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Microbial Biomass Levels in Barren and
Vegetated High Altitude Soils
Ruth E. Ley, David A. Lipson, and
S.K. Schmidt
Microbial biomass generally increases with
organic matter accretion in soils, but little is known about the relative
proportion of specific microbial functional groups that compose the biomass.
We measured the biomass of two microbial functional groups in soils of
a high altitude talus slope (3700 m) in the Colorado Rock Mountains. Talus
slopes are composed of boulders, with occasional patches of soil in the
rock matrix. Because of the severity of the physical conditions, many
soil patches are barren. Carbon inputs to barren talus soils are thought
to be predominantly eolian deposition. The soils we studied all had the
same parent material, aspect and climate, but ranged in soil organic matter
(SOM content from 6 to 250 g kg-1). Total soil C and N, silt,
clay, and SOM all increased linearly as sand content decreased. Using
the substrate-induced growth response (SIGR) assay and a most-probable
number (MPN) assay, we estimated the general microbial biomass (glutamate
mineralizers) and the biomass of a microbial group capable of degrading
more complex carbon compounds (salicylate mineralizers). In vegetated
soils, both groups were positively correlated with SOM. In barren soils,
however, silt content was the best predictor of total biomass, which showed
no trend at all with SOM. In contrast, the relationship between the biomass
of salicylate mineralizers and SOM was the same in vegetated and barren
soils, although it was not significant in barren soils. In addition, the
proportion of salicylate mineralizers in the total biomass was higher
in barren soils than in vegetated soils, which is possibly as a result
of different carbon quality inputs to the soils. This research represents
the first in-depth description of the biology and soil characteristics
of barren high elevation talus soils.
Soil Science Society of Amer. Journal (2001) Vol. 65, No. 1: 111-117