Changes in rhizosphere microflora and microfauna 10 years following Douglas-fir live tree injection with chloropicrin or methylisothiocyanate
1997
Ingham, E.R. | Thies, W.G.
Live Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees were injected in 1981 with chloropicrin or methylisothiocyanate (MITC) in an effort to control laminated root rot caused by Phellinus weirii (Murr.) Gilb. Soil samples were collected in 1991 from around structural roots 0.5, 1, and 2 m from the base of injected or noninjected trees. The activity of fungi and bacteria, total fungal and bacterial biomass, the number of protozoa (flagellates, ciliates, and amoebae), and the number and types of nematodes were evaluated. Active fungal biomass was reduced by both chemicals as compared with noninjected trees 10 years after application. Both active and total bacterial biomass were also significantly lower around roots of chloropicrin- and MITC-treated trees, as were flagellate numbers. The number of bacterial-feeding nematodes was decreased around roots of chloropicrin-treated trees, while other nematode-feeding groups were not changed. The number of root-feeding, bacterial-feeding, and fungal-feeding nematodes were significantly greater around MITC-treated roots, while predatory nematode numbers were lower, than around control roots. Reduced bacterial and fungal biomass around MITC-treated trees may be the result, therefore, of increased feeding by nematodes, and thus MITC-treated trees may benefit from more rapid nutrient-cycling rates but may suffer more pest damage from root-feeding nematodes as a result of the chemical application. Since many organism groups were reduced around roots of chloropicrin- and MITC-treated trees, this suggests possible impacts related to reductions in nutrient cycling rates and production of plant-available N around these trees.
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