The Effects Of Aboveground Plants, Geochemical Elements And Battery Contamination On Characteristics Of Soil Microbial Communities

Soil microbes play an important role in many critical ecosystem processes, including energy flow, nutrient cycling, decomposition of organic matter, and the maintenance of soil fertility, etc. Soil microbes are influenced by aboveground vegetation, soil geochemical elements and edaphic pollutants such as battery waste. Aboveground vegetation can influence the characteristics of the soil microbial community through providing suitable habitats and food sources. Some nutritious geochemical elements provide nutrients for the growth of soil microbes, but some toxic geochemical elements including heavy metals in high concentrations have the adverse effects on soil microbial community. Furthermore, more and more battery wastes have been discarded randomly into soil and were badly endangering the health of soil microbes. The changes in magnitude, structure, and activity of soil microbial community due to the above factors may have implications for microbe-mediated processes. Measures of microbes responding to the above factors could be expected to give insights into restoration of native ecosystems and selections from sensitive microbial indicators of soil contamination.In this study, 16 sites were selected every kilometer from northwest to southeast along the beeline through Jinan city of China in August, 2005. Plant species composition and the projective covers of all plant species in each site were determined. Diversity indices were calculated from plant species and their projective covers. Six soil cores were randomly taken from the top 10 cm of the profile in each site and mixed and homogenized thoroughly. Concentrations of As, B, Cd, Co, Cr, Cu, F, Hg, Mn, Mo, Ni, P, Pb, V, Zn, Se, N, S, SiO₂ Al₂O₃, Fe₂O₃, MgO, CaO, Na₂O and K₂O were determined using standard analytical techniques as described in the "Specification for multi-purpose regional geochemical survey (1: 250000)", total element (TE) level for each site was calculated according to the 25 elements. As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, V and Zn were regarded as toxic elements and heavy metals, total pollution (TP) level for each site was calculated according to the above 11 elements. Bacteria, fungi, actinomycetes, nitrogen-fixing bacteria, ammonium oxidizing bacteria, nitrifying bacteria, denitrifying bacteria, and cellulose decomposing bacteria were enumerated using the cultivation techniques. Microbial biomass and community structure were assessed by phospholipid fatty acid (PLFA) technique. Community-level physiological profiles (CLPPs) and microbial function diversity were assessed by Biolog microplate technique. The above studies were used to understand the effects of the aboveground vegetations and geochemical elements on soil microbial communities. Furthermore, microcosm soils were treated with 0, 0.32, 3.2 and 8 g·kg^-1 battery powders, respectively. Microbial biomass and respiration were measured after 15, 30, 45, and 60 days of the treatment, and CLPPs and microbial function diversity were assessed by Biolog microplate technique after 60 days of the treatment. These studies were used to evaluate the effects of the battery waste on the microbial communities in soil.The results showed that plant diversity had little discernible effect on the most of numbers of culturable microrobial populations and microbial function diversity. The numbers of culturable microrobial populations and function diversity were very high in soybean field, which indicates that legumes can significantly enhance the growth and activity of soil microbes. In this study, PLFA profiles distinguished the soil microbial community structures beneath natural vegetations from those beneath artificial vegetations, which indicates that human activity has a significant effect on the structure of soil microbial community.There were no significant correlations between the most of geochemical elements and the numbers of the microbial populations. However, the concentration of Cd had significant positive correlation to the number of culturable bacteria (R = 0.72, P < 0.01), the number of culturable fungi (R = 0.52, P < 0.05), the number of culturable actinomycetes (R = 0.66, P < 0.01), the number of culturable nitrogen-fixing bacteria (R = 0.66, P < 0.01), and the number of culturable cellulose decomposing bacteria (R = 0.80, P < 0.01). The concentration of N was positively correlated with the number of culturable bacteria (R = 0.57, P < 0.05), the number of culturable actinomycetes (R = 0.67, P < 0.01), the number of culturable nitrogen-fixing bacteria (R = 0.56, P < 0.05), and the number of culturable cellulose decomposing bacteria (R = 0.61, P < 0.05). These results indicate that the addition of Cd and N in low concentrations can significantly influence the growth and reproduction of soil microbes. There were no significant correlations between the most of geochemical elements and the function diversity of soil microbial community. However, the concentration of Co had significant negative correlation to microbial function diversity with respective correlation coefficients of -0.54 for Shannon 5 and -0.53 for Shannon H (P < 0.05 in both cases). There was significant positive correlation between the concentration of Cr and AWCD value (R = 0.52, P < 0.05). These results indicate that Co in low concentrations retard the function of soil microbial community while Cr in low concentrations stimulate the function of soil microbial community.The battery pollution had different effects on soil microbial biomass, respiration, and catabolic capability. Addition of the battery powder inhibited soil microbial biomass