Water and Soil

Abstract Introduction
Mycorrhizal symbiosis, particularly arbuscular mycorrhiza, is recognized as one of the most widespread and beneficial interactions between plants and soil microorganisms and has been extensively studied. This symbiosis plays a significant role in improving plant nutritional status, enhancing resistance to both biotic and abiotic stresses, reducing the impact of certain pathogens, and promoting synergistic interactions with other beneficial microbial communities. Ultimately, these effects contribute to improved crop health and productivity. One of the most important benefits of this association is the enhancement of plant nutrition. Mycorrhizal plants acquire nutrients either directly through their roots or indirectly via the hyphal network of symbiotic fungi. The predominance of either pathway depends on a complex set of biochemical and molecular mechanisms within the common symbiosis pathway, as well as phosphorus availability, plant phenotypic traits (especially root characteristics), and environmental conditions. Despite its importance, the degree of mycorrhizal dependency varies among plant species and cultivars. Mycorrhizal dependency is defined as the extent to which a plant relies on mycorrhizal fungi to achieve optimal growth or yield. It is determined by the interaction between plant genotype and phenotype in combination with environmental factors.
Mycorrhizal symbiosis is the result of a complex molecular dialogue between plant and fungus, involving the exchange of signals at cellular, molecular, and genetic levels. In the early stages of symbiosis, plants secrete compounds such as strigolactones from their roots, which stimulate spore germination and hyphal branching. This is followed by fungal signalling molecules, including chito-lipo-oligosaccharides, which act as key signals in the initiation and regulation of arbuscular mycorrhizal symbiosis. Disruption in this shared signalling pathway can lead to failure of symbiosis establishment or reduced mycorrhizal dependency.
Under high nutrient conditions, particularly high phosphorus availability, plant secretion of strigolactones is typically reduced. This illustrates how excess soil phosphorus can interfere with the common symbiosis signalling pathway and thereby decrease mycorrhizal dependency. The synthesis and secretion of strigolactones are regulated by the upregulation of genes such as D27, CCD7, CCD8, and MAX1.
Recent advances in plant molecular biology and genetics have identified a set of genes involved in the common symbiosis pathway that play essential roles in fungal signal recognition, activation of cellular responses, and the formation of fungal structures such as arbuscules. These genes, including SYMRK, CCaMK, and CYCLOPS, will be discussed in detail later. Depending on the upregulation or downregulation of these genes in the plant–fungus symbiotic pathway, a higher or lower degree of mycorrhizal dependency can be expected, respectively.

Materials and Methods
This analytical review integrates findings from researchers in this field by utilizing up-to-date studies on the intensity of plant–fungus symbiosis and the degree of mycorrhizal dependency from morphological, physiological, biochemical, and especially molecular dimensions. These studies are accessible through major international databases, including Web of Science and Scopus. In addition, Google Scholar provides an open-access platform for identifying recent publications, while specialized resources such as ScienceDirect, SpringerLink, and Taylor & Francis offer valuable journal articles, book chapters, and authoritative reference works related to mycorrhizal dependency and the underlying mechanisms involved, particularly from a molecular perspective.

