Abstract Detail

Ecological Consequences and Mechanisms of Fungal-Fungal Interactions

Mujic, Alija Bajro [1], Kennedy, Peter G. [2], Durall, Daniel M. [3], Spatafora, Joseph W. [1].

On living with family: Factors affecting the vertical distribution of the ectomycorrhizal sister species Rhizopogon vinicolor and Rhizopogon vesiculosus in soil.

Rhizopogon vinicolor and R. vesiculosus (Boletales : Rhizopogonaceae) are sister species that share a sympatric range in the North American Pacific Northwest. These fungi form obligate ectomycorrhizal (EM) associations with a single host tree, Pseudotsuga menziesii (Douglas fir), and occupy a codominant role within the EM fungal community of Northwestern P. menziesii forests. Though they are detected at nearly equal frequencies where they cooccur, these fungi differ dramatically in life history. Rhizopogon vesiculosus produces larger genets, on average, than R. vinicolor that traverse a greater breadth as well as depth of the soil. Vertical partitioning occurs when both species occupy the same column of soil, with R. vinicolor occupying the upper organic horizon and R. vesiculosus occupying the lower mineral horizon. Hypotheses for these distribution patterns include either preference for particular edaphic factors or competitive displacement. To test these two hypotheses, we conducted growth chamber experiments in which the effects of soil strata and competition were experimentally manipulated. Soil was harvested from a site where these Rhizopogon species co-occur, separated into organic (0 – 7.5 cm) and mineral (7.5 – 15 cm) soil strata, and steam sterilized to remove endogenous fungal inoculum. Soil was allocated to pots as either a mix of the two strata, a single strata, or in a configuration mimicking the natural setting. Inoculum of one or both species were introduced into sterilized soil using spores from wild harvested sporocarps. Seeds of P. menziesii were planted into each pot and allowed to grow for seven months. The presence of the two species on EM root tips was detected using PCR amplification of the ITS rDNA region and species-specific microsatellite markers. Our findings suggest that edaphic properties of the two soil strata are not correlated with the observed depth distributions of these two species. In homogenized soils, R. vesiculosus completely excluded R. vinicolor from colonizing seedlings, suggesting the depth partitioning of these two species is more likely related to competitive interactions. However, when similar competitive interactions were run in stratified soil samples, there was greater variation in outcomes, with some colonization by R. vinicolor. This latter result suggests that while strata may not affect the fundamental niche breadth of either species, it may facilitate species coexistence by changing local competitive outcomes. Collectively, our results provide the first experimental evidence showing that biotic interactions interact with edaphic properties to drive the vertical depth partitioning patterns observed among EM fungi.

1 - Oregon State University, Department of Botany and Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331-2902, USA
2 - University of Minnesota , Plant Biology, 1445 Gortner Ave., 250 Biological Science Center, St. Paul, MN, 55108, United States
3 - University of British Columbia, Biology, 3333 University Way, Science Building, Kelowna, BC, V1V 1V7, Canada

Keywords:
Rhizopogon
Pseudotsuga
Competition
Ectomycorrhizae
Fundamental niche
edaphic properties.

Presentation Type: Symposium or Colloquium Presentation
Session: SY4
Location: Auditorium/Kellogg Hotel and Conference Center
Date: Tuesday, June 10th, 2014
Time: 3:30 PM
Number: SY4006
Abstract ID:134
Candidate for Awards:None