Regulation of the biomass and activity of soil microorganisms by microfauna

Microcosm experiments showed that the microbial biomass and the respiration activity in soil were regulated by nematodes. Depending on nematode number and plant residue composition, the trophic activity of nematodes can eithe r stimulate or inhibit microbial growth and respiration as compared to soil containing no nematodes. The stimulating effect was observed when nitrogen -free (starch) or low-nitrogen (wheat straw, C : N = 87) organic substrates were applied. Inhibition occurred when a substrate rich in nitrogen (alfal fa meal, C : N = 28) was decomposed and the nematode population exceeded th e naturally occurring level. A conceptual model was developed to describe t rophic regulation by microfauna (nematodes) of the microbial productivity a nd respiration activity and decomposition of not readily decomposable organ ic matter in soil. The stimulating and inhibiting influence of microfauna o n soil microorganisms was not a linear function of the rate of microbial co nsumption by nematodes. These effects are largely associated with the induc ed change in the physiological state of microorganisms rather than with the mobilization of biogenic elements from the decomposed microbial biomass.