Results
The results of numerous studies indicate that the establishment of symbiosis between plants and arbuscular mycorrhizal fungi requires a series of complex physiological, biochemical, and molecular interactions. This process is initiated by the secretion of Myc-LCO signalling molecules by the fungus, which are subsequently recognized by specific receptors in plant roots, including SYMRK (DMI2). Following recognition, the common symbiosis signalling pathway is activated, and the release of calcium ions (Ca²⁺) through DMI1 generates rhythmic calcium oscillations within plant cells. These oscillations function as informational codes that are decoded by the calcium and calmodulin-dependent protein kinase (CCaMK). The calcium signals are then translated into molecular responses, leading to the activation of the transcription factor CYCLOPS and the regulation of symbiosis-related gene expression, ultimately resulting in arbuscule formation. Any disruption or interruption in this signalling pathway may prevent arbuscule development, particularly in non-host plants. The degree of plant dependence on mycorrhizal fungi is influenced by a range of factors, including plant, fungal, and environmental characteristics. Among environmental factors, abiotic stresses such as drought play a critical role. Under drought conditions, the influx of Ca²⁺ into the plant cell cytosol decreases, leading to disturbances in cellular ion homeostasis. However, the presence of mycorrhizal fungi enhances the expression of calcium-sensing and signalling genes, including CBLs, CDPKs, and MAPKs, thereby activating Ca²⁺-dependent signalling pathways. This process regulates and reinforces the increase in cytosolic Ca²⁺ concentration, which acts as an important secondary messenger during the establishment and maintenance of mycorrhizal symbiosis. Furthermore, numerous studies have demonstrated a significant relationship between mycorrhizal dependency and root morphological characteristics. In general, plant species possessing a magnolioid root architecture exhibit a greater degree of dependence on arbuscular mycorrhizal fungi than species with non-magnolioid root systems.

Conclusions
Although many plant species can establish symbiosis with mycorrhizal fungi, the degree of dependency and effectiveness of this association varies considerably. These differences are largely determined by the complexity of signalling pathways and the regulation of symbiosis-related genes. A deeper understanding of the underlying molecular and cellular mechanisms is essential for improving mycorrhizal symbiosis, although significant challenges remain in its practical application.

Abstract Introduction
Rapeseed (Brassica napus L.), particularly the low erucic acid and glucosinolate cultivars known as canola, is the third largest oilseed crop in the world after soybean and oil palm. In Iran, canola cultivation covers approximately 173 thousand hectares, making it the largest cultivated area among oilseed crops. Golestan and Khuzestan provinces have the largest cultivated areas. Balanced fertilization is crucial for optimizing canola yield, especially under adverse environmental conditions. Plant tissue analysis serves as a fundamental tool for diagnosing nutrient status and exploits the principle that tissue nutrient concentration reflects soil nutrient availability. Advanced diagnostic methods, such as Deviation from Optimum Percentage (DOP) and Nutrient Nalance Index (NBI), provide quantitative measures of nutrient adequacy and imbalance. The DOP method ranks nutrient deficiencies by comparing observed tissue concentrations with those in high-yielding populations. Meanwhile, the NBI integrates multiple nutrient statuses into a single measure (Σ|DOP|) and provides a comprehensive assessment of overall nutrient health.

Materials and Methods
The study was conducted in four provinces: Alborz, Markazi, Golestan, and Ardabil (Moghan region), to reflect the diverse agro-ecological conditions of the country. Thirty farms were randomly selected in each province.
Alborz province (Karaj region) is located at coordinates 35°48'N and 51°10'E. Markazi province (Arak city) is located at coordinates 34°5'30'N and 49°41'30'E. East Golestan Province (Gonbad Kavus region) is located at coordinates 37°16'N and 55°12'E, while Ardabil Province (Parsabad and Moghan regions) is located at coordinates between 39°12'N and 39°42'N and 47°10'E and 48°21'E.
Soil samples were collected from the fields before planting. Plant tissue samples were taken at the begining of stem elongation stage (two-digit growth code 30), which is a sensitive stage for identifying and eliminating nutrient deficiencies before canola flowering. Plant samples were collected as whole plants from 20 random points per hectare, and 20 plants were sampled from each point. Total nitrogen (N), phosphorus (P), potassium (K), and micronutrients zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), and boron (B) were measured in plant tissue. Grain yield was measured at maturity. To assess nutrient status and identify yield-limiting factors, the key diagnostic index, deviation from optimum percentage (DOP), quantifies the deviation in nutrient concentrations from the optimal values observed in high-yielding populations. The NBI index was also used in this study.

