Changes in soil microbial communities over time resulting from one time application of zinc: a laboratory microcosm study

doi:10.1016/S0038-0717(99)00059-0

Soil Biology and Biochemistry

Volume 31, Issue 10, September 1999, Pages 1455-1465

https://doi.org/10.1016/S0038-0717(99)00059-0 Get rights and content

Abstract

Soil microcosms each consisting of approximately 20 kg soil were set up in the laboratory. Three microcosms were amended with 6000 mg zinc kg⁻¹, a concentration chosen to approximate the quantities of total zinc found at a contaminated field site. Three control microcosms received no zinc amendment. Three pH control microcosms received H₂SO₄, adequate to result in the same pH decrease as occurred in the zinc amended soil. Mean soluble zinc contents were 4660 mg kg⁻¹ (amended soils), 1.08 mg kg⁻¹ (unamended soils), and 2.10 mg kg⁻¹ (pH adjusted soils). Biological community assessments included culturable bacteria (plate counts), microbial biomass (chloroform fumigation), dehydrogenase activity, proportion of zinc resistant bacteria (plate counts on zinc amended agar), and changes in community structure (BIOLOG and phospholipid fatty acid (PLFA) analysis). After 15 d of incubation, zinc amendment resulted in an 87% decrease in viable counts and a 47% decrease in microbial biomass. Dehydrogenase activity decreased by 95%, and the proportion of zinc resistant bacteria increased from 0.08% to 0.75%. Microbial community structure alteration resulting from zinc amendment was indicated by shifts in both BIOLOG metabolic profiles and PLFA profiles. Effects of zinc on PLFA profiles included relative decreases in indicator fatty acids for arbuscular mycorrhizal fungi and actinomycetes. Some adaptation of the microbial communities to the zinc amendment was suggested by the fact that after 420 d incubation there were no significant differences in culturable bacterial populations or microbial biomass of the control and zinc amended systems. However, other microbial properties measured in this study showed that zinc still affected microbial community structure and activity after 420 d. Dehydrogenase activity of the zinc treated communities remained 93% lower than the controls. The percentage of zinc resistant populations was still significantly higher for the zinc treated communities. Similarly, the BIOLOG and PLFA profiles continued to show differences in the structure of the zinc treated and control microbial communities. Effects of zinc on PLFA profiles at day 420 included a relative decrease in an indicator fatty acid for arbuscular mycorrhizal fungi and a relative increase in an indicator fatty acid for fungi. The comparison of PLFA profiles also showed mixed results for several fatty acid indicators for actinomycetes. The pH control treatment showed similar effects on population size and activity as the zinc treatment, although in most cases there was a much stronger effect with the zinc treatment. In addition, the pH treatment caused changes in BIOLOG and PLFA profiles which were different than the changes seen with zinc treatment.

Introduction

Numerous field studies have demonstrated the adverse effects of heavy metal contamination on soil microbial communities (Jordan and LeChevalier, 1975, Baath, 1989, Valsecchi et al., 1995, Giller et al., 1998). Field studies on the effects of heavy metal contamination have often been conducted at sites where the contamination event occurred decades earlier (Pennanen et al., 1996, Kelly and Tate, 1998a). For example, earlier studies assessed the effects of heavy metal contamination on microbial communities from soils in the vicinity of a zinc smelter that has been in operation since 1898 (Kelly and Tate, 1998a). Microbial activity (dehydrogenase activity) and viable population size (plate counts) both decreased in metal contaminated soils. In addition, the population structure of the soil microbial communities was altered by the metal contamination, as indicated by changes in BIOLOG metabolic profiles (Kelly and Tate, 1998a) and phospholipid fatty acid PLFA profiles (Kelly, loc. cit.)

