Global meta-analysis unravels mechanistic shifts in plant growth and physiological adaptability under nitrogen...

Quantitatively elucidating plant responses to elevated nitrogen dioxide (eNO₂) is essential for understanding global atmospheric nitrogen pollution and ecosystem nitrogen cycling, yet a comprehensive synthesis is still lacking. Here, we integrated data from 80 independent experiments worldwide and conducted a multivariate mixed-effects meta-analysis to evaluate the effects of eNO₂ on 73 plant traits encompassing growth, physiology, and biochemistry. Overall, eNO₂ significantly reduced plant growth performance and diminished environmental adaptability by disrupting water regulation, photosynthesis, mineral nutrient uptake, and hormone-mediated processes. Subgroup analyses based on the between-group heterogeneity (Q_B) statistic revealed that plant functional types were major determinants of response variability; specifically, clonal, herbaceous, deciduous, and C₃ species exhibited greater sensitivity to eNO₂. Linear and nonlinear dose-response analyses, including restricted cubic spline (RCS) models, further demonstrated that plant responses were jointly shaped by exposure concentration and duration, and that chronic low-level eNO₂ could induce growth stimulation resembling hormone-like regulatory effects. Collectively, this study provides the comprehensive quantitative framework for understanding plant responses to eNO₂, offering critical insights into the mechanisms underlying plant adaptation to atmospheric nitrogen pollution and informing the design of nitrogen-cycle manipulation experiments.