The purpose of this study was to investigate the causes of wilt of hand-planted Haloxylon in terms of vegetation and soil characteristics in Ardestan plain in an area of 583.94 hectare. Samples were taken from three one-hectare, juicy, semi-withered and withered areas in three replications. In order to determine the effect of each factor on the wilt of Haloxylon, the data were analyzed by factorial method based on completely randomized block design. The results showed that there were significant differences in abundance, age of soil, soil pH, SAR and Ec limitations, soluble magnesium deficiency at 99% and soluble sodium at 95% probability level. It seems that due to physiological conditions and adaptability of the species, soil factors are tolerable for this species. Therefore, it is recommended that the native populations of the area be harvested on a regular basis from the elderly populations on condition of expert supervision to control the density and age of the paddy fields as well as to prevent pests.

Tree species can cause changes in soil characteristics and organic carbon storage due to their tolerance to harsh environmental conditions. Therefore, by knowing the species that have more ability to store carbon, it would be possible to follow the improvement and regeneration of urban forests from the perspective of carbon sequestration index. Haloxylon ammodendron and Tamarix hispida shrubs are among the important halophyte species of the Irano-Turanian vegetation zone. In these areas, it is important the role of these shrubs in storing carbon and increasing plant biodiversity. The current research aims to investigate the soil carbon sequestration and plant biodiversity indicators in the habitats of these two species in Qom province.

The natural habitat of Tamarix located in Mesila plain of Qom province and the cultivated habitat of Haloxylon in 1362, located in Hossein-Abad area of Mish-mast in Qom plain with arid climate. Soil sampling was done randomly on one hectare with 30 samples from the eastern direction under the canopy and outside the canopy, by a cylinder at the depth of 0-15 cm in both Haloxylon and Tamarix habitats separately. Sampling was done to calculate the soil organic carbon reserve to obtain the apparent specific mass and organic carbon and some soil physical and chemical factors. To study the vegetation coverage in each habitat, from a plot of 400 m2 with the method of implementing the plot in the form of four plots of 10 x 10 meters in order to better distribute it on the surface of one hectare, and to study the vegetation of the floor from 20 micro-plots of one m2 (five micro-plots in each plot) was used. The values of species diversity in each microplate from each sample plot was calculated using Simpson, Shannon-Wiener indices and species richness using Margalef, Menchick and uniform indices with Pillo and Sheldon indices. Spearman's test was used to calculate the correlation between soil carbon deposition factors and some physical and chemical factors.

The average of all measured factors in the soil was higher for Tamarix. The effect of species and sampling position and the mutual effect of species in sampling position on the amount of acidity factors, percentage of organic carbon, potassium and carbon deposition (organic carbon storage) of the soil had a significant difference at the level of 5%. Furthermore, based on the comparison of the average of the treatments, it was found that the highest amount of soil carbon deposition is in the treatment under canopy of the Tamarix shrub with the amount of 191.13 tons per hectare. The results showed a significant difference in the amount of soil carbon sequestration between two species of Haloxylon and Tamarix, and it is higher in Tamarix soil. Soil characteristics such as carbon deposition, %OC, pH and K under canopy of Tamarix are higher than outside the canopy. The correlation between carbon sequestration characteristics and other factors showed that OC, pH and EC factors can be used as the most important influencing factors to estimate soil carbon sequestration. The indicators of plant biodiversity, including species diversity, species richness and uniformity, were calculated for each micro-plot only in Haloxylon habitat, because the Tamarix habitat was lack of floor cover and reproduction due to severe drought stress. The Menhinik and Margalef indices with the values of 1.39 and 1.68, respectively, have assigned the average species richness of Haloxylon habitat.

Due to the positive effect of Tamarix on the increase of organic matter and soil carbon deposition, which improves the soil structure in the long term, as well as the ability to adapt and resist the dry and fragile weather conditions of Mesileh region. The revival of this valuable species is vital and it is a suitable species for forestry in areas with such characteristics. Likewise, considering the positive effect of Haloxylon species in increasing habitat biodiversity indicators, which in the long term protect the soil structure, the issue of preserving and revitalizing these valuable plants is necessary for Qom province.