MANIPULATION OF BACTERIA, FUNGI AND PROTOZOA BY BIOCIDES IN LODGEPOLE PINE FOREST SOIL MICROCOSMS: EFFECTS ON ORGANISM INTERACTIONS AND NITROGEN MINERALIZATION

Abstract

Biocides were applied singly and in combination to determine their effect on target and nontarget microorganisms in mineral soil from a lodgepole pine forest and to determine microbial interaction effects on N mineralization. Soil was sterilized and reinoculated with field populations of bacteria, fungi and protozoa. Streptomycin (a bactericide), fungizone (a saprophytic fungicide), chloroform (reduces protozoa and a portion of the bacteria and fungi), a combination of cygon (an acaricide), carbofuran (an insecticide-nematicide) and chloroform and a combination of streptomycin and fungizone were used. Reduction of bacteria produced the same decreases in N immobilization and increases in soil inorganic N in forest soil as observed previously in grassland soil. Further, reduction of fungi decreased N mineralization. Chloroform reduced protozoa to below detection limits, reduced bacterial populations 2- to 10-fold, but only reduced fungal populations by twofold. Despite reductions in both bacteria and fungi, NH+4-N increased similarly to streptomycin treatments where only bacteria were reduced. When fungal populations increased after a reduction in bacterial populations, inorganic N concentrations increased. However, when fungal populations were reduced, bacterial populations did not increase, suggesting that bacteria do not compete with fungi for substrates. Key words: Microbial ecology, N mineralization, streptomycin, amphotericin B, chloroform, pesticide effects, lodgepole pine soil