Effects of non-native earthworms on mycorrhizal fungi and tree seedling growth Melissa McCormick Katalin Szlavecz Brenda Nieto Lijun Xia Dennis Whigham

"On a global basis...the two great destroyers of biodiversity are, first habitat destruction and, second, invasion by exotic species” - E.O. Wilson ethanzuckerman.com Image from The Nature Conservancy’s Wildland Invasive Species Task Force appomattoxnews.com

Invasive Species An invasive species is “an alien species whose introduction does, or is likely to cause, economic or environmental harm or harm human health” In the U.S. there are nearly 6,600 non-native species Invasive species have influenced all U.S. ecosystems The current annual environmental, economic, and health-related costs of invasive species exceed those of all other natural disasters combined (estimated at $122 Billion in 2000). Ehrenfeld 1997, Cox 1999, Rossman 2001, USGS 2010, Pimentel et al. 2000.

Invaders under our feet Below-ground biological invasions have gone largely unnoticed until recently: Apart from a few familiar cases of Argentine fire ants (Solenopsis invicta) in Oceania and North America, the Formosan termite (Coptotermes formosanus) in South Africa and the southeastern United States, and the New Zealand flatworm (Arthurdendyus triangulatus) in the British Isles. Photos courtesy Chi-han Chang

Exotic earthworms around the world Hendrix et al. 2008. Pandora’s box contained bait

Exotic Earthworms in North America After last Ice Age many unutilized opportunities Native Introduced James, 1995 Reynolds,1995

Earthworm invaders Introduced earthworms now occur in every biogeographic region in all but the driest or coldest habitat types on Earth. Hendrix et al. 2008

Earthworms GOOD? BAD?

Earthworm species differ Amynthas hilgendorfi- Asian Lumbricus rubellus - European Eisenoides loennbergi - Native Bouche 1977 Lumbricus friendi - European Octolasion lacteum - European

PLANT FUNGUS Mycorrhizas Definition Mycorrhizal Function INTRODUCTION Definition A mycorrhiza is a symbiotic association between a fungus and a plant root. Mycorrhizas Source: Smith & Read 1997 Mycorrhizal Function A bi-directional exchange of nutrients PLANT FUNGUS Carbon Soil Nutrients

Conifers, Oaks, Hickories, Beeches, Birches, Chestnut ECM Mycorrhizae have been identified in fossils of plants as early as 400mya and are considered crucial to plants adapting to life on land (Taylor et al. 1995, Taylor & Krings 2005, Krings et al. 2007). Nearly all forest plants are mycorrhizal...except for some invasive species. Conifers, Oaks, Hickories, Beeches, Birches, Chestnut ECM Tulip poplar, Sweetgum, Maples, Ashes, Elms, Sycamore AM http://www.paintthelight.net/BotanyProject/Activities/adaption_plants.htm

How do we look at fungi in the soil? Extract DNA from soil There are LOTS of fungi in the soil! Up to 150 species in 0.5g of soil. 2 samples 15cm apart may share only 25% of their species. We use specific PCR primers to look only at the DNA from the fungi we are interested in. Soil core Fungal DNA

Quantifying fungi in the soil:

A field experiment Smithsonian Environmental Research Center (SERC), Edgewater, MD 48 plots (1mx1m) were trenched to 50 cm depth, lined with mesh screen and backfilled.

Manipulating earthworms Earthworms were removed from half of the plots by repeated electroshocking.

Tree seedlings and leaf litter Leaf litter was added (beech on one side and tulip poplar on the other) and seedlings planted in the plots.

Measured variables / expectations Soil Processes: Decomposition ↑ Respiration ↑ Abundance of microbial taxa (qPCR): Mycorrhizal fungi ECM (Tomentella, Russula) ↓ AM ↓ Tree seedling performance Growth (biomass) ? Plant mycorrhizal colonization ↓

Decomposition: Decomposition was greater in forests with earthworms if mesh size allowed earthworms to access leaf litter. * * Szlavecz et al. In press

Respiration: Respiration was higher in plots with earthworms, especially on the side with tulip poplar leaf litter. Mature Forest Successional Forest

Mycorrhizal fungi were less abundant in plots with earthworms Site p<0.001 EW p=0.08 Site x EW p=0.06 Site p<0.001 Site x EW p=0.08 Site p<0.001 EW p=0.05 0.14 AM fungi Tomentella Russula 0.12 0.10 0.08 (ng DNA/g dry soil/total quantified DNA) 0.06 Proportional Abundance 0.04 0.02 0.00 Old forest Young forest Old forest Old forest Young forest Young forest Site No Earthworms Earthworms

Log above-ground biomass Tree seedling growth Alex Binck Oaks and beeches grew less in plots with earthworms. Maples grew more. no EW EW Oak ↓ Beech ↓ Maple ↑ old young -4.0 -3.5 -3.0 -2.5 -2.0 P=0.07 Tulip ↑ old young -2.00 -1.25 -0.50 0.25 1.00 old young -2.00 -1.50 -1.00 -0.50 0.00 -1.5 P=0.07 P=0.09 old young Log above-ground biomass (mean g + se) -2.0 -2.5 -3.0 -3.5 Few Tulip poplar seedlings survived in old forests and none in old forest plots without earthworms. Forest Age

Key Conclusions Earthworm activities affected mycorrhizal fungi and tree seedlings: Mycorrhizal fungi were less abundant in plots with earthworms. Earthworms affected growth of red oak and beech but not maple or tulip poplar. Earthworm effects on tree seedlings differed with species: Changes to nutrients affected early successional trees (+). Changes to mycorrhizal fungi affected late successional trees (-).

What does this mean for our forests? Forest composition may change: Early successional trees may be better able to use nutrients made available by earthworms and may dominate longer. Invasive plants may increase. Forest floor habitat for ground-nesting birds may decrease. Keep non-native earthworms out of forests where they haven’t already invaded: Increase awareness of bait release, moving plants, compost (especially vermicomposting), and mulch.

Acknowledgements Funding: Field Help: USDA-CSREES 2007-35320-18375 NSF (EAR-0748442) Smithsonian Women’s Committee Field Help: Jay O’Neill Alex Binck Matt Sievers Scott Pitz Helen Huang Natalie Bray Chi-Han Chang Mike Bernard