Dust Pollution and Stress Tolerance in Tropical Plants: Unravelling the Physiological Responses and Adaptive Mechanisms of <i>Psidium Guajava</i> L. in Douala, Cameroon

ABSTRACT Airborne particulate matter (PM) pollution increasingly threatens sub‐Saharan tropical cities, yet physiological thresholds for plant resilience remain unclear. This study quantifies dust deposition effects on Psidium guajava L. across urban (PK14), residential (Entrée Kotto), and suburban (Lendi) sites in Douala, Cameroon, over 12 months. Key biochemical traits—dust load (%), chlorophyll, ascorbic acid (AsA), relative water content (RWC), and leaf extract pH, were measured to assess stress responses and the air pollution tolerance index (APTI). Results reveal a nonlinear, threshold‐based response: low‐to‐moderate dust loads (≤ 2.4%) stimulate chlorophyll biosynthesis ( β = 1.607, p = 0.017) and optimize leaf pH (4.76–5.2), enhancing photosynthesis. AsA increases under moderate dust highlighting antioxidant defense activation. Beyond this threshold, excessive dust impairs water content (RWC; r = −0.74, p = 0.01), degrades chlorophyll, and produces APTI values (6.0–9.7) categorizing P. guajava as a sensitive bioindicator. Seasonal‐spatial trends show the moderating role of rainfall and the exacerbating role of urbanization (dust load 3.9% at PK14 vs. 2.4% at Lendi). This pioneering quantitative threshold for a tropical evergreen integrates physiological, biochemical, and tolerance measures, informing targeted urban greening strategies to mitigate pollution impact in tropical cities.