Fig. 6

a Factors contributing to the decreasing tree foliar N, P, K, S and Mg concentrations and b a meta-analysis of the effects of experimentally elevated atmospheric CO₂ concentrations (using both FACE and OTC methodologies) on the N, P, K, Mg and Ca concentrations and the N:P ratio of green mature leaves for all types of vegetation. a Plot of the temporal contribution of the predictor variables on N, P, K, S and Mg concentrations and the N:P ratio (Ca concentration did not change significantly; see Fig. 2). The models (see Supplementary Table 1) suggest that increasing CO₂ is the main and only contributor to the decreases in N, P, K and S concentrations. The temporal variations of the predictors are shown in Supplementary Fig. 12. Error bars indicate standard errors. Units are ppm for CO₂, kg ha⁻¹ y⁻¹ for S and N deposition and °C for temperature. See Methods for information about the methodology used to calculate the contributions. (*), P < 0.1; *P < 0.05; **P < 0.01; ***P < 0.001. b Meta-analysis of published studies (353, 297 and 684 studies for N and P concentrations and the N:P ratio, respectively). See references in Supplementary material for Fig. 6b.