بررسی تاثیر روش‌های مختلف ذخیره نزولات و تیمارهای اصلاحی خاک بر استقرار و شاخص های رشد گیاه دیوخار (Lycium depressum (L.)) و سیاه تاغ (Haloxylon ammodendron (C.A. Mey.))

Background and Objectives: One of the limitations of vegetation in arid and semi-arid regions is their limited access to water. In these environments, precipitation is not only scarce but also highly unpredictable, often occurring in brief, high-intensity events. Such rainfall patterns frequently exceed the infiltration capacity of soils, resulting in substantial surface runoff. Consequently, a large proportion of available water is lost before it can be utilised by plants, exacerbating land degradation and contributing to desertification. To mitigate these adverse effects, effective rainwater harvesting techniques are essential for improving soil moisture retention and supporting sustainable plant establishment. Mechanical interventions—such as in-situ water conservation structures—can enhance initial water availability and promote seedling survival. However, their long-term effectiveness may decline due to environmental stress, structural degradation, or inadequate maintenance, necessitating periodic rehabilitation. Furthermore, achieving resilient and self-sustaining vegetation in fragile dryland ecosystems requires the integration of biological strategies with mechanical approaches. *Limonium depressum* and *Haloxylon ammodendron* are two drought-tolerant plant species well-adapted to extreme abiotic conditions, including high temperatures, salinity, and poor soil fertility. Their ecological resilience makes them suitable candidates for rangeland rehabilitation and reclamation of degraded lands in arid zones. This study was conducted to evaluate the effects of different rainwater harvesting systems and soil amendment treatments on the establishment and early growth performance of *L. depressum* and *H. ammodendron* in the desert areas of southern North Khorasan Province, Iran, specifically within Jajarm County.
Materials and Methods: The study was carried out in a flat, sparsely vegetated desert region located approximately six kilometres downstream from the Alumina Factory mines in Northern Jajarm County. The area is characterised by fragile soils with low organic matter, poor water-holding capacity, and high susceptibility to wind and water erosion. A factorial experiment was designed based on a randomised complete block design (RCBD) with 13 replications to ensure statistical reliability and minimise environmental variability. The two plant species, *L. depressum* and *H. ammodendron*, were planted at 5-meter intervals to reduce interspecific competition and allow adequate space for growth. Three rainwater harvesting techniques were evaluated: Crescent-shaped catchments, Pitting, and Contour Furrows. These methods were selected based on their proven ability to capture and retain runoff water, thereby enhancing soil moisture. Each harvesting system was combined with five soil amendment treatments: (1) clay-acrylic resin nanoparticles applied at 1% and 3% concentrations to improve soil aggregation and water retention; (2) a mixture of mycorrhizal fungi (*Glomus intraradices*, *G. mosseae*, and *G. fasciculatum*) to enhance root nutrient and water uptake; (3) straw mulch to reduce evaporation and moderate soil temperature; (4) zeolite applied at 300 g and 600 g per planting site to improve cation exchange capacity and water retention; and (5) an untreated control for baseline comparison. Key growth and establishment parameters—including survival rate (establishment), canopy cover, plant height, large diameter, and small diameter—were measured during the first year after planting. Data were analysed using analysis of variance (ANOVA), and mean comparisons were performed using Tukey’s test at a 5% significance level. Statistical analyses were conducted using Minitab software (version 16), with separate evaluations for each species to account for species-specific responses.
Results: The Contour Furrow method for *Limonium depressum* demonstrated superior performance in promoting plant establishment -the highest survival rate (99.14%)-, significantly outperforming Pitting and Crescent-Shaped catchments. Similarly, *Haloxylon ammodendron* achieved its highest establishment (88.59%) with Contour Furrows, while Pitting resulted in the lowest establishment (79.46%). Soil amendment treatments had a significant effect only on the small diameter of *L. depressum*, with no statistically significant impact observed on *H. ammodendron*. Rainwater harvesting systems significantly influenced multiple vegetative traits in *L. depressum*, including canopy cover, plant height, and both large and small diameters. In *H. ammodendron*, only canopy cover and large diameter were significantly affected. Further analysis revealed that in *L. depressum*, the 1% nano-clay treatment yielded the greatest plant height, whereas the second type of mycorrhizal fungus resulted in the lowest. The largest plant diameter was recorded under the 3% nano-clay treatment, while the smallest was observed in the straw mulch treatment. The control group showed the highest small diameter, suggesting potential inhibitory effects of certain amendments. For *H. ammodendron*, the 300 g zeolite treatment produced the best results across all growth parameters, whereas the 1% nano-clay treatment consistently yielded the lowest values. Canopy cover and large diameter were maximised under Pitting, while height and small diameter were greatest under Contour Furrows. Overall, enhanced growth was associated with effective water harvesting and beneficial amendments such as zeolite and nano-clay, while reduced performance was linked to less effective treatments like 1% nano-clay and certain mycorrhizal applications.
Conclusion: The study demonstrates that the response to soil amendment treatments varies significantly between the studied plant species. While *L. depressum* showed a measurable response in small diameter to soil amendments, *H. ammodendron* exhibited no significant response, likely due to its inherent resilience to harsh soil conditions. This differential response underscores the importance of matching species traits with appropriate restoration techniques. L. depressum demonstrates a higher adaptability to improved soil conditions, resulting in a more favourable response to amendment treatments compared to H. ammodendron, which is a resilient species adapted to harsh environments. Contour Furrows proved to be the most effective rainwater harvesting method for both species, attributed to their ability to distribute runoff and enhance water infiltration uniformly. These findings support the integration of Contour Furrow systems in dryland rehabilitation projects. Although short-term impacts of soil amendments were limited, their long-term benefits—such as gradual improvements in soil structure, nutrient retention, and microbial activity—may become more pronounced over time. Therefore, long-term monitoring is essential to fully assess the cumulative effects of soil amendments on plant growth and ecosystem recovery in arid and semi-arid environments. The observed species-specific responses highlight the need for tailored restoration strategies that consider both ecological adaptability and site-specific conditions to maximise reclamation success.