T.P. McGonigle, M.H. Miller Applied Soil Ecology 14 2000 147–155 151
with separation of means using Tukey’s test Steel and Torrie, 1980.
3. Results
Shoot dry mass at the end of the experiment Fig. 1a was greater for plants in the U treatment compared
to the D treatment at the two highest inoculum levels. Corresponding values for shoot-P concentration Fig.
1b were higher for plants in the U treatment at all in- oculum levels. Although there was no effect of inocu-
lum density on shoot-N concentration p=0.60 and no interaction with disturbance p=0.27, shoot-N con-
centration was higher p0.001 at 29.4 mg g
− 1
for plants in the U soil, compared to in the U soil where
it was 25.9 mg g
− 1
. Root-length density was not affected by inocu-
lum density or soil disturbance. Overall values mean±s.d.; n=32 at the three-, four-, and five-leaf
Fig. 1. Effect of soil disturbance on a shoot dry mass per plant and b shoot-P concentration at the five-leaf stage of the second
growth cycle, in relation to the percentage of the soil blend that was pasteurized soil. Asterisks indicate where the members of a
pair of means for the undisturbed U and disturbed D treatments were significantly different at the 0.05 probability level; n=4.
Fig. 2. Effect of soil disturbance on the percentage of root length with arbuscules for plants at the two-, three-, four-, and five-leaf
stages in the second growth cycle, and in relation to the percentage of the soil blend that was pasteurized soil. Asterisks indicate where
the members of a pair of means for the undisturbed U and disturbed D treatments were significantly different at the 0.05
probability level; n=4.
stages were 3.7±1.3, 4.1±1.3, and 6.3±0.9 cm
− 3
, respectively.
The inoculum density treatments successfully gen- erated a range of colonization Fig. 2. Arbuscular col-
onization was as high as 39 and 36 in the U treatment at the four- and five-leaf stages in the two soil blends
with the highest inoculum density, but in the two soil blends with the most pasteurized soil the highest ar-
buscular colonization reached was 16 Fig. 2. In general, soil disturbance led to reduced levels of colo-
nization, although some variability was found Fig. 2. The more pronounced effects of disturbance on colo-
nization were seen consistently under the higher, and not the lower, inoculum conditions Fig. 2.
Fig. 3. Biomass carbon in soil following root dusting and removal at the three-, four-, and five-leaf stages in the second growth
cycle, and in relation to the percentage of the soil blend that was pasteurized. Means have been averaged across disturbance
treatments, for which there were no significant effects; n=8.
152 T.P. McGonigle, M.H. Miller Applied Soil Ecology 14 2000 147–155
Soil biomass-C decreased in proportion with in- creases in content of pasteurized soil in the soil blends
Fig. 3, but it was not affected by soil disturbance. Considering each of the inoculum density treatments
separately, soil biomass-C levels were similar at the three-, four-, and five-leaf stages Fig. 3. For the data
as in Fig. 3 but pooled across soil-blend treatments and times, extrapolation gave a biomass carbon value
of 338 mg kg
− 1
for non-pasteurized soil: biomass car- bon mg kg
− 1
=338–2.2107 pasteurized soil , with r
2
= 0.48 and n=96.
4. Discussion
