1. Examining the role of competition in ectomycorrhizal interactions Peter Kennedy NPER post-doctoral fellow - UC Berkeley pkennedy@berkeley.edu

2. Competition: Typically highly asymmetric. Competitive hierarchies are common. Order of arrival can significantly effect outcome. A major factor structuring natural assemblages Generalizations

3. 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?

4. Study System Point Reyes National Seashore, CA Bishop Pine ( Pinus muricata ) Rhizopogon spp.

5. Mycorrhizal abundances at Pt. Reyes Forest type YoungMature Rhizopogon occidentalis Rhizopogon vulgaris Rhizopogon salebrosus Rhizopogon evadens (0-10 yr)(40-60 yr) ECM Species Rhizopogon is a dominant colonizer of seedlings in post-fire and primary successional settings.

6. 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.

7. 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

8. Results: Fungi a a a b b a 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 D ranch PPP 1B PPP 2B log (x+1) DNA yield RO single-species RO two-species a a a a a a R. occidentalis R. salebrosus Highly asymmetric (i.e. mostly all or nothing) Priority effect again observed lab and field results = good correspondence

9. What about the few co-colonized seedlings? R. salebrosus is not always the competitive inferior! a a

10. Results: Plants Being mycorrhizal is very important in terms of growth, but ECM competition has little effect

11. What about the natural pattern? Forest type Young BurnedMature Unburned Rhizopogon occidentalis Rhizopogon vulgaris Rhizopogon salebrosus Rhizopogon evadens (0-10 yr)(40-60 yr) ECM Species Abundances based on Gardes and Bruns (1996), Horton et al. (1998), Taylor and Bruns (1999), Baar et al.(1999), and personal observation (T. Bruns).

12. Types of ECM Competition ExploitationInterference Time

13. Competitive hierarchy experiment R. salebrosus Competitive intransivity 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 (10 6 spores/species) 10 replicates/treatment grown for 8 months (growth chamber) Harvested all seedlings and root tips analyzed with real-time PCR R. occidentalis R. evadens R. vulgaris R. salebrosus Competitive hierarchy R. occidentalis R. evadens R. vulgaris

14. Results: A Competitive Hierarchy! R. occidentalis (RO) R. vulgaris (RV ) R. salebrosus (RS) R. evadens (RE) RVRSRORE + ++ (0/10) (3/10) _ _ _ __ _ ++ + (10/10)(7/10)(10/10) (9/10) (10/10) (1/10) (0/10)

15. What about the plants? Seedling biomassShoot Nitrogen a ab bc c a a b b The best competitors may be the best symbionts

16. 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.

17. Acknowledgements Sarah Bergemann, Sara Hortal, Tom Bruns Bruns lab members, UC Berkeley Point Reyes National Seashore National Parks Ecological Research Fellowship National Science Foundation

18. 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?