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

## TL;DR

The study shows that the effects of individual stressors on urban soils change when combined with other factors, suggesting that removing harmful stressors is more effective than adding single ones.

## Contribution

The novel approach of comparing single-factor addition with subtraction in multi-stressor contexts reveals how global change factors interact unpredictably.

## Key findings

- Removing stressors from a multi-factor context generally improves soil properties and biological processes.
- Resource-related factors enhance microbial activity individually but not in multi-factor scenarios.
- The combined effects of stressors often differ from their individual impacts, emphasizing the need for targeted mitigation.

## 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.

Urban soils are exposed to numerous human-driven stressors that can interact in unpredictable ways. This study concludes that the impact of adding one factor does not correspond to the impact of removing it from a set of interacting stressors.