Several of the studies discussed above (Baath, 1989, Pennanen et al., 1996, Kelly and Tate, 1998a; Kelly, loc. cit.) indicated that BIOLOG and the PLFA assays were useful methods for assessing long-term effects of metals on soil community structure. However, at long-term field sites, soil microbial communities have had time to adapt to the stress presented by the elevated metal concentrations (Pennanen et al., 1996). Although comparisons of metal-affected communities and non-metal affected communities at these sites can provide information on the changes that have occurred in the communities as a result of the metal contamination, such studies do not provide information on the time course of these changes. Thus, a more controlled, short-term, experiment is needed to assess the abilities of the BIOLOG and PLFA assays to detect initial population shifts following metal contamination. Accordingly, laboratory-scale soil microcosms were amended with a high concentration of zinc and sampled periodically during a 420 d incubation. The amount of zinc added to the soil microcosms in this study approximated the quantity of total zinc occurring in the soils from the zinc smelter site described above (Kelly and Tate, 1998a). Based on the results from the field study, we hypothesize that major changes in both microbial activity and community structure will initially result from high soil zinc loading and that the maximal effects of the zinc amendment will occur soon after soil amendment. An incubation time of greater than 1 y should be sufficient to show community response and adaptation to zinc amendment. Indicators of microbial community size (plate counts and biomass), activity (dehydrogenase activity), zinc resistance (plate counts on zinc amended agar), and community structure (the BIOLOG Assay and the PLFA Assay) were used to assess the effects of the zinc amendment. The BIOLOG assay allows characterization of entire microbial communities based on the pattern of utilization of 95 different carbon substrates, i.e. the “metabolic profile”. The PLFA assay is used to characterize changes in microbial community structure by evaluating shifts in PLFAs extracted from whole environmental samples. Because different subgroups of microorganisms contain different PLFAs in their cell membranes, shifts in PLFA profiles are indicative of changes in the overall structure of microbial communities (Frostegard et al., 1993a).

Our objectives were (a) to assess changes in soil microbial communities over time after application of a high quantity of zinc, (b) to assess changes in soil microbial communities over time after a significant decrease in pH, and (c) to compare the microbial community changes seen in a controlled laboratory study to changes seen in the field (Kelly and Tate, 1998a; Kelly, loc. cit.).

Section snippets

Microcosms

Nine soil microcosms were set up in the laboratory in April 1996. Each microcosm consisted of a 30.5×40.6×45.7 cm high-density polyethylene tub. Eight equally spaced 13 mm holes were drilled in the bottom of each tub to allow drainage. The bottom of each tub was covered with fiberglass mesh and lined with 2.5 cm of pea gravel. Each tub was filled with 20 kg of air-dried freehold loamy sand (Table 1). Before being put into the tub, the soil was brought to 33.3 kPA moisture content by addition of

Results

The addition of zinc resulted in a significantly higher amount of soluble zinc as compared to the control and pH control microcosms. The mean values for soluble zinc were 1.08 mg kg⁻¹ soil for the control treatment, 2.10 mg kg⁻¹ soil for the pH control treatment, and 4660 mg kg⁻¹ soil for the zinc treatment. There were no significant changes in the amounts of soluble zinc for any of the treatments during the study. The addition of zinc also resulted in a significant decrease in pH compared to

Microcosm soil considerations

Zinc amendment had a strong effect on the size of the microbial communities early in the incubation, as indicated by the viable counts and microbial biomass (Figs. 1(b) and 1(c)). This decrease in microbial populations is accentuated by the fact that populations in the control microcosms were at their highest numbers early in the study. This augmented population density resulted from soil preparation procedures (sieving and mixing) as well as from the amendment of the soils with corn stover.

Acknowledgments

The authors thank Dr Harry Motto, Professor Emeritus of Rutgers, The State University of New Jersey, for his advice and assistance with this project.

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¹: Present address: Department of Civil Engineering, 2145 Sheridan Road, Northwestern University, Evanston, IL 60208, USA.

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Changes in soil microbial communities over time resulting from one time application of zinc: a laboratory microcosm study

Abstract

Introduction

Section snippets

Microcosms

Results

Microcosm soil considerations

Acknowledgments

Science of the Total Environment

Soil Biology & Biochemistry

Soil Biology & Biochemistry

Soil Biology & Biochemistry

Soil Biology & Biochemistry

Soil Biology & Biochemistry

FEMS Microbiology Ecology

Soil Biology & Biochemistry

Microbial community-based measurements to estimate heavy metal effects in soil: The use of phospholipid fatty acid patterns and bacterial community tolerance

AMBIO

Effects of heavy metals in soil on microbial processes and populations (a review)

Water Air and Soil Pollution

Sensitivity of various bacteria, actinomycetes, and fungi to cadmium and the influence of pH on sensitivity

Applied and Environmental Microbiology

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Applied and Environmental Microbiology

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New Phytologist

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Water Air and Soil Pollution