Effect of co-existing plant specie on soil microbial activity under heavy metal stress

The influence of plant primary compounds on the activity of soil microbial communities under heavy metal stress was studied in a pot-culture field experiment conducted in a green house. Amaranthus spinosus was cultivated in an agricultural soil previously amended in the laboratory with solutions of different trace elements in two separate treatment modes: singly and in combination. Culture-independent metabolism based indices such as the rate of carbon and nitrogen mineralization, microbial biomass carbon and soil basal respiration were monitored fortnightly over a period of six weeks. Result shows that plant detritus have significant modifying effect on soil microbe-metal interactions. Data on microbial and biochemical processes in the respective mesocosms did not vary from control; not even in mesocosms containing very high concentrations of copper, zinc and nickel. The soil microbial biomass carbon and the rate of carbon and nitrogen cycling were not impeded by the respective metal treatment while the respiration responses increased as a result of increase in metabolic activity of the soil microbes. The plant based substrates enabled the soil microflora to resist high metal contamination because of its tendency to absorb large amounts of inorganic cations

Effects of heavy metal pollution on the soil microbial activity

The effects of heavy metals on soil microbial processes were investigated over a period of six weeks. Analytical grade [Sigma] sulphate salts of copper, zinc and nickel were added individually and in combinations to soil samples and incubated in different plastic pots. Samples were taken from the pots forthnightly and the rates of microbial carbon and nitrogen mineralization, microbial biomass carbon and respiration were measured. The results showed the effect of metals on the measured parameters were significant [P<0.05.]. By the 6[th] week postreatment, the rates of carbon accumulated were high in the copper [6.03%] and copper: zinc [5.80%] treatments but low in the nickel and zinc [4.93% and 5.02% respectively]. The rates of nitrogen mineralization were 0.41 and 0.44% in samples treated with copper and copper: zinc compared to 0.22%-0.24% obtained at the beginning of the experiments. Soil microbial biomass carbon declined from average value of 183.7- 185.6 micro g/g before treatment to as low as 100.8 and 124.6 micro g/g in samples treated with copper: zinc and copper respectively. The rate of respiration of the soil microbial populations was equally inhibited by the metals. From an average rate of 2.51-2.56 micro g of C/g respiration of the soil microbes declined to 0.98, 1.08 and 1.61 micro g of C/g in the copper: zinc, copper and zinc treated soils by the end of the experiment. The results suggest additive or synergistic effects of the metals