous increase in carbon and nitrogen stocks, and that the surface layers show the greatest sensitivity to management changes. These results indicate that long-term Haloxylon plantation can enhance soil ecological processes, including carbon and nitrogen cycling, and increase the environmental sustainability of drylands. From a management perspective, the results of the study indicate that selecting appropriate areas for Haloxylon plantation and continuously monitoring the age of vegetation cover can help increase soil fertility and improve nutrient storage capacity. Therefore, Haloxylon plantation is not only a soil restoration strategy, but with proper management, it plays an important role in the sustainable development of drylands. اراضی خشک و نیمه‌خشک ایران به دلیل محدودیت منابع آب و شرایط اقلیمی حساس، در معرض فرسایش خاک و کاهش حاصل‌خیزی قرار دارند. استفاده از گونه‌های مقاوم مانند زرد تاغ (<em>Haloxylon persicum</em>) برای تثبیت خاک و بهبود کیفیت آن، به‌ویژه از نظر ذخایر کربن و نیتروژن، اهمیت اکولوژیکی و مدیریتی دارد. این پژوهش با هدف بررسی تأثیر سن تاغ‌کاری بر ویژگی‌های فیزیکوشیمیایی خاک و ذخایر کربن و نیتروژن در شهرستان بیرجند انجام شد. بدین منظور، سه منطقه شامل دو تاغ‌زار با قدمت‌های ۳۴ و ۲۶ سال و یک منطقه شاهد (فاقد تاغ‌کاری) مورد بررسی قرار گرفتند. در هرسایت، با استفاده از روش نمونه‌برداری تصادفی<strong> </strong>سیستماتیک تعداد ۶ نمونه خاک از سه عمق صفر تا ۱۵، ۱۵ تا ۳۰ و ۳۰ تا ۴۵ سانتی‌متر برداشت گردید. نمونه‌ها پس از انتقال به آزمایشگاه، جهت اندازه‌گیری ویژگی‌های فیزیکوشیمیایی شامل pH<strong>، </strong>EC<strong>، </strong>وزن<strong> </strong>مخصوص ظاهری، تخلخل،<strong> </strong>کربن آلی و نیتروژن کل و همچنین تعیین ذخایر کربن و نیتروژن خاک مورد تجزیه و تحلیل قرار گرفتند. سن تاغ‌کاری اثر قابل‌توجهی بر تجمع کربن و نیتروژن خاک دارد و این اثر بسته به عمق متفاوت است، در عمق ۰-۱۵ سانتی‌متر بیشترین ذخایر کربن در سایت ۲۶ ساله (۴۶/۴) و در عمق‌های ۱۵-۳۰ و ۴۵-۳۰ سانتی‌متر در سایت ۳۴ ساله (۷۸/۵ و ۳۵/۳) مشاهده شد، که نشان‌دهنده نقش مرحله رشد پوشش و فعالیت میکروبی در تجمع و تثبیت مواد آلی است و اهمیت مدیریت طولانی‌مدت و گونه‌های مقاوم به خشکی برای افزایش ظرفیت ذخیره عناصر غذایی را برجسته می‌کند. کاهش وزن مخصوص و افزایش تخلخل نشان‌دهنده بهبود ساختار خاک و فعالیت بیشتر ریشه‌ها و میکروارگانیسم‌ها است. تحلیل مؤلفه‌های اصلی و همبستگی‌ها نشان داد که کربن آلی و نیتروژن کل هم‌جهت بوده و همبستگی بالایی با ذخایر عناصر غذایی دارند، در حالی که تراکم خاک رابطه معکوس با آن‌ها دارد. یافته‌ها تأکید می‌کنند که تاغ‌کاری بلندمدت موجب بهبود کیفیت فیزیکی و شیمیایی خاک، تقویت چرخه کربن و نیتروژن و افزایش پایداری اکولوژیکی اراضی خشک می‌شود. از منظر مدیریتی، انتخاب مناطق مناسب و پایش مستمر سن پوشش گیاهی، کلید ارتقای حاصل‌خیزی خاک و ظرفیت ذخیره عناصر غذایی و تضمین موفقیت برنامه‌های احیای اراضی خشک است. https://mmws.uma.ac.ir/article_4231_9a59be0919386c6df1c3d4b91163932c.pdf