Results and Discussion
In terms of soil properties, there was significant variation in pH, salinity, organic carbon, and nutrient availability across the studied provinces.
In Alborz province, the average organic carbon content was low (0.81%) and the frequency of nutrient deficiencies was high, including nitrogen (N, 73%), phosphorus (P, 47%), potassium (K, 20%), sulfur (S, 87%), magnesium (Mg, 37%), iron (Fe, 83%), copper (Cu, 20%), zinc (Zn, 50%), manganese (Mn, 43%), and boron (B, 60%). In Markazi Province, with an average salinity of 1.47 dS/m, severe deficiencies of nitrogen (90%), phosphorus (75%), and potassium (37%) were observed. In Golestan Province, non-saline soils in this region with an average organic carbon percentage of 1.4% showed deficiencies of nitrogen (27%), phosphorus (94%), potassium (32%), magnesium (100%), iron (32%), copper (22%), manganese (31%), and zinc (81%). In Ardabil Province, high clay content (40%) and salinity (2.4 dS/m) led to deficiencies of phosphorus (50%), potassium (1%), sulfur (99%), magnesium (99%), iron (50%), copper (3%), zinc (87%), and manganese (10%).
DOP standards for nutrient concentrations in canola shoots during stem elongation were determined as follows: nitrogen 3.61%, phosphorus 0.46%, potassium 2.8%, sulfur 0.513%, magnesium 0.44%, calcium 1-2%, iron 226 mg kg^-1, copper 1.8 mg kg^-1, manganese 78.5 mg kg^-1, zinc 45.8 mg kg^-1, and boron 54 mg kg^-1.
The nutrient balance index (NBI), calculated as the sum of absolute DOP values, was inversely correlated with yield, confirming that greater nutrient imbalances resulted in reduced yield. Statistical analyses confirmed that NBI thresholds between 133 and 146 corresponded to significant yield reductions (p<0.01). Based on these thresholds, yield decreased by 12 to 18% for each unit increase in NBI. It is noteworthy that when NBI exceeds a certain threshold (NBI breakpoint; BPC), yield reduction becomes more evident. Below this threshold, yield is less affected by NBI. Alborz province had the highest BPC (146), followed by Ardabil (139), Markazi (138), and Golestan (133) provinces, respectively. Farmers and advisors can use this range as a guide for fertilizer recommendations.

Conclusion
This study shows that the variability of canola yield in agro-ecological regions of Iran is primarily due to the deficiency of region-specific nutrients, especially phosphorus and zinc, combined with soil alkalinity, low organic carbon, and mineralogical characteristics. By implementing region-specific nutrient management strategies, yield gaps can be closed, and sustainability in semi-arid oilseed systems can be promoted. The Nutrient Balance Index integrates vital nutrient ratios (such as phosphorus:zinc, magnesium:potassium) to detect imbalances.

Acknowledgement
Authors are thankful to and appreciate Soil and Water Research Institute (SWRI) for supporting the project. The results of this article are derived from the national project number 01-10-10-023-970098 of the Soil and Water Research Institute.

