A Meta-Analysis of the Response of Leaf Photosynthesis Rate to Tropospheric Ozone

Tropospheric ozone (O₃), as one of the primary atmospheric pollutants, poses a global threat to plants, causing ecological stress that severely hinders the achievement of carbon neutrality goals and significantly endangers food security. Photosynthesis is a critical physiological process and a pathway for carbon to enter terrestrial ecosystems. Previously, studies focused only on one or two vegetation types, a single environmental interaction factor, or over a short period. This study compiled 1263 observations from O₃ fumigation experiments published over the past 52 years (from January 1970 to December 2022) and conducted strict data quality control. Through meta-analysis, a comprehensive analysis was conducted on the response of the plant photosynthesis rate to O₃, revealing the impact of the vegetation type, ozone concentration (O₃), combined effects of O₃ with other environmental factors, and tree age on this response. Our meta-analysis results show that elevated O₃ significantly reduces the plant photosynthesis rate by up to 22.29%. The response of photosynthesis rates to the O₃ variation across vegetation types is as follows. Crops, shrubs, and broadleaf trees are the most sensitive, with photosynthetic rate reductions of 25.82%, 23.28%, and 22.14%, while grass and needle-leaf trees have smaller responses, decreasing by 14.51% and 6.70%, respectively. The tree photosynthesis rates increase and then decrease with rising O₃, while for crops, the rate falls first and then rises. As for the combined effects of O₃ with different environmental factors, drought, frost, elevated CO₂ concentration (CO₂), fertilization, and the simultaneous increase of CO₂ and fertilization can alleviate O₃ stress, while shading and high soil salinity will exacerbate O₃ stress when O₃ ≥ 70 ppb. Furthermore, the photosynthetic rate of tree leaves in response to O₃ intensifies with the increasing age of trees, particularly in the case of needle-leaf trees. Our findings provide an important reference for understanding the influence of O₃ pollution on the plant physiological process and carbon cycle of terrestrial ecosystems in the context of global change.