Integrating Remote Sensing and Metabolomics to Assess Synergistic Effects of Phosphate Deficiency, Drought, and AMF...

Soybean growth and yield are susceptible to abiotic stresses such as phosphate (P) deficiency and drought. Symbiotic association of plant roots with arbuscular mycorrhizal fungi (AMF) can improve water uptake, thereby increasing stress resilience. This study evaluates the interactive effects of P availability, drought, and AMF symbiosis on physiology, reflectance traits, roots, and metabolite responses in two soybean genotypes during the early reproductive stages. Under P deficiency (P-), AMF colonization significantly (p < 0.05) increased, enhancing root hair development and maintaining ~30% lower leaf water potential (Ψ) under drought stress. Drought significantly (p < 0.05) negatively impacted photosynthesis as well as triggered shifts in metabolite accumulation and reflectance-based vegetation indices in both P treatments. P- sufficient (P+) plants developed significantly higher biomass. Chlorophyll-related vegetation indices were more responsive to P during drought, showing 45%-60% reductions in P- plants compared with only 25%-35% in P+ plants. The ratio of red-to-far-red chlorophyll fluorescence also significantly decreased (10%) under drought, indicating altered canopy spectral balance and stress-induced pigment changes. Carbohydrates, jasmonic acid, and amino acids exhibited significant variations (p < 0.05) among genotypes and P treatment under drought. Interestingly, a metabolite involved in phylloquinone biosynthesis (C₁₁H₁₂O₆) was strongly upregulated under drought in P- plants with a strong correlation (r = 0.72) to Ψ. These findings highlight the critical role of P in AMF symbiosis for drought resistance. The integration of remote sensing and mass spectrometry-based metabolite profiling provides a comprehensive multiscale approach to link physiological and molecular responses, facilitating rapid and informed breeding decisions under diverse environmental stresses.