Evaluation of Floristic Diversity and Carbon Storage in Soil and Biomass of Dominant Rangeland Species and Their Role in Ecological Sustainability

Climate change and rising atmospheric carbon dioxide levels represent major environmental challenges, particularly for dryland ecosystems whose sustainability is increasingly at risk. Carbon sequestration in vegetation and soil—especially within rangelands—plays a crucial role in mitigating atmospheric carbon concentrations and improving soil health. This study aimed to document the flora of the Sarsaro rangelands and evaluate the carbon storage capacity of dominant plant species and their associated soils. Field sampling was conducted in 1402 using a random‑systematic design across six 100‑meter transects and five 2 × 2‑meter plots, where vegetation cover, litter, and bare soil percentages were recorded. Three indicator species—Hammada salicornica, Zygophyllum eurypterum, and Artemisia santolina—were selected for biomass assessment. Their above‑ and below‑ground organs were harvested, and organic carbon content was measured. Soil samples were collected to a depth of 60 cm and analyzed for carbon‑related properties. The results showed that vegetation cover in the rangelands was below the ecosystem’s potential capacity, with two dominant plant functional types identified. Zygophyllum eurypterum exhibited the highest aboveground biomass (31.3 t ha⁻¹) and total carbon stock (79.28 t ha⁻¹), while Hammada salicornica had the highest aboveground biomass among the species, and Artemisia santolina recorded the lowest values. Soil analyses indicated that bulk density, organic carbon content, and soil carbon stock varied significantly among species. These findings demonstrate that plant species with differing ecological traits contribute unevenly to carbon sequestration and ecosystem functioning. Implementing smart rangeland management strategies—such as selecting effective indicator species, restoring degraded vegetation, and improving soil structure—can substantially enhance carbon storage and support long‑term ecosystem sustainability.
 
Extended Abstract
1-Introduction
Climate change and the rise in greenhouse gas concentrations—particularly carbon dioxide—are among the most pressing environmental challenges of the modern era. These changes have far‑reaching impacts on the sustainability of terrestrial and aquatic ecosystems and have been intensified by human activities such as industrialization, land‑use change, and the reduction of vegetation cover. Carbon sequestration, as a key natural process, plays a vital role in regulating atmospheric carbon levels and improving environmental quality. Through plant photosynthesis and the subsequent transfer of organic compounds into the soil, this process enhances the physical, chemical, and biological properties of soils. Soils serve as the largest reservoir of terrestrial carbon, storing more than 70 percent of the carbon in this sector. Although rangelands sequester less carbon per unit area than forests, their extensive global coverage enables them to make a substantial contribution to the global carbon cycle. The carbon sequestration capacity of these ecosystems is influenced by factors such as species composition, ecological conditions, and management practices. Research indicates that drought‑tolerant native species—particularly in arid and semi‑arid regions—possess a higher capacity for carbon storage. Accordingly, the present study aimed to identify the flora of the Sarsaro rangelands in Khash County and to assess the carbon storage capacity of dominant plant species and their associated soils. The findings are intended to provide a scientific foundation for the sustainable management and conservation of this ecologically important rangeland ecosystem.
 
2-Materials and Methods
This study was conducted in the rangelands of Khash County, located in Sistan and Baluchestan Province, an area characterized by an arid to semi‑arid climate with a mean annual precipitation of 149 mm and an average temperature of 18°C. Floristic surveys were carried out in 2023 using exploratory and systematic random sampling. Six 100‑meter transects and five 2 × 2 m plots placed at 20‑meter intervals were established to record vegetation cover, litter, and bare soil percentages. Three dominant species—Hammada salicornica, Zygophyllum eurypterum, and Artemisia santolina—were selected for biomass assessment. For each species, the above‑ and below‑ground organs of ten individual plants were harvested, weighed, dried, and subsequently analyzed in the laboratory to determine organic carbon content. Soil samples were also collected to a depth of 60 cm and examined for key physical and chemical properties. Data analysis was performed using SPSS version 27, and the results were evaluated to determine the influence of species on vegetation cover, biomass production, and carbon storage capacity.
 
3- Results and Discussion
 Vegetation cover in the Khash rangelands was found to be below its potential capacity, largely due to limited and irregular rainfall, shallow soils, and improper grazing practices. Two dominant vegetation types were identified in the study area: Hammada salicornica–Zygophyllum eurypterum and Zygophyllum eurypterum–Artemisia santolina. The first type exhibited 19% vegetation cover and 112 kg/ha of forage production, indicating a poor ecological condition, whereas the second type showed 25% cover and 210 kg/ha of forage production, reflecting a moderate ecological status. A total of 61 plant species belonging to 23 families were recorded, with Asteraceae, Poaceae, and Chenopodiaceae being the most species‑rich families. Approximately 78.6% of the species were associated with the Irano‑Turanian phytogeographic region. Soil analyses revealed no significant differences among species in terms of pH and electrical conductivity. However, bulk density, soil organic carbon, and soil carbon stock showed highly significant differences (p < 0.01). The lowest bulk density was observed under H. salicornica (1.33 g/cm³), while Z. eurypterum exhibited the highest soil organic carbon content (0.272%) and soil carbon stock (24.02 t/ha). Biomass assessments demonstrated that Z. eurypterum had the greatest total carbon storage capacity, with 3.31 t/ha of belowground biomass and 28.79 t/ha of total carbon. H. salicornica ranked second, with the highest aboveground biomass (2.9 t/ha) and a total carbon stock of 22.52 t/ha. A. santolina had the lowest belowground biomass (1.7 t/ha) and the lowest total carbon storage (17.61 t/ha). These findings indicate that plant species with differing ecological traits and biomass allocation strategies contribute variably to carbon sequestration and play distinct roles in supporting rangeland ecosystem functioning.
 
4- Conclusion
 The findings of this study show that plant species with different biomass allocation strategies and ecological adaptations vary considerably in their capacity for carbon storage. Among the examined species, Zygophyllum eurypterum functioned as the most effective indicator species, contributing substantially to carbon fixation and improvements in soil properties, while Hammada salicornica and Artemisia santolina demonstrated comparatively lower contributions. These results highlight the importance of maintaining species diversity and prioritizing drought‑tolerant native species to enhance ecosystem stability and support habitat restoration—an essential foundation for mitigating the impacts of climate change. Effective rangeland management practices, including the selection of appropriate indicator species, vegetation restoration, controlled livestock grazing, and improvements to soil structure, can significantly strengthen ecosystem functioning and carbon storage potential. However, this study has certain limitations, particularly the absence of data on soil microbial communities, seasonal variability, and interactions between plant species and other environmental factors. Addressing these aspects in future research would provide a more comprehensive understanding of carbon storage dynamics and ecosystem processes. Overall, the results of this study offer valuable guidance for policymakers and natural resource managers seeking to restore and sustainably manage arid and semi‑arid rangelands.