Arbuscular mycorrhizal fungi in desert ecosystems: Adaptive mechanisms to co-occurring drought, temperature, and salinity stress

Abstract

Arid ecosystems, covering over 40 % of Earth's land, face increasing stress from drought, salinity, and extreme temperatures. Arbuscular mycorrhizal fungi (AMF) form keystone symbioses with desert plants, enhancing their resilience to these co-occurring stressors. This review synthesizes mechanistic and field-based evidence from deserts (e.g., Caatinga, Atacama, and Arabian Peninsula), showing AMF mediate drought tolerance through osmotic adjustment and improved water/nutrient uptake via extensive hyphal networks. In saline conditions, AMF enhance ion homeostasis, reducing Na⁺ toxicity. Key mechanisms include activation of antioxidant defense systems (e.g., superoxide dismutase, catalase, and ascorbate peroxidase) and modulation of phytohormones (e.g., abscisic acid) and stress-responsive genes (e.g., aquaporins). Morphological adaptations like improved soil aggregation via glomalin-related soil proteins further aid water retention. However, benefits are context-dependent, varying with fungal and host identity, and can be absent under hyper-arid extremes. Field studies confirm native AMF communities, particularly Glomeraceae, are critically adapted for local stress tolerance and are vital for soil health and combating desertification. Their functionality declines at environmental thresholds, underscoring the need to conserve indigenous symbionts. Future research must prioritize multi-stress interactions, molecular cross-talk in tripartite symbioses (e.g., AMF-endobacteria-plant), and developing climate-resilient AMF inoculants for restoration. Integrating omics with field studies will elucidate microbial consortia dynamics, advancing sustainable agriculture in arid frontiers and advocating for AMF-centric approaches to preserve biodiversity in a warming climate.