Responses of Foliar Nutrient Status and Stoichiometry to Nitrogen Addition in Different Ecosystems: A Meta-analysis

Atmospheric nitrogen (N) deposition alters the cycling of nutrients in terrestrial ecosystems. However, there is limited knowledge regarding how N addition affects foliar nutrients beyond N and phosphorus (P) and their stoichiometry. We conducted a meta-analysis, including 2,004 observations from 134 fertilization studies, to synthesize the effects of N addition on multiple foliar nutrients and stoichiometry in terrestrial ecosystems and to examine their potential controls. Overall, we found that N addition significantly decreased foliar P, potassium (K), calcium (Ca), magnesium (Mg), and calcium:aluminium (Ca:Al) by 3.22%, 7.58%, 9.55%, 5.65%, and 15.17%, respectively, but significantly increased foliar N, Al, N:K, N:Ca, and N:Mg by 19.02%, 6.99%, 21.06%, 27.65%, and 11.33%, respectively. Among the forest ecosystems, foliar N and P exhibited greater changes in temperate or boreal forests, and foliar K, Mg, and Mn showed greater decreases or increases in tropical forests after N addition. Nitrogen addition significantly affected foliar K (-7.55%), Mg (-6.46%), and Al (+6.81%) in forests but not in grasslands. Similarly, foliar K, Mg, and Al showed significant changes in woody plants but not in herbaceous plants. In addition, we found that environmental factors (e.g., ambient N deposition, mean annual precipitation, and soil pH) affected foliar nutrient responses of N, K, and Mg to N addition. In summary, our findings indicate that N addition affects foliar nutrient contents, with the extent of these effects differing among ecosystem type. This is important for understanding and predicting plant growth and nutrient dynamics under N deposition scenarios. Plain Language Summary Foliar nutrients, such as nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), aluminum (Al), manganese (Mn), and iron (Fe), play an important role in plant health and ecosystem function, and an imbalance in these elements affects plant growth. Although atmospheric N deposition has been known to affect foliar N and P contents, much uncertainty exists on how N deposition affects other foliar nutrients and stoichiometry. We conducted a meta-analysis to synthesize the effects of N addition on eight foliar nutrient concentrations (e.g., N, P, K, Ca, Mg, Al, Mn, and Fe) and the stoichiometric ratios of N and these elements in terrestrial natural ecosystems. We found that N addition significantly decreased K, Ca, Mg, and P but increased N, Al, and N:K, N:Ca, and N:Mg across the tested biomes, and these N-induced effects on foliar nutrients varied depending on the ecosystem type. In addition, we found that environmental factors (e.g., soil pH, ambient N deposition, and mean annual precipitation) regulated foliar nutrient responses of N, K, and Mg to N addition. Our findings provide direct evidence that high N deposition affects the nutrient status of plants in terrestrial natural ecosystems, particularly in tropical/subtropical forests. Key Points A meta-analysis was conducted with data from 134 papers to reveal the responses of multiple foliar elements and stoichiometry to N addition Responses of foliar N, P, K, Mg, and Mn to N addition varied depending on the ecosystem type Increases in background N deposition and mean annual precipitation decreased the responses of foliar N, K, and Mg to N addition