Differential associations of dry and wet nitrogen deposition with vegetative and reproductive plant traits across China

Atmospheric nitrogen (N) deposition is a major component of global environmental change and is spatially structured across climatic and edaphic gradients. However, at macroecological scales, how dry and wet N deposition covary spatially with different plant functional traits, and whether these associations differ across environmental contexts, remain insufficiently quantified. Across China, both dry and wet nitrogen deposition were positively associated with leaf area, maximum plant height, seed size, and cone size (all slopes > 0, P < 0.05), although individual relationships explained a relatively small proportion of variance ( R² generally < 0.10). Vegetative traits exhibited comparatively larger standardized slopes than reproductive traits. Standardized slopes ranged from 0.026 to 0.103 under dry deposition and from 0.004 to 0.019 under wet deposition. Climate and soil variables jointly accounted for approximately 60–80% of the model-explained variance in plant traits, compared with 4–15% for nitrogen deposition. Dry deposition showed stronger spatial coupling with temperature-related gradients, whereas wet deposition was more closely associated with precipitation-related and vegetation-related gradients. Across China, dry and wet N deposition showed statistically detectable but weak spatial covariation with vegetative and reproductive plant traits. Vegetative traits exhibited comparatively larger standardized associations with deposition than reproductive traits, whereas climate and soil variables accounted for substantially more of the explained variation. Because N deposition was strongly spatially correlated with climatic, edaphic, and vegetation gradients, these observational results should be interpreted as patterns of large-scale co-distribution rather than evidence that N deposition independently or causally drives plant trait differentiation.