A meta-analysis of the effects of nitrogen additions on base cations: Implications for plants, soils, and streams

The dominant base cations (BC; i.e., Ca2+, Mg2+, K+, and Na+) are important in buffering soil and water acidity in both terrestrial and aquatic ecosystems. Ca2+, Mg2+, and K+ are also important in many plant physiological functions. Because BC availability is affected by changes in the nitrogen (N) cycle, we conducted a meta-analysis of previously published data to determine if N fertilization alters the availability of BC in terrestrial and stream ecosystems across biomes. We include data from 107 independent studies published in 62 different articles, taking a holistic perspective on BC by examining their responses to added N in plant foliage, bulk soil, soil solution, and stream water. Our results suggest N fertilization may accelerate BC loss from terrestrial ecosystems over time periods less than five years. We found that N additions resulted in an overall 24% decrease in the availability of exchangeable Ca2+, Mg2+, and K+ in the bulk soil of boreal forest, temperate forest, and grassland biomes. Collectively, responses of BC in boreal forest, temperate forest, tropical forest, and grassland biomes increased following N fertilization by about 71% in soil solution and 48% in stream waters. Additionally, BC responses in foliage decreased in boreal forest and temperate forest biomes following N additions over time periods less than five years, but there were no significant changes over longer time periods. Despite large short-term shifts in BC responses following N additions, we did not find evidence of widespread negative impacts on ecosystems over time periods greater than five years. This analysis suggests effects of N addition on the availability of exchangeable BC may diminish over time. Although the effects on BC can be substantial over periods less than five years, there is little available evidence that N fertilization has had large-scale detrimental effects on the availability of BC needed for plant growth within terrestrial or aquatic ecosystems.

► Meta-analysis including 107 independent studies.
► Concentrations of dominant base cations increase in soil solution and stream water following N additions.
► Base cations decrease in bulk soil and plant foliage following N additions but only among studies shorter than five years.
► No significant changes in foliar base cation concentrations among studies five years or longer.
► No evidence that N additions have had large-scale detrimental effect on base cation availability.