Climate-Scenario Impacts on Soil CO₂ Emissions across Four Afforestation Types and Their Understories in Meighan Desert

Document Type : Research Paper

Authors

1 Department of Rehabilitation of Arid and Mountainous Regions, Faculty of Natural Resources, University of Tehran 31587-77871, Tehran, Iran

2 Department of Rehabilitation of Arid and Mountainous Regions, Faculty of Natural Resources, University of Tehran, 31587-77871, Tehran, Iran

3 Department of Management of Desert Regions, International Desert Research Center, University of Tehran, Tehran, Iran.

Abstract

Objective: The primary aim of this study was to calibrate and validate the Rothamsted Carbon model (RothC) and to simulate the effects of future climate scenarios on soil respiration flux from Tamarix, Haloxylon, Atriplex, and Nitraria trees and their understory rangelands in the Meighan Kavir. Method: Following RothC model validation, the impacts of a baseline scenario without climate change and three projected climate scenarios (RCP2.6, RCP4.5, and RCP8.5) were simulated across three periods (2025–2040, 2041–2060, and 2061–2080) to estimate soil respiration fluxes from the different vegetation covers. Results: Model validation demonstrated high accuracy of RothC in reproducing observed SOC data in the Meighan Kavir, with a model performance efficiency (EF) of 0.96. Compared to the baseline scenario, the highest soil respiration fluxes were predicted in 2025–2040 under RCP4.5 and RCP8.5 (up to a 36% increase), and in 2041–2060 under RCP2.6 (up to a 30% increase). Across all vegetation types, soil respiration fluxes exhibited a decreasing trend over time under all climate scenarios. After 2061, the decline slowed and approached a relatively stable state, though minor variations among vegetation types persisted. Conclusions: Considering the lower soil respiration fluxes from Nitraria trees and their understory rangelands, combined with the species’ native status, Nitraria is recommended for cultivation and restoration in the Meighan Kavir to mitigate desertification.

Keywords

Main Subjects

Introduction

Climate change exerts a profound influence on soil organic carbon (SOC) dynamics; however, substantial uncertainties remain regarding its long-term effects on soil respiration flux in desert ecosystems. Although numerous biological restoration and rehabilitation initiatives have been implemented in the desert regions of Iran—particularly in the Meighan Kavir—no previous study has systematically quantified or modeled SOC dynamics and soil respiration flux at the ecosystem scale. In this study, the RothC model was employed to simulate SOC turnover and associated soil respiration fluxes under projected climate change scenarios, providing a robust assessment of the potential effectiveness of these restoration efforts in mitigating carbon losses in desert ecosystems.

Materials and Methods

The study was conducted in the Meighan Kavir, located northeast of Arak County (34°09′N, 49°55′E) in central Iran. At a mean elevation of 1,670 m a.s.l., this region represents one of the higher desert terrains in Iran. This research provides one of the earliest systematic evaluations of soil respiration flux under Iranian desert conditions, with the specific objectives of: (i) assessing the performance of the RothC model in simulating SOC dynamics in the Meighan Kavir; and (ii) quantifying the effects of eight different biological restoration projects on soil respiration flux under both current (1980–2024) and projected future climate scenarios (2025–2080), including RCP2.6, RCP4.5, and RCP8.5, across three periods (2025–2040, 2041–2060, and 2061–2080). The afforestation projects included Haloxylon, Tamarix, Atriplex, and Nitraria trees, along with their understory vegetation, all established within a flat basin physiography. By integrating RothC simulations with observed field data, this study provides a robust assessment of how restoration strategies influence SOC dynamics and soil respiration fluxes under changing climate conditions in desert ecosystems.