Abstract Introduction Cadmium (Cd) and lead (Pb) contamination of calcareous soils can restrict wheat production in arid and semi-arid regions. High pH and calcium carbonate reduce metal solubility but cannot fully prevent root uptake or food-chain entry. Both metals impair nutrient acquisition, damage chloroplasts and membranes, reduce photosynthesis, and promote reactive oxygen species (ROS) production, causing oxidative damage and redox imbalance. Thiols mediate plant responses to metal stress. Cysteine (Cys) supplies sulfur for glutathione (GSH) synthesis, while glutathione supports redox buffering, antioxidant reactions, metal detoxification, and phytochelatin production. Evidence for simultaneous foliar application of cysteine and glutathione under Cd–Pb stress in wheat grown in calcareous soil remains limited. This study examined the effects of individual and combined thiol sprays on wheat growth, oxidative damage, glutathione redox status, and Cd and Pb accumulation under Cd–Pb co-contamination. Materials and Methods A pot experiment was conducted in a greenhouse at the Faculty of Agriculture, Ferdowsi University of Mashhad. Calcareous clay loam soil was collected from the 0–30 cm layer of agricultural land near Sabzevar, Iran. Soil pH was 7.89 (1:2.5 soil:water), electrical conductivity 2.53 dS m⁻¹, organic matter 1.03%, and calcium carbonate equivalent 24.55%. Diethylenetriaminepentaacetic acid (DTPA)-extractable Cd and Pb were 0.12 and 1.5 mg kg⁻¹, respectively, representing low background levels before contamination. The experiment used a randomized design with five treatments and three replications (15 pots): control without metals, sprayed with deionized water; heavy metals (HM), with 15 mg Cd kg⁻¹ soil and 300 mg Pb kg⁻¹ soil; HM+Cys, with 0.41 mM L-cysteine foliar spray; HM+GSH, with 2 mM reduced glutathione; and HM+Cys+GSH, receiving 0.41 mM cysteine plus 2 mM glutathione. L-cysteine and reduced glutathione (≥99% purity) were obtained from Sigma–Aldrich. Cadmium and Pb were added as Cd(NO₃)₂ and Pb(NO₃)₂ to 5 kg soil per pot. Nitrate input was identical among contaminated treatments and considered a common HM component. Soils were mixed and incubated for four weeks near field capacity before planting. Wheat seeds (Triticum aestivum L. cv. Falat) were disinfected in 5% sodium hypochlorite for 10 min, rinsed three times with deionized water, and sown in pots 23 cm in diameter and 21.5 cm high. Eight seeds per pot were thinned to five plants after establishment. Foliar treatments were applied at tillering, stem elongation, and booting; controls received equal volumes of deionized water. Plants were harvested about 70 days after sowing. Shoot dry biomass was measured after oven drying at 70 °C for 72 h. Total chlorophyll was determined in 80% acetone extracts at 663 and 645 nm following Lichtenthaler (1987). Malondialdehyde (MDA) and Hydrogen peroxide (H₂O₂) were measured at 532 and 390 nm, respectively. Reduced glutathione and oxidized glutathione (GSSG) were assayed in 2% metaphosphoric acid extracts using glutathione reductase, reduced nicotinamide adenine dinucleotide phosphate (NADPH), 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB), and 2-vinylpyridine; the GSH/GSSG ratio was used to assess redox status. Root and shoot samples were wet-digested with concentrated HNO₃ and H₂O₂, and Cd and Pb concentrations were determined by flame atomic absorption spectrometry (AAS) (Analyst 800, PerkinElmer). Oxidative stress index (OSI), total thiol pool, tolerance index, chlorophyll protection efficiency, and transfer factor were calculated. Data were analyzed by one-way analysis of variance (ANOVA), and means were compared using Duncan’s multiple range test. Results and Discussion Combined Cd and Pb stress substantially reduced wheat growth. Shoot dry biomass declined from 12.50 g pot⁻¹ in the control to 7.10 g pot⁻¹ under HM, a 43% reduction. Total chlorophyll decreased from 2.10 to 1.10 mg g⁻¹ fresh weight (47%). All thiol treatments improved both traits. Shoot biomass reached 8.60, 9.60, and 11.00 g pot⁻¹ in HM+Cys, HM+GSH, and HM+Cys+GSH, respectively, while chlorophyll increased to 1.50, 1.70, and 1.90 mg g⁻¹ fresh weight. Tolerance index and chlorophyll protection efficiency showed similar responses. The combined treatment produced the highest values among metal-stressed plants, although neither trait fully reached control values. Oxidative damage increased sharply under HM. MDA increased from 15.00 to 40.00 nmol g⁻¹ fresh weight, while H₂O₂ increased from 4.30 to 12.20 µmol g⁻¹ fresh weight. Cysteine, glutathione, and their combination reduced both indices. MDA concentrations were 32.00, 27.00, and 22.00 nmol g⁻¹ fresh weight in HM+Cys, HM+GSH, and HM+Cys+GSH, respectively; corresponding H₂O₂ values were 9.20, 7.50, and 6.20 µmol g⁻¹ fresh weight. The OSI increased from 0.05 in the control to 0.37 under HM. Cysteine reduced it to 0.17, whereas glutathione alone and the combined treatment both reduced it to 0.10. Therefore, the combined treatment did not exceed glutathione alone for this index, showing that treatment superiority differed among traits. Cd and Pb strongly affected glutathione redox status. GSH declined from 85.30 to 32.90 nmol mg⁻¹ protein under HM, whereas GSSG increased from 15.20 to 31.00 nmol mg⁻¹ protein. Accordingly, the GSH/GSSG ratio declined from 5.61 to 1.07. Thiol application improved redox status in all treated plants. HM+GSH produced the highest GSH concentration, whereas HM+Cys+GSH produced the highest GSH/GSSG ratio. Under the combined treatment, GSH reached 62.70 nmol mg⁻¹ protein, GSSG decreased to 10.50 nmol mg⁻¹ protein, and the GSH/GSSG ratio reached 6.00. This ratio differed significantly from all stressed treatments but not from the control, indicating near-control redox restoration. Thiols also reduced Cd and Pb accumulation. Under HM, Cd concentrations were 19.0 mg kg⁻¹ in roots and 7.6 mg kg⁻¹ in shoots; under HM+Cys+GSH, they decreased to 10.4 and 4.0 mg kg⁻¹, respectively. Root Pb declined from 25.5 to 12.5 mg kg⁻¹, while shoot Pb declined from 9.8 to 5.5 mg kg⁻¹. Cysteine and glutathione alone also lowered both metals, although differences between HM+GSH and HM+Cys+GSH for shoot Cd and Pb were often not significant.Transfer factors for Cd and Pb remained below 0.5, indicating limited root-to-shoot translocation. Roots retained a substantial proportion of absorbed metals, reducing but not eliminating accumulation in shoots. Conclusion Cd–Pb co-contamination reduced wheat shoot biomass and chlorophyll, increased MDA and H₂O₂, and disrupted glutathione redox balance. Foliar cysteine and glutathione alleviated these effects. Their combined application produced the strongest response for most growth, oxidative, redox, and tissue-metal traits, improving biomass and chlorophyll, reducing oxidative damage, restoring GSH/GSSG to a control-comparable value, and lowering Cd and Pb in roots and shoots. Transfer factors remained below 0.5, indicating limited root-to-shoot translocation. Field validation and grain-metal measurements are required before recommending this treatment for food production. Acknowledgement The authors acknowledge the Faculty of Agriculture, Ferdowsi University of Mashhad, for providing greenhouse and laboratory facilities for this study.

