Ectomycorrhizal fungi introduced with exotic pine plantations induce soil carbon depletion

Exotic pine plantations are promoted for their presumed capacity to provide a net sink of atmospheric C. Millions of hectares worldwide will be subjec ted to conversion into plantations during the next decades. However, pine i ntroductions are known to result in a marked depletion of soil C, a phenome non which has remained unexplained. We studied plantations in paramo grassl ands of Ecuador, where the effect of the exotic introduction of radiata pin es (Pinus radiata) and their accompanying ectomycorrhizal fungi can be stud ied in isolation from other ecosystem disturbances. We suggest that ectomyc orrhizal fungi can extract C previously accumulated by paramo grasslands ba sed on (a) a drastic simplification of the ectomycorrhizal community shown by direct DNA identification, (b) a loss of up to 30% soil C within <20 yea rs of plantation, (c) stable C isotope values in fungal fruitbodies which a re closer to grassland than pi tie values, and (d) radiocarbon dating of fr uitbodies indicating relatively old C sources for fruitbody formation. Spec ies number in the ectomycorrhizal guild drops to only three fungal species per plantation compared to approximately 100 in comparable native pine stan ds. Our results provide evidence for a dynamic role of ectomycorrhizal fung i in soil C processing, and question the strategy of introducing pine plant ations as a general solution to reduce mounting atmospheric CO2 levels. (C) 2001 Elsevier Science Ltd. All rights reserved.