【Objective】Rapid industrialization and urbanization under climate change have intensified atmospheric pollution across many regions of China. Ozone(O₃), a phytotoxic secondary pollutant with increasing concentrations, has become a major summer time air pollutant in urban areas, posing serious threats to ecological security. Leaves of different ages may exhibit varying sensitivity or responses to atmospheric ozone (O₃) pollution, and the physiological mechanisms underlying age-related differences in photosynthetic responses remain to be fully elucidated. This is crucial for a comprehensive understanding of the response mechanisms of bamboo species to atmospheric O₃ pollution. This study investigated the effects of elevated O₃ concentration(eO₃) on the urban landscaping bamboo species Indocalamus decorus to assess whether leaf age influences the O₃ resistance of I. decorus, and to elucidate the mechanistic links between chlorophyll fluorescence parameters and photosynthetic impairment.【Method】Nine open-top chambers (OTCs) were established with three O₃ treatments in a suburban area of Changping District, Beijing. The OTCs, constructed with aluminum alloy frames and covered with 10 mm thick transparent plastic film (90% light transmittance), were 2.5 m in height and 2 m in diameter, with a ground area of 3.14 m² and spaced 2 m apart. I. decorus, a small evergreen ornamental bamboo with significant economic value in China and broad applications as a sustainable “bamboo-as-plastic” substitute, was selected as the study species. It is commonly used in food packaging, temporary shelters, boat canopies, hat weaving, and textile manufacturing. Rhizomes of uniform age (five years), color, and thickness were selected, and 10 cm segments with consistent length and bud number were propagated. After one year, uniform seedlings were transplanted for the experiment. During the growing season, chlorophyll content, gas exchange, and chlorophyll fluorescence parameters were measured in both mature and newly emerged leaves. In view of rising O₃ levels in Beijing and the known O₃ tolerance of I. decorus, the O₃ treatments included ambient air (AA), AA + 70 ×10^-9 O₃ (AA+70), and AA + 140 ×10^-9 O₃ (AA+140). O₃ fumigation was conducted daily from 8:30 to 17:30 (9 h), starting on June 1st and ending on October 12th.【Result】(1) SPAD values of old and new leaves exhibited contrasting responses to O₃. Under AA+70 and AA+140 treatments, SPAD values of old leaves decreased by 10.5% and 7.8%, respectively (P<0.05), whereas SPAD values of new leaves increased by 6.3% under AA+140. A significant interaction between eO₃ and leaf age was observed, with eO₃ amplifying SPAD differences between leaf ages. (2) eO₃ significantly reduced the maximum photosynthetic rate (A_sat) and stomatal conductance (Gs) of older leaves under saturating light, but had no significant effects on younger leaves. The photosynthetic decline in older leaves was primarily attributed to non-stomatal limitations.(3) eO₃ significantly decreased the actual quantum yield of PSⅡ (ΦPSⅡ), quantum efficiency of CO₂ assimilation (PhiCO₂), and electron transport rate (ETR) in both young and old leaves, with more pronounced reductions in older leaves. Additionally, eO₃ reduced both photochemical quenching (qP) in young leaves. A significant interaction between eO₃ and leaf age on PhiCO₂ was observed, indicating that eO₃ exacerbated the differences between young and old leaves.【Conclusion】Elevated O₃ concentration induces chlorophyll degradation and PSⅡ photodamage in mature leaves, suppressing light reactions (reduced ΦPSⅡ) and electron transport (lowered ETR), thereby impairing photosynthesis. In contrast, new leaves exhibit compensatory mechanisms: preferential allocation of resources (e.g., photoassimilates and antioxidants) helps stabilize chlorophyll content and maintain A_sat, sustaining overall photosynthetic performance. This leaf-age-dependent resource allocation strategy—prioritizing younger leaves—enhances population-level O₃ tolerance in I. decorus, underscoring its ecological adaptability and reinforcing its potential as a sustainable “bamboo-based plastic alternative”. Future studies should investigate the long-term effects of O₃ on chlorophyll fluorescence dynamics to better understand photosynthetic acclimation. This study provides precise data and theoretical support for understanding the impacts of air pollution on bamboo growth, offers a scientific foundation for the development of eco-friendly and sustainable bamboo industries, and contributes predictive insights into the effects of future climate change on urban green vegetation.