Antioxidant strategies of four native tree species across seasons in urban and peri-urban Atlantic Forest remnants

Urban Atlantic Forest remnants are exposed to atmospheric oxidants, particularly tropospheric ozone (O₃), and seasonal environmental variability, yet the biochemical basis of tree resilience to these combined pressures remains poorly resolved. We investigated antioxidant strategies in Alchornea sidifolia (AS), Casearia sylvestris (CS), Guarea macrophylla (GM), and Machaerium nyctitans (MN), comparing an urban and a peri-urban site across dry and rainy seasons in São Paulo, Brazil. We quantified ascorbate (AsA) and glutathione (GSH) redox pools, antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT; and ascorbate peroxidase, APX), total phenolic content (TPC), and malondialdehyde (MDA), and integrated these biochemical data with leaf anatomical analyses and cell death assays. Biochemical profiles were structured by species and, to a lesser extent, by season (PERMANOVA: species R 2 = 0.292, p = 0.001; season R 2 = 0.037, p = 0.010; site R 2 = 0.003, p = 0.956). Compact-mesophyll species (AS and CS) showed greater redox stability, but with distinct outcomes. AS combined high constitutive SOD, large AsA pools, and the highest TPC, yet displayed epidermal/mesophyll damage and increased cell death under higher oxidative pressure. CS maintained stable AsA-GSH partitioning, high APX capacity, and minimal anatomical damage across conditions. GM and MN, porous-mesophyll species, did not show coordinated antioxidant compensation and showed greater anatomical damage and cell death. Across species, damage increased in the rainy season, when water availability, temperature, irradiance, and O₃ exposure were higher. Site-related differences were expressed mainly as tissue-level damage and antioxidant pool depletion rather than as coordinated enzymatic induction. Thus, resilience to urban O₃-related oxidative stress and seasonal environmental variability was associated with the integration of structural traits and constitutive redox buffering rather than with coordinated inducible antioxidant responses. These patterns support the use of combined redox and tissue-integrity markers to identify complementary native species for biomonitoring oxidative-stress responses in Atlantic Forest remnants.