Melissa dos Santos Cabral¹

Urban expansion affects biodiversity and environmental quality, especially in the Atlantic Forest, one of the most threatened biomes in Brazil. The urban forest remnants deal with two key stressors enhanced by climatic shifts, increased levels of air pollutants, and drought, which compromise and directly affect plant community diversity. Cuticular waxes are widely regarded for their apolar feature, passively protecting against cell water loss and acting as physical/chemical plant defenses from the environment. This study investigated the composition of foliar cuticular waxes as potential biomarkers of environmental changes in four tree species from two Atlantic Forest remnants in the metropolitan area of São Paulo, Brazil: Machaerium nyctitans (Vell.) Benth. (Fabaceae), Alchornea sidifolia Müll. Arg (Euphorbiaceae), Guarea macrophylla Vahl. (Meliaceae), and Casearia sylvestris SW. (Salicaceae). Samples were collected from two distinct urban forest fragments: the Institute of Biosciences Forest Reserve (Matão-IAG, more urbanized) and the Morro Grande Forest Reserve (RFMG, less urbanized). Leaves of six trees of each species and from each area were collected during the dry (Aug–Sep 2023) and the rainy (Jan–Mar 2024) seasons. Cuticular waxes were extracted by leaf immersion three times for 10 s in dichloromethane. The dry extract was derivatized using BSTFA and analyzed by GC-MS. Spectral data were processed using GNPS, followed by multivariate (PCA) analysis using MetaboAnalyst. As expected, results indicate that the wax chemical composition is species-dependent, but seasonality is an important factor in determining the wax composition abundances. We also observed a tendency toward differentiation of the two urban remnants (Matão-IAG vs. RMG), although less clearly defined, which suggests an influence of the urban pollution. Among species, Guarea macrophylla and Alchornea sidifolia showed lower metabolic variability, whereas Casearia sylvestris and Machaerium nyctitans displayed greater plasticity, indicating differentiated responses to environmental stress. Despite still lacking data from Scanning Electron Microscopy (SEM), current results reinforce the role of waxes as biomarkers of environmental quality in urban areas. This study contributes to understanding biosphere-atmosphere interactions in urban environments and expands knowledge on plant physiological responses to environmental stresses. This study was financed, in part, by the São Paulo Research Foundation (FAPESP), Brazil. Process Number 2020/07141-2, and by the National Council for Scientific and Technological Development (CNPq).

Agradecimentos: I thank all my phytochemistry colleagues who have helped me these months, as well as my family and friends for their support and affection.