Ecosystem-specific responses of soil microbial communities to elevated carbon dioxide

Background/Question/Methods

The global atmospheric concentration of CO₂ has been increasing for the last 150 years and is predicted to increase to 550 ppm by the middle of this century.  Some previous studies showed that elevated CO₂ (eCO₂) significantly affected the diversity, composition, structure, and function of soil microbial communities. However, those studies are largely based on a single experimental site or ecosystem. Whether the observed responses are site- or ecosystem-dependent remains unclear. In this study, we examined the response of soil microbial communities under eCO₂ at six different experimental sites or/and ecosystems (BioCON, Duke, ORNL, MaizeFACE, SoyFACE and PHACE).  A total of 110 soil samples with 55 from ambient CO₂ (aCO₂) and 55 from eCO₂ were examined by a comprehensive functional gene array (GeoChip 3.0).  Various statistical methods were applied to detect the effect of eCO₂ and ecosystems on soil microbial communities and their linkages with soil properties.  

Results/Conclusions

Site/ecosystems, CO₂ and their combination significantly (p < 0.05) affected the functional structure and metabolic potential of soil microbial communities with site/ecosystems having much stronger influence (~47%), followed by site/ecosystem and CO2 (~4.1%), and then CO₂ (~1.3%). The abundance of most key functional genes involved in carbon (C), nitrogen (N), phosphorus (P) and sulfur (S) cycling differed significantly among different sites/ecosystems. However, the overall abundance of genes involved in C fixation (Pcc/Acc), C degradation (e.g., pulA, vanA, vdh, mnp, and phenol oxidase genes),  N fixation (nifH), denitrification (e.g., narG, nirS), N reduction (e.g., nasA, nrfA), phosphorus utilization (e.g., phytase genes), and sulfur metabolism (e.g., dsrA/B, sox) generally increased at eCO₂. In addition, such changes in the soil microbial community were closely correlated with soil C and N. This study provides insights into our understanding of soil microbial communities and their feedbacks to terrestrial ecosystems in response to eCO₂.