EARTHWORM (LUMBRICUS-RUBELLUS AND APORRECTODEA-CALIGINOSA) EFFECTS ON CARBON FLUX IN SOIL

Effects of earthworm activities on litter and soil C flux were studied in a laboratory incubation experiment using two types of isotopic tracers and two earthworms with different ecological strategies-Lumbricus rubellus, an epigeic species, and Aporrectodea caliginosa, an endogeic species. The soil was prelabeled with C-14. Dry sorghum [Sorghum bicolor (L.) Moench] leaves labeled with C-13 were applied to the soil surface. Activity of both earthworm species significantly (P < 0.001) enhanced total C efflux (479 +/- 8 [standard error], 483 +/- 4, and 395 +/- 5 mg C jar(-1) for L. rubellus, A. caliginosa, and the control, respectively) and significantly (P < 0.05) reduced total surface soil microbial biomass (251.7, 205.2, and 312.1 mg C kg(-1) soil for L. rubellus, A. caliginosa, and the control, respectively) during the 30-d incubation. Activity of A. caliginosa also reduced subsurface soil microbial biomass. The epigeic earthworms assimilated significantly more C-13 from the Litter and significantly less C-14 from the soil than the endogeic species. In the absence of earthworms, C-14 in the soil was translocated into the surface litter, as shown by a 15.5-fold increase in C-14 enrichment in the surface litter by the end of the experiment. This translocation of soil C into the litter was significantly reduced by earthworm activities (155.43, 121.11, and 240.58 kBq kg(-1) litter for L. rubellus, A. caliginosa, and the control, respectively), possibly due to disruption by earthworms of fungal-hyphal connections between litter and soil. These interactions between earthworms and soil microbial processes have important implications for soil C turnover.