Monday, August 3, 2009
Exhibit Hall NE & SE, Albuquerque Convention Center
Background/Question/Methods While a wealth of information is available on the effect of non-native earthworms on soil biogeochemical cycling, few studies have addressed how earthworm invasion might affect plants, especially tree recruitment. We have established a series of field manipulations to test possible mechanisms by which earthworms can affect mycorrhizal fungi and thus indirectly tree seedling growth. Earthworms may: 1./ physically disrupt mycorrhizae through soil mixing and burrowing, 2. change nutrient availability by altering litter quality and quantity, and 3. shift the composition of the soil fungal community. In 75 and 150+ yr old deciduous forests we established 60 1x1 m field enclosures to manipulate earthworm density (by repeated electroshocking), species composition, and litter quality. We examined responses in earthworm communities, soil respiration, enzyme activity, and microbial community abundance and composition. Soil enzymes and quantitative PCR provide complementary information about the soil microbial community and allow us to separate direct and indirect effects of earthworms on seedling growth and survival.
Results/Conclusions We consistently found 10-100% more earthworms and greater biomass under tulip poplar compared to beech leaf litter additions. Soil respiration rates were also higher under tulip poplar under leaf litter and higher in the old forests by 30-40%.
In a 6-week field mesocosm experiment we found that some enzymes (β-Glucosidase and polyphenol oxidase) responded positively to mixing and disruption by earthworms while N-acetyl-glucosaminidase and polyphenol oxidase increased in response to fertilization with earthworm casts, suggesting different aspects of earthworm activity affects different microbial functions. Q-PCR showed that bacteria increased and ectomycorrhizal fungi (Russula and Tomentella) decreased in response to disruption and fertilization, both in absolute quantity and relative to total fungi, suggesting earthworm effects on ectomycorrhizal fungi were direct, rather than indirect through effects on plant hosts. Long-term monitoring of seedling survival and growth (ongoing) will show the how these changes belowground are linked to the aboveground community.
Results/Conclusions We consistently found 10-100% more earthworms and greater biomass under tulip poplar compared to beech leaf litter additions. Soil respiration rates were also higher under tulip poplar under leaf litter and higher in the old forests by 30-40%.
In a 6-week field mesocosm experiment we found that some enzymes (β-Glucosidase and polyphenol oxidase) responded positively to mixing and disruption by earthworms while N-acetyl-glucosaminidase and polyphenol oxidase increased in response to fertilization with earthworm casts, suggesting different aspects of earthworm activity affects different microbial functions. Q-PCR showed that bacteria increased and ectomycorrhizal fungi (Russula and Tomentella) decreased in response to disruption and fertilization, both in absolute quantity and relative to total fungi, suggesting earthworm effects on ectomycorrhizal fungi were direct, rather than indirect through effects on plant hosts. Long-term monitoring of seedling survival and growth (ongoing) will show the how these changes belowground are linked to the aboveground community.