Abstract Introduction A large amount of precipitation is lost annually. Therefore, studying the precipitation-runoff process and predicting runoff are essential in water resources studies and plans, as well as in water engineering discussions. Thus, choosing a model that can predict runoff from rainfall with acceptable accuracy using effective factors seems essential. The aim of this research is to estimate the components of unit hydrographs resulting from several precipitation-runoff events in the Samian Watershed located in Ardabil Province using a nonlinear optimization method along with the application of probability distribution functions. Materials and Methods In order to determine the optimal values of the distribution function parameters, the objective function is considered as minimizing the sum of the squares of the deviation between the predicted and actual direct runoff hydrographs. The values of the probability distribution functions parameters are optimized using Mathematica software and nonlinear programming method. Finally, the direct runoff hydrographs are calculated using the effective rainfall hydrographs and the corresponding unit hydrographs, and then compared with the observed direct runoff hydrographs. The performance criteria of mean square error, mean absolute error ,and correlation coefficient are used to examine the ability of the functions in the calibration and testing stages. The classical least squares method is also used to extract the unit hydrographs and its efficiency is compared with the results of the nonlinear optimization model. Results and Discussion In the calibration period, for the first event, the Root Mean Square Error (RMSE) and Mean Absolute Error (MAE) of the Gumbel (0.0048 and 0.0042) and Nakagami (0.0134 and 0.0095) functions are higher and their Correlation Coefficients (CC) (0.935 and 0.237, respectively) are also lower than those of the other functions. The lowest errors (0.0021 and 0.0016) and the highest correlation coefficient (0.978) are related to the lognormal distribution. The weakest distribution is the Nakagami distribution with RMSE equal to 0.0134, MAE equal to 0.0095, and CC equal to 0.237. In the case of the second event, the RMSE and MAE errors of the Gumbel (0.0110 and 0.0070) and Nakagami (0.0223 and 0.0293) functions are higher and their correlation coefficients (0.682 and -0.087) are also lower than the other functions. The lowest errors (0.0068 and 0.0056) and the highest correlation coefficient (0.874) are related to the lognormal distribution. The weakest distribution is the Nakagami distribution with RMSE of 0.0223, MAE of 0.0293, and CC of -0.087. In the case of the third event, the performance of all functions is satisfactory due to very low RMSE and MAE values and very high correlation coefficient. However, the errors of the gamma and lognormal functions are slightly higher than the others. Also, Weibull and normal distributions show better performance than other distributions based on the values of performance criteria because these distributions show high ability in predicting the ascending and descending branches of the unit hydrograph. In the test period, considering the average values of the performance functions of the distributions in each event, it can be said that the lognormal distributions (with average RMSE and MAE errors of 0.0134 and 0.01115 and average correlation coefficient of 0.823) and the normal distributions (with average RMSE and MAE errors of 0.0142 and 0.01275 and average correlation coefficient of 0.739) have higher potential in estimating the unit hydrographs of the basin, respectively. The errors of Pearson and Nakagami distributions in both events were higher than the other distributions. The least squares method also had better performance criteria values than all distributions in both events. Conclusion In general, according to the results obtained in the calibration and testing periods, it can be concluded that the lognormal distribution is the best distribution for estimating and calculating unit hydrographs (especially in estimating the ascending branch and peak time and discharge) in the Samian Basin. Also, the Pearson and Nakagami functions are among the weakest distributions in estimating the hydrographs of that basin. The least squares method, regardless of its shortcomings, is among the appropriate methods in estimating the unit hydrograph.

