Increasing Wheat Plant Resilience to Climate Variability: The Role of Arbuscular Mycorrhizal Fungi in Adaptation to Drought Stress

1. Introduction

In recent decades, agricultural systems and ecosystems have become increasingly vulnerable to climate change and global warming. Extreme weather events, shifts in rainfall patterns, and water shortages have intensified pressure on crop productivity. Among abiotic stresses, drought remains one of the most important constraints on crop production, plant morpho-physiological performance, and ecosystem stability [1]. Bread wheat (Triticum aestivum L.), one of the world’s most important cereal crops, is particularly sensitive to water scarcity, which can adversely affect biomass production, nutrient absorption, grain productivity, and overall yield. As a result, sustainable biological approaches that enhance crop resilience under environmental stress have attracted increasing research attention.

Arbuscular mycorrhizal fungi (AMF) are among the most important beneficial soil microorganisms because they form symbiotic associations with the roots of most terrestrial plants. Their extensive hyphal networks can improve water and nutrient uptake and enhance plant tolerance to drought through biochemical, physiological, and molecular pathways, including improved osmotic regulation, protection of chlorophyll pigments, and activation of antioxidant defence systems [2,3]. Previous studies have shown that AMF can promote wheat performance under water-limited conditions by supporting photosynthetic activity, reproductive development, and grain filling [4,5]. Accordingly, the objective of this study was to investigate the effects of AMF on selected physiological and morphological responses of bread wheat under water-deficit conditions, with particular attention to photosynthesis, osmotic regulation, growth, and antioxidant activity.

2. Methods

Wheat plants (cultivar Chamran) were cultivated under controlled conditions, and four experimental treatments were applied: (1) well-watered non-mycorrhizal plants (control), (2) drought-stressed non-mycorrhizal plants, (3) well-watered AMF-inoculated plants, and (4) drought-stressed AMF-inoculated plants. Funneliformis mosseae, a widely studied AMF species known to enhance plant tolerance to abiotic stress, was used for inoculation [8]. Soil moisture in drought treatments was maintained at approximately 35–40% of field capacity, whereas control plants were maintained at approximately 75% of field capacity. Soil moisture was monitored regularly by pot weighing and adjusted through controlled irrigation throughout the treatment period. All treatments were conducted with three independent replicates in a completely randomized design. Data from physiological and biochemical measurements were analyzed using one-way analysis of variance (ANOVA), and mean comparisons were conducted using an appropriate post hoc multiple-comparison test at p < 0.05.

This design made it possible to examine both the independent and combined influences of drought stress and AMF colonization on wheat growth and physiological performance. Morphological measurements included shoot growth, root growth, fresh and dry biomass, spike development, and grain weight. Microscopic examination of root samples from inoculated and non-inoculated plants confirmed fungal colonization and characteristic AMF structures. Physiological and biochemical measurements included chlorophyll a, chlorophyll b, total chlorophyll, proline in leaf and root tissues, carbohydrate content, protein content, malondialdehyde (MDA), and catalase activity in roots and leaves. These variables were selected because they are widely recognized indicators of drought-induced stress and adaptive physiological responses in plants [3,9].

3. Results and Discussion

The physiological and biochemical profiles of wheat plants under the control, drought, drought + mycorrhiza, and mycorrhiza treatments are presented in Table 1. Overall, drought stress reduced chlorophyll content and increased stress-associated metabolites such as proline, whereas AMF inoculation improved chlorophyll retention, moderated several stress responses, and enhanced antioxidant activity. Catalase activity was also elevated in AMF-associated treatments, suggesting a stronger antioxidant defence response. These findings are consistent with previous reports indicating that AMF can promote drought tolerance through metabolic, regulatory, and physiological adjustments [10,11].

Table 1 shows that chlorophyll a and chlorophyll b were significantly reduced under drought conditions relative to the control, reflecting impairment of the photosynthetic system. However, AMF inoculation improved chlorophyll retention under both drought and non-drought conditions, with the highest chlorophyll values observed in the mycorrhiza treatment. This finding suggests that AMF helps preserve the photosynthetic apparatus and reduce drought-induced physiological damage, consistent with earlier studies reporting improved chlorophyll stability and photosynthetic performance under AMF symbiosis [12,13].

Proline accumulation increased markedly in leaves and roots under drought stress, confirming the activation of osmotic adjustment mechanisms. In contrast, AMF-colonized plants exposed to drought showed lower proline levels than drought-stressed non-mycorrhizal plants, suggesting partial alleviation of stress. Carbohydrate contents in leaves and roots were also generally higher in AMF-associated treatments, particularly under drought, indicating a possible role in osmotic regulation and carbon metabolism. Together, these results support the view that AMF contributes to improved metabolic balance and stress adaptation in wheat under water-deficit conditions [13,14].

Catalase activity also increased under drought stress and was particularly enhanced in AMF-associated treatments. Leaf catalase activity was highest in the drought + mycorrhiza treatment, while root catalase activity was also elevated under drought. These responses are consistent with activation of antioxidant defence mechanisms that help control reactive oxygen species during water stress. In contrast, MDA values remained relatively stable across treatments, suggesting that lipid peroxidation and membrane damage were limited under the experimental conditions. Similar AMF-associated antioxidant responses have been reported in plants exposed to drought and other abiotic stresses [5,15].

In addition, a correlation heatmap was used to analyze relationships among the measured physiological and biochemical variables (Figure 1). Carbohydrate content, protein levels, and catalase activity showed positive associations, suggesting coordinated metabolic and antioxidant responses under drought stress. By contrast, chlorophyll a, chlorophyll b, and total chlorophyll were negatively associated with stress-related variables such as proline, indicating that increased stress intensity corresponded with reduced photosynthetic performance. Proline was positively associated with several stress-response variables, highlighting its role in osmotic adjustment under drought. Associations involving MDA were comparatively weak, suggesting that oxidative damage was effectively controlled, especially in AMF-treated plants. Overall, the correlation pattern supports the beneficial role of AMF in improving drought tolerance through integrated physiological and biochemical mechanisms.

4. Conclusion

This study demonstrates that arbuscular mycorrhizal fungi can contribute meaningfully to improved wheat resilience under drought conditions. AMF inoculation was associated with improved plant growth, better chlorophyll retention, moderated osmotic stress responses, and enhanced antioxidant activity in water-limited plants. Root microscopy confirmed successful fungal colonization and supported the functional basis of these responses. Overall, AMF represents a promising biological strategy for strengthening sustainable agricultural adaptation to climate variability and drought stress in wheat production.