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Assessing Two Diagnostic Methods for Enumeration of Nitrate Reducing and Denitrifying Bacteria in Soil‐plant Root Associations
Author(s) -
Volz M. G.
Publication year - 1977
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1977.03615995004100020032x
Subject(s) - denitrifying bacteria , nitrate , weed , bacteria , horticulture , agronomy , biology , enumeration , chemistry , botany , nitrogen , denitrification , ecology , mathematics , organic chemistry , combinatorics , genetics
Most probable number (MPN) determinations were made of NO 3 ‐ reducing‐ and denitrifying bacteria in soil samples taken at time of crop harvest from fallow sites and from root zones of fertilized field plots of tomato ( Lycopersicon esculentum L.), soybean ( Glycine max L. Merr.), or corn ( Zea mays L.) plants cultivated in pure stand or in association with nutsedge ( Cyperus esculentus L.), a competitive weed. Diagnostic methods utilized were inoculated Difco NO 3 ‐ broth and Giltay's medium (citrate‐nitrate‐asparagine + mineral salts), incubated with and without the exclusion of atmospheric O 2 , respectively. The NO 3 ‐ broth method usually yielded both numerically larger and significantly different (5% level) MPNs for NO 3 ‐ reducers (5 of 7 cases larger, 3 significant) and denitrifiers (6 of 7 cases larger, 3 significant) from a given soil inoculum when compared with identical enumerations performed with Giltay's medium. When selected soil inocula were incubated anaerobically in Giltay's medium, MPNs of neither NO 3 ‐ reducers nor denitrifiers were increased significantly as compared with the aerobic procedure. Therefore, larger MPNs of soil NO 3 ‐ reducers and denitrifiers observed when NO 3 ‐ broth is utilized are probably more due to improved nutritional environs than to ambient oxygen status. As a result, a more complete estimate of these soil bacterial populations, especially those from the vicinity of plant roots is thought to be obtained using the NO 3 ‐ broth procedure.