ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

Effects of Seasonal Changes on the Distribution of Ectomycorrhi zae
Among Soil Fractions
Seasonal changes affected both quantity and the distribution of ectomycorrhi zal
root tips among the various soil organic matter components (fig. 9). The greatest
numbers occurred during the spring, when they were concentrated in soil humus.
Smaller numbers occurred during the rest of the growing season. Most were concen-
trated in the soil-wood during the dry season of the year on the Coram subalpine
fir site (Harvey and others 1978). Similarly, the re1 ative number of ectomycorrhizal
root tips in soil-wood from the six experimental sites were much greater on the
dry sites than on the moister ones (fig. 10). Thus, a greater proportion of the
relatively small amounts of ectomycorrhizal tips on harsh, dry sites (fig. 8)
were concentrated in the soil wood. This is a strong indication that soil-wood
influences productivity on dry sites (Harvey and others 1979).
Although these data emphasize the importance of soil-wood on dry sites, a
substantial proportion of ectomycorrhizal activity occurred in this substrate
even on the very moist sites. When data from a1 1 sites and all seasons were
analyzed together, soil wood proved to be the most important substrate for ectomy-
corrhizae in the northern Rocky Mountains, followed by soil humus, and then the
first 2 in (5 cm) of mineral soil. The latter was a transitional layer between
the humus and the mineral soil base, and had relatively high organic matter
content (8-12 percent as determined by loss-on-ignition).
Figure lo.-- Percentage of ectomycorrhizae in soiZ-mod smpZes &ing the
smer dry season on the s