Results

Statistical comparisons between the simulated and observed SOC data, including the coefficient of determination (R² = 0.98), Pearson correlation (r = 0.99), RMSE% (6.85), and model efficiency (0.96), indicated that the RothC model accurately reproduced the observed SOC stocks. Simulations over a 56-year period (2025–2080) predicted that soil respiration fluxes would range between 0.322 and 0.874 Mg C ha⁻¹ under future climate change scenarios. The magnitude of the flux differed among vegetation types in the following descending order: Tamarix trees > Haloxylon trees > Atriplex trees > Atriplex understory > Haloxylon understory > Nitraria trees > Tamarix understory > Nitraria understory.

The model outputs further revealed that the highest soil respiration fluxes occurred in 2025–2040 under the RCP4.5 and RCP8.5 scenarios, and in 2041–2060 under the RCP2.6 scenario. Compared to the baseline scenario without climate change, soil respiration fluxes increased by 36% under RCP4.5 and RCP8.5 during 2025–2040, and by 30% under RCP2.6 during 2041–2060. The largest percentage changes were associated with tree vegetation, in descending order: Atriplex trees > Haloxylon trees > Nitraria trees > Tamarix trees, while understory vegetation showed nearly uniform flux changes.

Overall, soil respiration fluxes under all vegetation covers followed a decreasing trend over time, with a similar pattern across scenarios. After 2061, the rate of decline slowed substantially and reached a relatively stable state, although the near-constant flux still varied among vegetation types, following the same descending order as above.

Conclusion

Among tree vegetation covers, Tamarix trees exhibited the highest soil respiration fluxes, while Nitraria trees showed the lowest. For rangeland (understory) vegetation, the highest and lowest fluxes were observed for Atriplex and Nitraria, respectively. Considering its native status and minimal contribution to soil respiration flux, Nitraria is recommended as a suitable species for further cultivation and restoration efforts in the Meighan Kavir.

Overall, although soil respiration fluxes in the Meighan Kavir have increased due to climate change, projections indicate that with continued rises in temperature and further reductions in precipitation, fluxes are expected to gradually decline over time and eventually stabilize. This stabilization likely reflects the establishment of a new equilibrium in soil carbon pools, possibly due to humification processes and the inherent resistance of SOC to decomposition. Consequently, future research should focus on characterizing humus composition and dynamics in Meighan Kavir soils to better understand the long-term behavior of SOC under changing climatic conditions.

 

Highlights

We modeled SOC data with RothC model in eight vegetation covers

Soil CO2 emissions were evaluated under present and climate change scenarios

Climate change increased soil CO2 emissions by 2080

Soil CO2 emissions decreased over time

Funding

This study was performed under the umbrella of financial support of the Faculty of Natural Resources, University of Tehran, Tehran.

Author Contributions

Conceptualization, Bijan Azad, Hossein Azarnivand, Hamid Reza Naseri, and Gholam Reza Zehtabian.; Methodology, Bijan Azad, Hossein Azarnivand, Hamid Reza Naseri, and Gholam Reza Zehtabian; Software, Bijan Azad.; Validation, Bijan Azad, Hossein Azarnivand, and Hamid Reza Naseri.; Formal analysis, Bijan Azad; Investigation, Bijan Azad, Hossein Azarnivand, Hamid Reza Naseri, and Gholam Reza Zehtabian; Writing—original draft preparation, Bijan Azad.; Writing—review and editing, Hossein Azarnivand, Hamid Reza Naseri, and Gholam Reza Zehtabian.; Visualization, Bijan Azad.; Supervision, Hossein Azarnivand.; project administration, Bijan Azad. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

Data available on request from the authors.

Acknowledgements

Special thanks to Eng. M. Yazdanifar, Dr. S. Shamshiri, Eng. M. Akbari, Eng. M. Namdari, Mr. Khoshdoni, Eng. Rezaee, Eng. Abbas Nezhaz, Eng. Hashemi,  for field samplings. We thank the anonymous reviewers for their comments and suggestions.

Ethical considerations

The authors avoided data fabrication, falsification, plagiarism, and misconduct.

Conflict of interest

All authors declare that they have no conflict of interest.

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Iranian Journal of Soil and Water Research
Volume 56, Issue 12
March 2026
Pages 3393-3414

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