Mineralización de nitrógeno en suelos contaminados: indicador poco confiable de la toxicidad de metales

Soil contamination with metals constitutes a significant global environmental challenge. Microbial processes, such as nitrogen mineralization, are frequently employed as indicators of soil health and potential metal toxicity. This study examined the relationship between soil metal contamination, particularly copper, and nitrogen mineralization rates in 87 agricultural soils from copper-mining impacted regions of central Chile. Given the measured metal concentrations in the soils and established toxicity thresholds for microorganisms, copper was expected to exert substantial toxicity on soil microbial communities, while the effects of other metals were anticipated to be less pronounced. However, our results revealed that the rate of nitrogen mineralization was primarily influenced by soil physicochemical properties, such as soil organic matter content, clay content, and pH, rather than by copper concentrations. In the studied soils, nitrate nitrogen was the dominant form of mineral nitrogen. Further analysis of individual nitrogen forms (ammonium – NH₄⁺, nitrite – NO₂^-, and nitrate – NO₃^-) supported these findings for total mineral nitrogen (i.e., the sum of N-NH₄⁺, N-NO₂^-, and N-NO₃^-). In summary, the findings of this study suggest that nitrogen mineralization may not be a reliable indicator of copper toxicity in contaminated soils.