Examining the role of competition in ectomycorrhizal interactions
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Examining the role of competition in ectomycorrhizal interactions. Peter Kennedy NPER post-doctoral fellow - UC Berkeley [email protected] Competition:. A major factor structuring natural assemblages. Typically highly asymmetric. Competitive hierarchies are common.

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Examining the role of competition in ectomycorrhizal interactions

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Examining the role of competition in ectomycorrhizal interactions

Examining the role of competitioninectomycorrhizal interactions

Peter Kennedy

NPER post-doctoral fellow - UC Berkeley

[email protected]


Competition

Competition:

A major factor structuring natural assemblages

  • Typically highly asymmetric.

  • Competitive hierarchies are common.

  • Order of arrival can significantly effect outcome.

Generalizations


Research questions

Research questions

1. How is ECM competition structured in the field?

  • What are main mechanisms by which it occurs?

    2. Are there competitive hierarchies among ECM fungi?

  • If so, are competitive dominants also better symbionts?


Study system

Study System

Point Reyes National Seashore, CA

Bishop Pine (Pinus muricata)

Rhizopogon spp.


Mycorrhizal abundances at pt reyes

Mycorrhizal abundances at Pt. Reyes

ECM Species

Forest type

Young

Mature

(0-10 yr)

(40-60 yr)

Rhizopogon occidentalis

Rhizopogon vulgaris

Rhizopogon salebrosus

Rhizopogon evadens

Rhizopogon is a dominant colonizer of seedlings in post-fire and primary

successional settings.


Lab study results

Lab Study Results

  • Timing of colonization differed considerably between species

  • Strong asymmetry and priority effects were

  • observed

  • Inoculation curves very similar between species

Kennedy and Bruns (2005), New Phyt. 166: 631-638.


Field competition experiment

Field competition experiment

  • Two species: R. salebrosus (RS) and R. occidentalis (RO)

  • Treatments: no inoculum, single species, two species

  • 20 replicates/treatment at three sites

  • Harvested seedlings after 5 and 10 months

  • Analyzed ECM root tips with real-time PCR


Results fungi

R. occidentalis

0.4

RO single-species

a

RO two-species

a

0.35

a

0.3

a

a

a

0.25

log (x+1) DNA yield

0.2

0.15

0.1

0.05

0

D ranch

PPP 1B

PPP 2B

R. salebrosus

a

a

a

b

a

b

Results: Fungi

  • Highly asymmetric

  • (i.e. mostly all or nothing)

  • Priority effect again observed

  • lab and field results = good correspondence


What about the few co colonized seedlings

What about the few co-colonized seedlings?

a

a

R. salebrosus is not always the competitive inferior!


Results plants

Results: Plants

Being mycorrhizal is very important in terms of growth, but ECM competition has little effect


What about the natural pattern

ECM Species

Forest type

Young Burned

Mature Unburned

(0-10 yr)

(40-60 yr)

Rhizopogon occidentalis

Rhizopogon vulgaris

Rhizopogon salebrosus

Rhizopogon evadens

Abundances based on Gardes and Bruns (1996), Horton et al. (1998), Taylor and Bruns (1999), Baar et al.(1999), and personal observation (T. Bruns).

What about the natural pattern?


Types of ecm competition

Types of ECM Competition

Time

Exploitation

Interference


Competitive hierarchy experiment

Competitive hierarchy

R. vulgaris

R. salebrosus

R. occidentalis

R. evadens

R. evadens

R. vulgaris

R. occidentalis

Competitive hierarchy experiment

  • Four species: Rhizopogon vulgaris (RV), R. salebrosus (RS), R. evadens (RE), R. occidentalis (RO)

  • All pair-wise and one three-way combination (RO/RV/RS)

  • Spores of competitors added at the same time (106 spores/species)

  • 10 replicates/treatment grown for 8 months (growth chamber)

  • Harvested all seedlings and root tips analyzed with real-time PCR

Competitive intransivity

R. salebrosus


Results a competitive hierarchy

RV

RS

RO

RE

R. vulgaris

(RV )

+

+

+

(10/10)

(7/10)

(10/10)

_

+

+

R. salebrosus

(RS)

(0/10)

(9/10)

(10/10)

_

_

+

R. occidentalis

(RO)

(3/10)

(1/10)

(10/10)

_

_

_

R. evadens

(RE)

(0/10)

(0/10)

(0/10)

Results: A Competitive Hierarchy!


What about the plants

a

ab

bc

c

What about the plants?

Seedling biomass

Shoot Nitrogen

a

a

b

b

The best competitors may be the best symbionts


Applications for forestry

Applications for Forestry

  • Mixed species ECM inoculations may not be effective - competitive interactions are strong and highly asymmetical.

  • Differences in timing of spore germination may affect seedling ECM composition - priority effects observed in both lab and field studies.

  • More studies are necessary to determine competitive ability - for Rhizopogon, competitive dominants appear to be the best symbionts.


Acknowledgements

Acknowledgements

  • Sarah Bergemann, Sara Hortal, Tom Bruns

  • Bruns lab members, UC Berkeley

  • Point Reyes National Seashore

  • National Parks Ecological Research Fellowship

  • National Science Foundation


Ongoing experiments

Ongoing experiments

  • Do spore- vs. mycelial-based ECM competition have different outcomes?

  • Can priority effects be reversed by altering the timing of colonization?

  • Does ECM competition occur mainly through direct or indirect interactions?

  • Does spore density and soil heating affect the outcome of ECM competition?


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