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The nitrogen-15 (15N) natural abundance composition (δ15N) in soils or plants is a useful tool to indicate the openness of ecosystem N cycling. This study aimed to evaluate the influence of the experimental warming on soil and plant δ15N. We applied a global meta-analysis method to synthesize 79 and 76 paired observations of soil and plant δ15N from 20 published studies, respectively. Results showed that the mean effect sizes of the soil and plant δ15N under experimental warming were −0.524 (95 % CI (confidence interval): −0.987 to −0.162) and 0.189 (95 % CI: −0.210 to 0.569), respectively. This indicated that soil δ15N had negative response to warming at the global scale, where warming had no significant effect on plant δ15N. Experimental warming significantly (p) decreased soil δ15N in Alkali and medium-textured soils, in grassland/meadow, under air warming, for a 4–10-year warming period and for an increase of >3 ∘C in temperature, whereas it significantly (p) increased soil δ15N in neutral and fine-textured soils and for an increase of 1.5–3 ∘C in temperature. Plant δ15N significantly (p) increased with increasing temperature in neutral and fine-textured soils and significantly (p) decreased in alkali soil. Latitude did not affect the warming effects on both soil and plant δ15N. However, the warming effect on soil δ15N was positively controlled by the mean annual temperature, which is related to the fact that the higher temperature can strengthen the activity of soil microbes. The effect of warming on plant δ15N had weaker relationships with environmental variables compared with that on soil δ15N. This implied that soil δ15N was more effective than plant δ15N in indicating the openness of global ecosystem N cycling.

The 15N natural abundance composition (δ15N) in soils or plants is a useful tool to indicate the openness of ecosystem N cycling. This study was aimed to evaluate the influence of the global warming on soil and plant δ15N. We applied a global meta-analysis method to synthesize 79 and 76 paired observations for soil and plant δ15N from 20 published studies, respectively. Results showed that the mean effect sizes of the soil and plant δ15N under experimental warming were −0.524 (95 % CI: −0.987 to −0.162) and 0.189 (95 % CI: −0.210 to 0.569), respectively. This indicated that soil and plant δ15N had negative and positive responses to warming at the global scale, respectively. Experimental warming significantly (p 15N in Alkali soil, grassland/meadow, and under air warming, whereas it significantly (p 15N in neutral soil. Plant δ15N significantly (p p 15N. However, the warming effect on soil δ15N was positively controlled by the mean annual temperature, which is related to the fact that the higher temperature can strengthen the activity of soil microbes. The effect of warming on plant δ15N had weaker relationships with environmental variables compared with that on soil δ15N. This implied that soil δ15N tended to be more efficient in indicating the openness of global ecosystem N cycling than plant δ15N.