TABLE 1

Soil fungal responses to elevated CO2 in field experiments and hypothesized mechanisms

EcosystemFungal response to elevated CO2Hypothesized mechanismsReference(s)
Desert shrub, aspen, loblolly pine, scrub oak, tidal marshCellulolytic enzyme diversity increased or showed no response, depending on ecosystemHigher plant cellulose availability with elevated CO2 stimulates cellulose-degrading fungi; fungal community difference between ecosystems reflects differences in soil properties3
Pine forestRelative abundance of ectomycorrhizal fungi, but not species richness, changed with elevated CO2; EM communities grew more dissimilar with elevated CO2Greater fine root biomass with elevated CO2 increased the no. of colonizable sites for EM fungi; also, greater resource availability with elevated CO2 allowed new species to invade5
ChaparralAM fungi shifted from Glomus dominance at low CO2 to Scutellospora and Acaulospora dominance at high CO2; AM hyphal length in bulk soil did not increase with elevated CO2Decreased N availability at elevated CO2 may favor low-N-adapted AM fungal taxa; Collembola increased with elevated CO2 and may have consumed the AM fungal hyphae, reducing apparent CO2 response in their length18, 54
AspenNo effect of elevated CO2 on fungal abundance in phospholipid fatty acid profiles in low-N or high-N soilIn this young, developing ecosystem, the CO2-influenced effect of root inputs on microbial communities appeared negligible compared to the effect of native soil organic matter13
GrasslandAM fungal hyphae increased linearly across a natural CO2 gradientResource balance model: greater aboveground resources (CO2) led plants to allocate more carbon to acquiring belowground resources, through increased mycorrhizal symbiosis53
GrasslandNo effect of elevated CO2 on soil microbial community composition or biomassPlant productivity response to elevated CO2 was reduced compared to that in other studies, resulting in no CO2 response in soil microbial communities71
GrasslandElevated CO2 increased microbial biomass and enzyme activities; elevated CO2 stimulated bacterial biomass but decreased fungal biomassIncreased root production and rhizodeposition with elevated CO2 stimulated microbial biomass and activity; effects of plant species and soil physiochemical properties likely mediate microbial community responses to CO212