Interactive effects of seasonal drought and elevated atmospheric carbon dioxide concentration on prokaryotic rhizosphere communities.

Global change models indicate that rainfall patterns are likely to shift towards more extreme events concurrent with increasing atmospheric carbon dioxide concentration ([CO ]). Both changes in [CO ] and rainfall regime are known to impact above- and belowground communities, but the interactive effects of these global change drivers have not been well explored, particularly belowground. In this experimental study, we examined the effects of elevated [CO ] (ambient + 240 ppm; [eCO ]) and changes in rainfall patterns (seasonal drought) on soil microbial communities associated with forest ecosystems. Our results show that bacterial and archaeal communities are highly resistant to seasonal drought under ambient [CO ]. However, substantial taxa specific responses to seasonal drought were observed at [eCO ], suggesting that [eCO ] compromise the resistance of microbial communities to extreme events. Within the microbial community we were able to identify three types of taxa specific responses to drought: tolerance, resilience and sensitivity that contributed to this pattern. All taxa were tolerant to seasonal drought at [aCO ], whereas resilience and sensitivity to seasonal drought were much greater in [eCO ]. These results provide strong evidence that [eCO ] moderates soil microbial community responses to drought in forests, with potential implications for their long-term persistence and ecosystem functioning.