Edaphic and climatic factors control the response of nutrient-cycling enzyme activity to common heavy metals in soils

Soil enzymes, which are crucial catalysts in soil nutrient cycling, are sensitive to heavy metals and metalloids (HMMs). Yet, the mechanistic understanding of soil enzyme activities (EAs) response to HMMs is still only rudimentarily known. By analyzing 1989 paired observations from 145 studies investigating HMMs effect on 14 enzymes, we found that HMMs decreased the activity of β-D-glucosidase (-25.3 %), cellulase (-10.3 %), urease (-26.8 %), protease (-22.5 %), phosphatase (-21.0 %), arylsulphatase (-37.0 %), catalase (-19.2 %) and dehydrogenase (-33.1 %), with natural ecosystems being more severely affected than croplands. This decrease in EAs was mainly due to decreased microbial biomass content and abundance and increased microbial metabolic quotient. However, HMMs increased polyphenol oxidase activity (82.2 %), possibly because HMMs can serve as cofactors or activators for polyphenol oxidase and/or because microbes produced it as a defense mechanism under stress. The response ratio of EAs is driven by cation exchange capacity (CEC) and dominantly influenced by soil organic carbon (SOC), clay, and bulk density (BD). Increased CEC, SOC and clay content and decreased BD reduced the negative effect of HMMs on EAs. Climate impact on the response ratio of EAs was mediated through soil properties. Our analysis provides a more holistic representation of EAs response to HMMs, offering comprehensive insights into the ecological consequences of HMMs on ecosystem functioning.