Rhizopogon spore bank communities within and among California pine forests

Abstract

In this study we examine the distribution of Rhizopogon species in spore banks from five California pine forests. Four of the forest sites were discontinuous populations of Pinus muricata and a fifth was a Pinus ponderosa stand in Sierra National Forest. Rhizopogon species were retrieved by bioassaying the soils with pine seedlings followed by isolation of axenic cultures from individual root tips with typical Rhizopogon ectomycorrhizal morphology. The cultures were screened by ITS-RFLP and all unique patterns were sequenced. These sequences then were compared with those derived from identified sporocarp material. Bioassaying proved to be an efficient way to bring Rhizopogon species into culture. Approximately 50% of the pots contained ectomycorrhizal tips with Rhizopogon-like morphology, and axenic Rhizopogon cultures were obtained from half these pots. Our results showed that Rhizopogon spores usually are well distributed within local forest areas, while there is significant structuring of species at the regional scale. Spore longevity and homogenization by soil and water movement might explain their distribution within local forest areas, while the regional pattern might be explained by limited long distance dispersal or climatic and edaphic differences.

• bioassay
• community structure
• ectomycorrhiza
• ITS
• Pinus muricata
• RFLP
• sequencing

We wish to thank Martin Bidartondo and Lisa Grubisha for providing access to their Rhizopogon sequences beforePUBLICation and for comments on drafts of this manuscript, Jenny Tan and Sermed Naaman for help in the laboratory and Lee Taylor for collecting the Santa Barbara samples. The Danish Natural Science Research Council to R. Kjøller and NSF grant DEB 9815262 to T.D. Bruns provided partial financing of this study.