Simulation of growth and flux of carbon and nitrogen through earthworms

Earthworms contribute to carbon and nitrogen cycling directly through the a ccumulation (consumption), storage (assimilation) and turn over (respiratio n, excretion, mortality) of nutrients from their tissues. An energetics-bas ed model was designed to describe the flows of C and N through three compon ents: litter, earthworm, and byproducts pools. Litter C and N pools contain ed insoluble nutrients that were consumed by earthworms. A portion of consu med C and N were assimilated from the earthworm gut and used for growth and maintenance of earthworm tissue. Earthworm byproducts included C and N def ecated in earthworm casts as well as C and N released from earthworm tissue through respiration and excretion. The effect of litter quality, soil temp erature and soil moisture content on C and N fluxes through earthworms were simulated. Tissue C accumulation was validated using growth data and N flu xes were validated with N-15-nitrogen consumption, assimilation and excreti on data from laboratory studies with Aporrectodea tuberculata (Eisen). Sens itivity analysis indicated most uncertainty in the function describing the effect of soil temperature on litter C and N consumption. C and N storage a nd turn over from earthworm tissues was greatest when the litter C:N ratio was 10 and declined as the litter C:N ratio increased to 30. Tissue C and N accumulation was affected strongly by soil temperature and moisture, and o ptimal conditions for earthworm growth were at 15 degrees C and 30 % (w/w) soil moisture content. Further work involving the addition of a dynamic pop ulation structure to the model and validation with data from field studies is underway to determine the contribution of earthworms to ecosystem-level fluxes of C and N.