Abstract Introduction
Dust is one of the most important environmental hazards in arid and semi-arid regions and can affect vegetation health through reducing incoming radiation, depositing particles on leaf surfaces, disrupting photosynthesis, and intensifying environmental stresses. Khuzestan Province is considered one of the major dust-affected regions in Iran due to its geographical location, proximity to domestic and transboundary dust sources, sensitive wetlands, extensive agricultural lands, recurrent droughts, and land-use changes. The reduction of wetland water levels, decline in soil moisture, improper water resource management, and human activities have also increased the vulnerability of this region. Since vegetation plays an important role in soil stabilization and the reduction of wind erosion, investigating the effects of dust events on vegetation conditions is of great importance for environmental and agricultural management. The aim of this study is to analyze the temporal effects of dust events on vegetation health in Khuzestan Province during the period 2001–2023 using remote sensing and atmospheric reanalysis data.

Materials and Methods
In this study, monthly data for the period 2001–2023 were used. To monitor dust intensity, dust aerosol optical depth at 550 nm obtained from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) dataset was employed. In addition, total AOD and the ratio of dust AOD to total AOD were calculated to examine the contribution of dust to the total aerosol burden over the region. Vegetation health was evaluated using two indices, Normalized Difference Vegetation Index (NDVI) and EVI, derived from the Moderate-resolution Imaging Spectroradiometer (MODIS) MOD13A2 product, version 6.1. NDVI was used as an indicator of vegetation greenness and density, while EVI was applied because of its lower sensitivity to atmospheric effects and vegetation saturation.
The 16-day NDVI and EVI data were converted to a monthly scale and synchronized with the AOD data. Then, monthly anomalies of AOD, NDVI, and Enhanced Vegetation Index (EVI) were calculated to remove the effect of the seasonal cycle. Severe dust events were identified using percentile-based statistical thresholds; the 75th percentile was calculated as 0.296, and the 90th percentile as 0.360. Months with AOD values equal to or greater than the 90th percentile were selected as severe dust events. Subsequently, the relationship between dust and vegetation indices was examined using Pearson correlation, linear regression, seasonal analysis, month-by-month analysis, lag-correlation analysis, and event-based analysis.

