Soil Microbial Community Response to Hexavalent Chromium in Planted and Unplanted Soil

• Published in: Journal of environmental quality Vol. 36; no. 3; pp. 638 - 645
• Main Authors: Ipsilantis, I, Coyne, M.S
• Format: Journal Article
• Language: English
• Published: Madison American Society of Agronomy, Crop Science Society of America, Soil Science Society 01.05.2007; American Society of Agronomy
• Subjects: Agriculture; Bacteria - drug effects; Bacteria - metabolism; biodiversity; Biomass; Brassica juncea; Chromium; Chromium - pharmacology; Dose-Response Relationship, Drug; Fumigation; Growth rate; Heavy metals; Medical treatment; metal tolerance; Metals; Microbial activity; microbial growth; Microbiology; Microorganisms; Molecular weight; Mustard Plant - drug effects; Mustard Plant - growth & development; Mustard Plant - metabolism; Plant Roots - metabolism; Plant Roots - microbiology; polluted soils; Principal components analysis; Rhizosphere; Soil - analysis; Soil Microbiology; soil microorganisms; soil pH; soil pollution; Soil treatment; Thymidine - metabolism; Tritium
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2005.0438

Theories suggest that rapid microbial growth rates lead to quicker development of metal resistance. We tested these theories by adding hexavalent chromium [Cr(VI)] to soil, sowing Indian mustard (Brassica juncea), and comparing rhizosphere and bulk soil microbial community responses. Four weeks after the initial Cr(VI) application we measured Cr concentration, microbial biomass by fumigation extraction and soil extract ATP, tolerance to Cr and growth rates with tritiated thymidine incorporation, and performed community substrate use analysis with BIOLOG GN plates. Exchangeable Cr(VI) levels were very low, and therefore we assumed the Cr(VI) impact was transient. Microbial biomass was reduced by Cr(VI) addition. Microbial tolerance to Cr(VI) tended to be higher in the Cr-treated rhizosphere soil relative to the non-treated systems, while microorganisms in the Cr-treated bulk soil were less sensitive to Cr(VI) than microorganisms in the non-treated bulk soil. Microbial diversity as measured by population evenness increased with Cr(VI) addition based on a Gini coefficient derived from BIOLOG substrate use patterns. Principal component analysis revealed separation between Cr(VI) treatments, and between rhizosphere and bulk soil treatments. We hypothesize that because of Cr(VI) addition there was indirect selection for fast-growing organisms, alleviation of competition among microbial communities, and increase in Cr tolerance in the rhizosphere due to the faster turnover rates in that environment.