but enhanced its respiration and catabolic capability. These results suggested that, in unfavorable conditions, soil microorganisms were able to divert energy from anabolic processes to maintenance requirements for survival. Interestingly, on day 60 after the treatment, no significant differences were found in the microbial biomass between the four treatments. However, a significant difference was still detected in the microbial respiratory quotients between the high level treatment and the control. These results indicate that, over time, soil microorganisms can recover the same biomass as the control, and also suggest the possibility that, the recovery of the microbial respiratory quotient needs more time than that of microbial biomass, or may not even be achieved. Furthermore, the CLPPs showed that battery pollution still had a significant effect on soil microbial community structure 60 days after the treatment commenced, this indicates the permanence of the effects of battery contamination on soil microbial communities.Many geochemical elements had significant effects on cellulose decomposing bacteria. The number of culturable cellulose decomposing bacteria had significant correlation to the concentrations of As, Cd, Cr, P, N, TE, and TP. This indicates that the cellulose decomposing bacteria are more sensitive than other microbial populations and can be used as a possible indicator in monitoring soil pollution and soil fertility. When the correlations between the geochemical elements and microbial biomass were analyzed, no significant correlations between most of geochemical elements and the biomasses or ratios of microbial populations were found. However, the concentration of Mn Pb Se and S had significant positive correlation to the ration of GP to GN, and their Correlation coefficients were 0.51, 0.50, 0.50 and 0.56 respectively (P < 0.05 in all cases). This indicates that the ratio of two microbial populations is usually more sensitive to environmental factors than one microbial population. The ration of GP to GN could be sensitive microbial indicator of Mn Pb Se and S bioavailability. In this study, the inhibition caused by battery pollution on the microbial biomass gradually became weaker during the incubation period until it disappeared at the last sampling time. Therefore, the microbial biomass might not be a sensitive indicator of battery stress on bioavailability. The microbial respiratory quotient and catabolic capability were significantly higher in the high level treatment than the other treatments during the whole incubation period. The Biolog profile of the high level treatment could be differentiated from those of the other treatments at the last sampling time. Therefore, microbial respiratory quotient and Biolog parameters are sensitive indicators of battery stress on bioavailability and may be promising indicators in monitoring soil pollution caused by used batteries.In this study, when the microbial communities of 16 sampling sites were clustered by principal components analysis, PLFA profiles could discriminate microbial community structures beneath natural vegetations from those beneath artificial vegetations while Biolog profiles could not discriminate the CLPPs of the 16 microbial communities. The concentration of Cd had significant positive correlation to the numbers of many microbial populations, while no significant correlation to microbial function diversity. The concentration of Co had no significant correlation to the numbers of microbial populations, while significant negative correlation to microbial function diversity. These results indicate that aboveground plants and geochemical elements can influence the characteristics of the soil microbial community through providing suitable habitats, food and energy sources for soil microbes. However, the shifts of different soil microbial parameters driven by environmental factors are inconsistent. Therefore, the combination of several approaches is recommended for accurately describing the characteristics of microbial communities in many respects.In summary, aboveground vegetations influence the soil microbial community magnitude, structure, and functional diversity through difference of plant diversity, legumes, and human disturbance. The present result shows that there was no discernible effect between plant diversity and soil microbial parameters. Legumes could significantly enhance soil microorganisms in many respects including the number of cultural microorganisms, microbial biomass, and microbial functional diversity. Disturbance could significantly affect soil microbial community structure. The study of the effects of aboveground vegetations on soil microorganisms has implications for restoration of native ecosystems. Geochemical elements in low concentrations can promote the production and growth of soil microbes, while may retard the function of soil microbes. Battery waste had serious adverse effects on the soil microbial community, through reducing microbial biomass, increasing microbial activity and changing the structure of the microbial community. Although soil microbial biomass is capable of recovery under the stress of battery contamination, a long period of damage of battery contamination on soil microbial communities still exists. The number of cellulose decomposing bacteria and the ratio of biomasses of two microbial populations are promising microbial indicators in monitoring soil pollution. Microbial respiratory quotient and Biolog parameters are sensitive indicators of battery stress on bioavailability. The study of the effects of geochemical elements and battery contamination on soil microbes has implications for selecting sensitive indicators in monitoring soil pollution.