A meta-analysis of soil extracellular enzyme activities in response to global change

The crucial biogeochemical processes such as carbon and nutrient cycling are increasingly altered at the eco-system scale by global environmental changes. Although soil extracellular enzyme activities (EEAs) play a critical role in biogeochemical processes, the global patterns of soil EEAs in a changing world remain elusive. Here, we synthesized eight EEAs involved in carbon (C), nitrogen (N) and phosphorus (P) acquisition in response to seven global change factors based on 132 peer-reviewed papers. Our results showed that elevated CO2 concentration had no significant effects on soil EEAs. Nitrogen addition stimulated C-acquisition (9.1%) and P acquisition (9.9%) EEAs, but suppressed oxidase activity (-6.8%). Phosphorus addition decreased P-acquisition EEA (-19.8%), while combined N and P addition increased C-acquisition EEA (30.7%). Moreover, decrease in precipitation dramatically suppressed oxidase activity (-47.2%), increase in precipitation marginally stimulated N-acquisition EEA (16.7%), while warming significantly decreased oxidase activity (-10.9%) and had minor positive effect on hydrolytic enzymes. Overall, our results provide some evidence (with exceptions) for the resource allocation theory of microbial enzyme production, and indicate that EEAs are generally more sensitive to nutrient addition than to atmospheric and climate change. We have shown that global environmental changes can alter EEAs, which have implications for soil carbon storage, nutrient cycling, and plant productivity. Further research is needed to elucidate the underlying mechanisms driving the responses of EEAs to global change and to collect data from particularly non-forest ecosystems (e.g., wetland, tundra and desert) and global-change drivers (other than N addition) that lack of EEA data. Our synthesis of the responses of soil enzyme activities to global change drivers can be used to develop better representations of microbial processes in ecosystem and earth system models.