AbstractBackgroundRecent studies demonstrated that warming and elevated carbon dioxide (CO2) indirectly affect the soil microbial community structure via plant root exudates. However, there is no direct evidence for how the root exudates affect soil microbes and how the compositions of root exudates respond to climate change.ResultsThe results showed that warming directly decreased biomass of soil-borne bacteria and fungi forAcacia mearnsiiDe Willd but it did not impact soil microbial community forEucalyptus urophylla S.T. Blake. In contrast, elevated CO2had strong direct effect on increasing soil microbial biomass for both plant species. However, plant roots could significantly increase the secretion of antibacterial chemicals (most probable organic acids), which inhibited the growth of bacteria and fungi in elevated CO2environment. This inhibitory effect neutralized the facilitation from increasing CO2concentration on microbial growth.ConclusionsWe concluded that climate change can directly affect microorganisms, and indirectly affect the soil microbial community structure by changes in composition and content of plant root exudates.