Da. Klein et Mw. Paschke, A soil microbial community structural-functional index: the microscopy-based total/active/active fungal/bacterial (TA/AFB) biovolumes ratio, APPL SOIL E, 14(3), 2000, pp. 257-268
In most studies of fungal-bacterial communities in soils, single-value indi
ces such as fumigation-extraction (FE) of microbe-derived organic carbon, m
easures of specific microbial cell chemical constituents, or activity-relat
ed measures have been used. These widely used single value indices, however
, do not provide information on the physical structure of the filamentous f
ungal and bacterial community in a soil. The filamentous fungi, considered
as indeterminate organisms, have a variable and changing hyphal network, mo
st of which is devoid of cytoplasm. To meet this need for a direct integrat
ed measure of the physical characteristics of the indeterminate fungi and t
heir associated bacteria, a microscopy-based microbial biovolumes ratios ap
proach is suggested. To provide this information, the total and active biov
olumes of both the filamentous fungi and bacteria are assessed by microscop
y. To normalize these responses, the ratio of total to active (TA) fungal p
lus bacterial biovolumes is divided by the ratio of the active fungal to ba
cterial biovolume (AFB), to yield the total/active/active fungal/bacterial
(TA/AFB) biovolumes ratio. This approach has been used to analyze data from
recently-cultivated early successional (ES) and uncultivated late successi
onal (LS) sites at a shortgrass steppe of northeastern Colorado, where cont
rol plots were compared with those receiving mineral nitrogen amendments, u
sing samples taken during the summer of 1995. The TA/AFB ratio index showed
distinct and significant decreases in response to soil disturbance which r
eflected the decreased hyphal lengths present in these disturbed soils. The
se changes were not detected by the use of FE-based extractable carbon meas
urements. The TA/AFB ratio also showed significant positive correlations wi
th indices of plant community development and mineral nitrogen, especially
in the plots not amended with N. This TA/AFB ratios index should be able to
provide information on the physical structure of the indeterminate filamen
tous fungi and associated soil bacteria for use in the assessment of soil q
uality, health and resiliency. (C) 2000 Published by Elsevier Science B.V.
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