Global change factors differ in effect when acting alone and in a multi-factor background.

Abstract

The presence of multiple global change factors affects most ecosystems. Urban soils face stressors like heat, drought, road salt, nitrogen deposition, surfactants, and microplastics. Given that combined factors of global change have shown unpredictable effects, we here ask which individual factors have particularly negative effects in multifactorial contexts. We explore this through a subtractive design, comparing single-factor treatments (addition) to treatments where a specific factor is removed (subtraction). The results vary from predominantly negative, positive, to mixed effects. However, removing these factors from a multi-factor context generally improves soil properties and biological processes. Resource related factors enhance microbial activity individually but show no such benefit in multi-factor scenarios. Our findings highlight that the combined effects of factors often differ from their individual impacts. In restoration, priority should be given to mitigating factors with the strongest negative influence in multi-stressor contexts, rather than targeting those with significant isolated effects.