From Disruption to Restoration: Global Impacts of Soil Salinity and Its Mitigation Strategies on Ecosystem Nitrogen Cycling

Salinity impairs soil health by disrupting microbial activity and altering soil physicochemical properties, ultimately undermining ecosystem resilience and productivity. Yet, the effect of salinity and its mitigation strategies on soil nitrogen (N) cycling and plant ammonium and nitrate uptake and N use efficiency is not well established on a global scale. Through a meta-analysis of 3422 paired observations from 309 publications, we found that salinity significantly alters soil N dynamics across multiple pathways. It inhibited the nitrification process by reducing microbial biomass, leading to a substantial accumulation of ammonium (+145%) and nitrite (+203%), while significantly suppressing biological N fixation (-82%). These shifts significantly increased plant uptake of ammonium but reduced that of nitrate and total N, ultimately contributing to a decline in crop yield by 9.5%. Accumulated ammonium in soil also increased ammonia volatilization by 158%. The effect of salinity on soil N availability was context-specific, exhibiting greater effects under high salinity levels, especially in natural ecosystems, arid zones, and alkaline soils. Contrastingly, salinity mitigation treatments led to significant improvements across multiple N pathways. They enhanced soil N pools, including increased biological N fixation and available and total N concentrations. These changes supported greater plant N uptake, resulting in increased N use efficiency and crop yield. However, these benefits were accompanied by a significant increase in nitrous oxide emissions by 80%, indicating a trade-off between environmental impacts and productivity gains. These effects of salinity mitigation treatments on N cycling were more pronounced under the application of organic and mineral fertilizers, as well as crop growth promoters. Collectively, our findings indicate that while salinity appears to impair N cycling by reducing microbial biomass and limiting plant N assimilation, these effects are reversible through mitigation measures. However, further investigation is required to develop salinity mitigation approaches that concurrently minimize nitrous oxide emissions.