PARENT SESSION
Organized Oral Session 26: From microbes to ecosystems: How do we really make the connections?
Organizer(s): J Schimel and S Frey
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 510a, Level 5, Palais des congrès de Montréal

Ectomycorrhizal fungi and elevated CO₂: Community response and ecosystem consequences.

Parrent, Jeri^*,1, Morris, William¹, Vilgalys, Rytas¹, ¹ Duke University, Durham, NC

ABSTRACT- Increased atmospheric CO₂ concentrations may affect ectomycorrhizal fungi (EMF) at multiple ecological scales. Individual species may experience changes in abundance and frequency of mycorrhizal formation; changes in EMF colonization and competitive abilities may result in altered community composition and diversity; ecosystem level consequences derived from community shifts may further result in changes to soil mycorrhizal biomass and nutrient acquisition. In this study we examined how an atmosphere enriched in CO₂ may influence EMF species and community dynamics, and their ecosystem level consequences at FACTS-I research site in Duke Forest, NC. To assess changes in EMF relative frequency, community composition and diversity, both on fine roots and in bulk soil, we collected mycorrhizas and mycelium from ambient and elevated CO₂ plots, and determined EMF species identity from these samples by sequencing the ITS rDNA gene region using fungal specific primers. Total fungal biomass and EMF biomass were also estimated using ergosterol and PLFA in total soil and ingrowth cores, respectively. 72 species were detected from mycorrhizal samples; the three most abundant species, two Russula and one Tylospora species, represented over 30% of all root tip samples. The most abundant species, Russula sp. G, was abundant in all plots and showed no difference between CO₂ treatments, while the second most common species, Tylospora sp. B, showed lower relative frequency in elevated CO₂ plots (mean rel. freq. ambient = 0.147 ± 0.05; mean rel. freq. elevated = 0.055 ± 0.022). Community composition overlapped between root tip and ingrowth core samples, but several species that were abundant in cores were rarely encountered as mycorrhizas, suggesting incongruence between colonization and foraging abilities. Overall community diversity was higher in elevated CO₂ plots, likely due to an increase in occurrence of rare species in elevated plots. However, net nitrogen mineralization was negatively correlated with EMF diversity, and elevated CO₂ amplified this effect. Soil ergosterol concentrations mirrored EMF diversity results, highlighting the dominance of EMF in this soil fungal community, and the importance of considering EMF hyphal biomass when examining C storage and C dynamics associated with increased CO₂.

Key words: mycorrhizae, CO₂, fungal ecology, ITS sequencing