PARENT SESSION
Monday, August 7, 5:00-6:30 pm
Poster Session 2 - Invasive species
Exhibit Hall, Ballroom Level, Cook Convention Center

Carbon and nitrogen dynamics in soils with native and exotic earthworms determined with stable isotopes.

Camp, Dana^*,1, Callaham, Mac¹, O'Brien, Joseph¹, Bennett, Susan¹, Hendrix, Paul², ¹ Southern Research Station, Athens, GA² Institute of Ecology, Athens, GA

ABSTRACT- Little is understood of the ecology of earthworms in forests of the southeastern US. Even less is known of interactions between native North American species and introduced European species. We conducted a growth chamber study using ¹³C labeled white oak (Quercus alba) seedlings and ¹⁵N labeled oak litter in mesocosms (10 cm dia., 20 cm depth) to examine the effects of native and exotic earthworms on plant growth, C and N dynamics. Three different earthworm species of different ecological strategies and origins were used in an incomplete factorial design to examine the movement of C and N in soil, plant, and earthworm biomass pools. These species included: native endogeic (Diplocardia silvicola), exotic endogeic (Octolasion tyrtaeum), and exotic epigeic (Lumbricus rubellus). Six experimental groupings were established: 1) Native endogeic alone; 2) Exotic endogeic alone; 3) Exotic epigeic alone; 4) Native endogeic with exotic endogeic; 5) Native endogeic, exotic endogeic, and exotic epigeic together; 6) No earthworms (control). On two sample dates (at three weeks and six weeks) mesocosms were destructively sampled for: soil above 5 cm, soil below 5 cm, coarse root material, fine root material, leaves, stems, and earthworm tissue. Results from the earthworm tissue analysis indicated no difference in the ¹³C signatures of any worms in any combination. On the other hand, earthworm tissue analysis for ¹⁵N signatures indicated strong differences between species in resource use. In single species pots, Lumbricus rubellus exhibited the greatest level of enrichment with ¹⁵N signatures reaching nearly 200 ‰. The pots with two endogeic species together revealed a possibly competitive interaction between native and exotic endogees with O. tyrtaeum (non-native) having the largest ¹⁵N signature (mean signature of 56 ‰ for O. tyrtaeum vs. 30‰ for D. sylvicola). In pots with the three species mix, the endogeic species (both native and exotic) took up less ¹⁵N than when in competition with only one another, and L. rubellus took up more ¹⁵N than when grown in isolation. Plant tissue and soil data for ¹³C and ¹⁵N will also be presented.

Key words: invasive species, earthworms, oak hickory forest