Document Type : Research Article
Authors
1
Rangeland and Watershed Management Department, Faculty of Water and Soil, University of Zabol, Zabol, Iran
2
Department of Desert Areas Management, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran
Abstract
This paper assessed the influence of Haloxylon Persicum plantation age on soil physical, chemical, and microbial properties in the arid ecosystems of Birjand County, South Khorasan Province, Iran. Soil sampling was conducted at three sites: two planted sites (34 and 26 years old) and one unplanted control site. Physicochemical properties, including Soil Organic Carbon (SOC), Total Nitrogen (TN), available phosphorus and potassium, pH, EC, CaCO3 content, Sodium Adsorption Ratio (SAR), bulk density, and porosity, were measured. Microbial activity, Microbial Biomass Carbon (MBC) and Nitrogen (MBN), basal and substrate-induced respiration (SIR), and catalase enzyme activity were also evaluated. The results showed that with increasing plantation age, SOC and TN increased significantly, while bulk density decreased and porosity increased, indicating an improvement in soil structure, permeability, and ventilation, as well as enhanced microbial activity. Enzyme activity, microbial biomass, and microbial population also increased significantly in older sites, while the C/N ratio and Microbial Quotient (Qmic) remained statistically unchanged, indicating the maintenance of the functional balance of the microbial community. The positive correlation of SOC and TN with microbial indices, alongside the negative correlation of the C/N ratio, bulk density, and CaCO3 content, highlights the importance of physicochemical properties in determining soil health. These results indicate that long-term Haloxylon afforestation enhances soil quality, microbial activity, and the ecological capacity of desert ecosystems, providing a solid foundation for sustainable soil management and dryland restoration.
Introduction
Desertification, the most severe form of land degradation in arid and semi-arid regions worldwide, leads to a decline in biodiversity, reduced ecosystem stability, and detrimental alterations in ecosystem structure and function. Vegetation restoration, particularly using resilient native species such as Haloxylon persicum, is recognized as a highly effective strategy to combat desertification and restore local habitats. Soil microbial communities play a critical role in maintaining the stability and functionality of these arid ecosystems, especially through their key involvement in carbon and nitrogen cycling. However, comprehensive data on the changes in soil physical, chemical, and microbial properties across a gradient of Haloxylon plantation ages remain limited. This is particularly true in arid regions of eastern Iran, such as Birjand, where the long-term influence of native afforestation on soil structure and biological function has yet to be fully elucidated. The present study was designed to investigate the dynamics of the soil microbial community at various plantation ages and analyze their relationships with soil physicochemical properties. Its novelty lies in the integrated, multifaceted assessment of soil properties and microbial communities throughout different stand ages. This approach facilitates a deeper understanding of the plant-soil-microbe interactions and helps identify mechanisms influencing long-term ecosystem restoration. The results are expected to provide practical information for optimizing afforestation schemes, enhancing the resilience of arid ecosystems, and establishing a robust scientific basis for sustainable land restoration strategies.
Material and Methods
To investigate the effect of plantation age on the dynamics of the soil microbial community, this study was conducted in three distinct sites: two plantations aged 34 and 26 years, along with one unplanted control area, in the Merak region of Birjand city (South Khorasan province). Sampling was carried out in June 2025 using a systematic random method, with six sampling points selected as replicates at each site. At each replicate, soil samples were collected from a depth of 0 to 30 cm after removing the surface litter and transported separately to the laboratory. The physicochemical properties of the soil including Soil Organic Carbon (SOC), Total Nitrogen (TN), available phosphorus and potassium, pH, Electrical Conductivity (EC), porosity, bulk density, calcium carbonate content (CaCO3), and Sodium Adsorption Ratio (SAR) were measured. Soil microbial characteristics were assessed using standard methods, including catalase enzyme activity, basal and substrate-induced respiration (SIR), Microbial Biomass Carbon (MBC) and Nitrogen (MBN), and microorganism population (MPN). The Microbial Quotient (Qmic) was calculated as the ratio of MBC to SOC. After verifying normality and homogeneity of variances, the data were analyzed using one-way analysis of variance (ANOVA) within a completely randomized design. Relationships between physicochemical and microbial parameters were examined using Principal Component Analysis (PCA) and Pearson correlation coefficients in R software.
Results and Discussion
The results of this study showed that long-term Haloxylon afforestation significantly affects the physicochemical and microbial properties of soil in the arid ecosystems of the Birjand region. Analysis of variance revealed a significant impact of Haloxylon plantation on indicators such as SOC, TN, available potassium, pH, EC, CaCO3, SAR, bulk density, and porosity, while available phosphorus showed no significant change. Increasing the age of the Haloxylon stand was associated with a significant increase in organic carbon (1.73 to 18.7 g/kg) and more than a fourfold increase in total nitrogen compared to the control site. This indicates the substantial accumulation of organic matter, development of a robust root system, and enhancement of soil microbial activity. The decrease in bulk density and corresponding increase in porosity suggest improvements in soil structure, water permeability, and aeration. Changes in pH, EC, CaCO3, and SAR reflect adjustments in soil salinity and sodicity over time due to plant presence. Regarding microbial properties, catalase enzyme activity, basal and SIR, as well as MBC and MBN, increased significantly with the age of the Haloxylon plantation, indicating enhanced metabolic and ecological capacity of the soil. Microbial population and diversity improved in older cultivation sites, while the C/N ratio and the Microbial Quotient (Qmic) remained relatively stable, suggesting the maintenance of a functional balance within the microbial community. Positive correlations between SOC and TN with microbial indices, alongside negative correlations of the C/N ratio, bulk density, and CaCO3 content with microbial activity, underscore the importance of these physicochemical indices in determining overall soil health and biological performance. These findings emphasize that long-term Haloxylon afforestation improves soil fertility, promotes microbial activity, and increases the ecological stability of dry ecosystems, playing a key role in soil stabilization and improving its biological performance.
Conclusion
The results of this study showed that long-term Haloxylon afforestation in the arid ecosystems of Birjand has a significant and positive effect on the physical, chemical, and microbial properties of the soil. With increasing stand age, total SOC and TN increased significantly, indicating the substantial accumulation of organic matter from litterfall, root activity, and enhanced microbial turnover. The decrease in bulk density and increase in porosity demonstrate the improvement of soil structure, permeability, and the creation of suitable habitat conditions for microbial growth. Physicochemical changes, including the adjustment of soil salinity and sodicity and the reduction of CaCO3 content and SAR, highlight the positive long-term effects of Haloxylon afforestation on overall soil quality. Microbial indicators such as catalase enzyme activity, basal and SIR, as well as MBC and MBN also increase with the age of the Haloxylon plantation, demonstrating enhanced metabolic and ecological capacity of the soil. The population and diversity of microorganisms in older Haloxylon persicum stands improved, while the carbon-to-nitrogen ratio and Qmic remained stable, suggesting the maintenance of functional balance within the microbial community. The positive correlation of SOC and TN with microbial indices and the negative correlation of C/N ratio, bulk density, and CaCO3 with microbial activity highlights the critical role of physicochemical properties in soil health. PCA analysis identified the first axis as the main factor separating the sites, with SOC, TN, and MBC contributing the most to explaining the observed differences. These findings indicate that long-term Haloxylon afforestation enhances soil quality, microbial activity, and the ecological capacity of desert ecosystems, providing valuable insights for sustainable soil management and restoration.
Acknowledgements
The authors gratefully acknowledge the financial support of the University of Zabol (Grant code: IR-UOZ-GR-8721) for conducting this research.
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