Results and Discussion
The results showed that dust AOD in Khuzestan Province experienced considerable temporal fluctuations during the study period. In total, 70 months were above the 75th percentile and 29 months were above the 90th percentile, indicating the occurrence of relatively severe and severe dust events. The relative synchronization between variations in dust AOD and total AOD showed that dust constitutes an important part of the aerosol burden over the region.
The analysis of NDVI and EVI anomalies indicated that vegetation health changed noticeably during the study period, and both indices showed similar behavior in many periods. In the first step, the relationship between raw AOD and vegetation index anomalies was negative but weak; the correlation coefficient between raw AOD and NDVI anomaly was -0.144, while that between raw AOD and EVI anomaly was -0.132. This weak relationship is probably due to strong seasonal cycles and the simultaneous influence of climatic and agricultural factors.
After removing seasonal effects, the strength of the relationship increased. The correlation coefficients between AOD anomaly and NDVI and EVI anomalies were -0.307 and -0.281, respectively, and both relationships were statistically significant. This result indicates that abnormal increases in dust are generally associated with a relative decline in vegetation health. Seasonal analysis also showed that this relationship was stronger in spring; the correlations between AOD anomaly and NDVI and EVI during this season were -0.388 and -0.346, respectively. This may be related to active plant growth and the greater sensitivity of agricultural crops during this period.
Lag analysis showed that the effect of dust was not limited to the month of occurrence and continued for several months afterward. The strongest negative correlation was observed in the same month as the dust event; however, negative relationships remained at one-month, two-month, and three-month lags. In addition, event-based analysis showed that after severe dust events, the mean anomalies of NDVI and EVI decreased further in the following months. This may indicate the cumulative effect of dust, reduced photosynthetic capacity, decreased surface moisture, or the coincidence of dust events with climatic stresses.

Conclusion
The results of this study showed that there is a negative, significant, and complex relationship between dust events and vegetation health in Khuzestan Province. The use of AOD anomalies provided a more accurate representation of the effect of dust on vegetation compared with raw AOD values. The findings indicate that abnormal increases in dust, particularly in spring and in some sensitive months, are associated with relative decreases in NDVI and EVI. However, vegetation health is not affected by dust alone, and factors such as precipitation, temperature, soil moisture, irrigation, crop type, planting time, and agricultural management also play important roles. Therefore, for a more accurate interpretation of this relationship, the integration of remote sensing data with climatic, hydrological, and field data is recommended.

Abstract Introduction
Drought can be considered one of the most significant hazards for sustainable living in rural areas of Iran, many regions of which are characterized by arid and semi-arid climates. During the last decades, drought occurrence has led to a decrease in the provision of ecosystem services and negative socio-economic consequences. Moreover, pressure on surface and underground water has been rising, especially in the agriculture-focused Fars Province. Despite numerous drought assessment studies performed in Iran, the use of composite indexes that would integrate both social and environmental aspects of drought resilience on the basis of objective and available data is relatively rare. Indeed, earlier studies had used narrow criteria sets or questionnaire-based approaches to estimate social resilience, without developing a replicable data-driven approach. However, such a development is needed due to the multi-dimensional nature of the concept, which encompasses several factors like land use dynamics, population trends, agricultural diversity, irrigation systems, education, and employment age structure. Therefore, development of a composite index to analyze all those factors is required for effective decision-making in this field. In this paper, the analysis of social resilience to drought on the basis of the LPCIEA composite index is conducted in two rural settlements – Mohammadabad and Majdabad – of Marvdasht County, Fars Province, over a 24-year period (2000-2024).

