Biological indicators of copper-induced stress in soil

[摘要] ENGLISH ABSTRACT:The concentrations of copper (Cu) in vineyard soils of the Western Cape range from 0.1to 20 ppm. However, more than 160 tons of the fungicide copper oxychloride areannually being sprayed on these vineyards. This has raised concerns that Cu mayaccumulate in these soils, resulting in a negative impact on the soil biological processes,especially since the soils in the Western Cape are slightly acidic, making Cu more mobileand available for soil organisms than would have been the case in alkaline soils.The goal of the initial part of this study was therefore to identify those soil microbialcommunities indigenous to the Western Cape, which are most susceptible to Cu-inducedstress as a result of the addition of copper oxychloride. These potential bioindicators ofCu-induced stress were first searched for in uncultivated agricultural soil fromNietvoorbij experimental farm. Consequently, a series of soil microcosms was preparedby adding various concentrations of Cu as a component of copper oxychloride, to each ofeight aliquots of soil: 0 (control), 10, 20, 30, 40, 50, 100, 500 and 1000 ppm. Theresulting concentrations of exchangeable Cu in these microcosms were found to be 2(control), 12,23,34,42,59, 126,516 and 1112 ppm. Selected microbial communities ineach microcosm were subsequently monitored over a period of 245 days. It was foundthat the culturable microbial numbers did not provide a reliable indication of the effect ofCu on community integrity. However, analyses of terminal-restriction fragment lengthpolymorphism (T-RFLP) community fingerprints and especially analyses of the wholecommunity metabolic profiles, revealed that shifts in the soil microbial communities tookplace as the Cu concentration increased. Direct counts of soil protozoa also revealed thatthe addition of Cu to the soil impacted negatively on the numbers of these eukaryotes.To confirm these findings in other soil ecosystems, the impact of copper oxychloride onwhole community metabolic profiles and protozoan numbers were investigated in soilsfrom Koopmanskloof commercial farm and Nietvoorbij experimental farm. Thesepotential bioindicators were subsequently monitored in a series of soil microcosmsprepared for each soil type by adding the estimated amounts of 0 (control), 30, 100 and1000 ppm Cu as a component of copper oxychloride to the soil. The results confirmedthe fmdings that elevated levels of copper impact negatively on the metabolic potentialand protozoan numbers of soil.Consequently, it was decided to investigate a combination of protozoan counts andmetabolic profiling as a potential bioindicator for Cu-induced stress in soil. Datacollected from all the microcosms containing exchangeable Cu concentrations rangingfrom 1 ppm to 1112 ppm was used to construct a dendrogram using carbon sourceutilization profiles in combination with protozoan counts. It was found that themicrocosms grouped into clusters, which correlated with the concentration ofexchangeable Cu in the soil. Under the experimental conditions used in this study, thecombination of protozoan counts and metabolic profiling seemed to be a reliableindicator of Cu-induced stress. However, this bioindicator must be further investigated inother soil types using other types of stress inducing pollutants.In addition to the above fmdings it was also found that the numbers of soil protozoa wasparticularly susceptible to Cu-induced stress in soils with a low soil pH. This is inagreement with the fmdings of others on the bio-availability of heavy metals in low pHsoils. In these soils, nutrient cycling as a result of protozoan activity, may therefore beparticularly susceptible to the negative impact of copper to the soil.

[发布机构] Stellenbosch University