PARENT SESSION
Contributed Oral Session 166: Soil Communities and Plant-Root Interactions
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 522 A, Level 5, Palais des congrès de Montréal

Rhizosphere disturbance influences fungal colonization and subsequent community development on dead fine roots.

Fisk, Melany^*,1, Sobieraj, Jim¹, Costello, Andria², Fahey, Timothy³, ¹ Appalachian State University, Boone, NC, USA² Syracuse University, Syracuse, NY, USA³ Cornell University, Ithaca, NY, USA

ABSTRACT- Our understanding of forest ecosystem function would benefit from better knowledge of the ecology of organisms involved in fine root decay, given the importance of fine root turnover to ecosystem carbon flux. Existing measurements of fine root decomposition rates suggest that disruptions of the rhizosphere community change the decay process in fine roots. These observations lead us to hypothesize that the rhizosphere community structure on living roots influences the subsequent colonization and community development following root death. We tested this hypothesis with rhizosphere disturbance experiments in root windows at the Hubbard Brook Experimental Forest, NH. We generated dead fine roots of known age by drilling through root windows to kill root networks. In half of the windows we moved roots into a sieved soil medium to disrupt the rhizosphere microbial community that had developed over the root lifetime. We sampled fragments from dead roots repeatedly over 13 months to explore patterns of fungal species composition over time after root death. Fungi were cultured from fragments of each root sample and identified by RFLP analysis of the ITS region of the nuclear rDNA genes, followed by sequencing of the dominant RFLP groups. We found that disturbance of the root rhizosphere prior to initiation of decomposition changed the dominant fungal taxa, the distribution of dominance within the community, and the temporal development in the culturable fungal community. Fifty-five RFLP groups were detected in a total of 360 samples. Thirty of these groups occurred in control roots and 40 occurred in disturbance roots, with 15 groups common to both treatments. Control root communities were dominated by 2 - 3 species, shifting from Cylindrocarpon sp. in early samples to Mortierella sp. in later samples. Dominance was more even and communities more diverse for disturbance roots. Disturbance roots were dominated by Trichoderma sp., Cylindrocarpon sp, 2 other species of Mortierella, and Verticilium sp. Our results show that fungal community development over time is influenced by early colonization, suggesting that the rhizosphere community that develops over the lifetime of the root may impact subsequent colonization by decomposer fungi.

Key words: fine roots, decomposer fungi, fungal community