Materials and Methods
LPCIEA composite index includes six criteria: Land use (L), Population (P), Crop diversity (C), Irrigation level (I), Education (E), and Employment age (A). Data on these criteria were collected from various sources: Landsat ETM (2000) and Sentinel-2 (2024) imagery for land use classification and Normalized difference vegetation index (NDVI) calculation; census statistics and village level data for population and education; and field survey for irrigation level and crop diversity. Image pre-processing, including atmospheric and geometric correction, was carried out in Environment for Visualizing Images (ENVI) 5.6, while maps of land uses were created on the basis of Support Vector Machines (SVM) classification with accuracy from 86% to 91% and Kappa index from 0.82 to 0.89. Crop diversity was estimated on the basis of Shannon-Wiener index. All variables were standardized using the Min-Max method to 0-1 scale. Weights for each criterion and sub-indicator were objective and estimated by means of Principal Component Analysis (PCA), which accounted for 76.4% of total variance using five principal components. Resilience score (R) for each village was calculated as a linear weighted combination of six standardized criteria. Multiple regression analysis (ENTER method) was used to determine contributions of each criterion to total resilience. Model validation was carried out using Durbin-Watson statistic and tests for multicollinearity (VIF and Tolerance), while spatial maps of resilience were generated for 2000 and 2024.

Results and Discussion
Over the period of 24 years, 12 states of resilience were identified for the two villages and six criteria. Six of them were red ("very low resilience"), three were yellow ("moderate but declining") and only three states were green ("favorable"), which indicates the dominance of critical states and a long-term erosive trend. The regression model had excellent goodness-of-fit, with multiple correlation coefficient (R) of 0.995 and adjusted R² 0.98, while Durbin-Watson statistic of 1.892 indicates the absence of autocorrelation. Out of six criteria, "Crop diversity" (C) had the greatest positive and statistically significant effect on resilience with the beta coefficient of 0.785 (p < 0.01), contributing to 96% of explained variance. On the contrary, "Education" (E) had the lowest effect (β = 0.095, p = 0.63), which indicates that despite the considerable increase in literacy rates, it had little influence on drought resilience in compared with agricultural diversification and irrigation. Other criteria in order of importance were Population (β = 0.465), Employment age (β = 0.430), Land use (β = 0.380), and Irrigation (β = 0.250). The derived regression equation is as follows: R = 1.450 + 0.090L + 0.220P + 0.185C + 0.110I + 0.040E + 0.145A. According to temporal analysis, Majdabad village showed considerable population growth (resilience score from 46 to 77), Mohammadabad village showed moderate growth (44 to 50), while both villages suffered from a severe decrease in crop diversity (from 42 to 7 points) and irrigation level (from 36 to 16 points), which is a consequence of water shortage. On the other hand, the education score increased substantially (from 8 to 41-46 points), but did not lead to the corresponding increase in resilience because of the priority of production-related factors.

Conclusion
It is evident that drought resilience in the analyzed villages is mostly determined by crop diversification and availability of water resources, rather than demographic and educational factors. Majdabad village, which has greater population (8,970 people) and greater pressure on resources, needs urgent adaptive measures, followed by Mohammadabad. The dominance of red-status resilience states (6 of 12) indicates critical a threshold, and immediate policy measures are needed. Therefore, the following recommendations can be made on the basis of this research. It is necessary to focus the supportive policies on increasing crop diversity, promotion of crops with low water demand and diversification of the agricultural portfolio. Equally important is active participation of local communities in decision-making bodies – like strategic planning, priority setting and budget allocation, which will promote social cohesiveness and joint actions. Different villages showed different adaptive capacities under similar climatic conditions, therefore, a differentiated rather than general strategy is needed. The index LPCIEA, which provides objective weighting based on PCA and uses replicable satellite and census data, is a useful instrument for periodic resilience monitoring. Future research should expand this approach to other regions and incorporate climate projection scenarios into it.

Acknowledgement
This work is derived from part of the results of an independent research subproject entitled "Analysis of Social Resilience to Drought Using a Composite Index (Case Study: Fars Province)", with code 0-66-29-012-010495 and approved by the Soil Conservation and Watershed Management Research Institute. The authors of this article would like to acknowledge the cooperation and support of that research institute and the support of the Fars Agricultural and Natural Resources Research and Education Center.