Er. Ingham et Wg. Thies, CHANGES IN RHIZOSPHERE MICROFLORA AND MICROFAUNA 10 YEARS FOLLOWING DOUGLAS-FIR LIVE TREE INJECTION WITH CHLOROPICRIN OR METHYLISOTHIOCYANATE, Canadian journal of forest research, 27(5), 1997, pp. 724-731
Live Douglas-fir (Pseudotsuga menziesii (Mirb.) France) trees were inj
ected in 1981 with chloropicrin or methylisothiocyanate (MITC) in an e
ffort to control laminated root rot caused by Phellinus weirii (Murr.)
Gilb. Soil samples were collected in 1991 from around structural root
s 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, th
e number of protozoa (flagellates, ciliates, and amoebae), and the num
ber and types of nematodes were evaluated, Active fungal biomass was r
educed by both chemicals as compared with noninjected trees 10 years a
fter application Both active and total bacterial biomass were also sig
nificantly 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 gr
eater around MITC-treated roots, while predatory nematode numbers were
lower, than around control roots. Reduced bacterial and fungal biomas
s around MITC-treated trees may be the result, therefore, of increased
feeding by nematodes, and thus MITC-treated trees may benefit from mo
re rapid nutrient-cycling rates but may suffer more pest damage from r
oot-feeding nematodes as a result of the chemical application. Since m
any organism groups were reduced around roots of chloropicrin- and MIT
C-treated trees, this suggests possible impacts related to reductions
in nutrient cycling rates and production of plant-available N around t
hese trees.