, Volume 187, Issue 2, pp 309-320

Effects of elevated [CO2 ] at the community level mediated by root symbionts

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This review examines the effects of elevated [CO2] on plant symbioses with mycorrhizal fungi and root nodule bacteria, with emphasis on community and ecosystem processes. The effects of elevated [CO2] on the relationships between single plant species and root symbionts are considered first. There is some evidence that plant infection by and/or biomass of root symbionts are stimulated by elevated [CO2], but growth enhancement of the host seemingly depends on its degree of dependence on symbiosis and on soil nutrient availability. Second, the effects of elevated [CO2] on the relationships between plant multispecies assemblages and soil, and likely impacts on above-ground and belowground diversity, are analysed. Experimental and modelling work have suggested the existence of complex feedbacks in the responses of plants and the rhizosphere to CO2 enrichment. By modifying C inputs from plants to soil, elevated [CO2] may affect the biomass, the infectivity, and the species/isolate composition of root symbionts. This has the potential to alter community structure and ecosystem functioning. Finally, the incorporation of type and degree of symbiotic dependence into the definition of plant functional types, and into experimental work within the context of global change research, are discussed. More experimental work on the effects of elevated [CO2] at the community/ecosystem level, explicitly considering the role of root symbioses, is urgently needed.