Elevated atmospheric CO2 alters root symbiont community structure in forest trees

Changes in below-ground ectomycorrhizal (ECM) community structure in respon se to elevated CO2 and balanced nutrient addition were investigated in a 37 -yr-old Picea abies forest. Trees in whole-tree chambers were exposed to factorial combinations of ambi ent/elevated CO2 (700 ppm) and fertilization (+/-). ECM fungal community st ructure was determined in 1997 and 2000 using a combination of morphotyping and molecular analyses. Samples were taken both from chambers and from ref erence trees receiving the same fertilization treatments but without chambe rs. Significant effects on ECM community structure were found in response to el evated CO2. Neither elevated CO2 nor fertilization altered species richness ; however, there was considerable variation among samples, which may have m asked treatment effects on individual species. After 3 yr, the effects of e levated CO2 on community composition were of the same magnitude as those se en after 15 yr of fertilization treatment. Our results show that increasing atmospheric CO2 concentrations affect the community structure of root symbionts colonizing forest trees. The potentia l effects of altered ECM community structure on allocation and turnover of carbon and nutrients within forest ecosystems are discussed.