Changes in Soil Microbiome Composition and Tomato Plant’s Physiological Response to Water Deficit and Excess

Water stress is a major limiting factor in agriculture, particularly in the Mediterranean region, where climate change exacerbates drought conditions. Soil microbiome composition plays a crucial role in plant resilience to environmental stressors, particularly water scarcity and excess. This study examines the impact of different irrigation regimes (optimal, severe deficit, and excess) on tomato soil microbiome composition and plant physiology in a Mediterranean context. Metataxonomic profiling revealed significant shifts in microbial community structure: Proteobacteria dominated under optimal irrigation (WO), Acidobacteria under water deficit (WD), and Actinobacteria under both water deficit and excess (WE). Functional analysis indicated irrigation-induced alterations in microbial metabolic pathways, influencing nutrient cycling. Soil respiration varied, peaking in the WE condition. Plant physiological responses, including gas exchange and Proline content, were significantly affected by water stress. An inverse correlation was observed between microbial diversity and chlorophyll content, suggesting a link between plant stress responses and soil microbial composition. This study underscores for the first time the intricate relationship between water availability and microbial community dynamics, emphasizing the importance of microbiome-driven soil and plant resilience, thus showing this be a key factor in agricultural sustainability under changing climatic conditions.