Greenhouse gas emissions from a Cu-contaminated soil remediated by in situ stabilization and phytomanaged by a mixed stand of poplar, willows, and false indigo-bush

Phytomanagement of trace element-contaminated soils can reduce soil toxicity and restore soil ecological functions, including the soil gas exchange with the atmosphere. We studied the emission rate of the greenhouse gases (GHGs) CO₂, CH₄, and N₂O; the potential CH₄ oxidation; denitrification enzyme activity (DEA), and glucose mineralization of a Cu-contaminated soil amended with dolomitic limestone and compost, alone or in combination, after a 2-year phytomanagement with a mixed stand of Populus nigra, Salix viminalis, S. caprea, and Amorpha fruticosa. Soil microbial biomass and microbial community composition after analysis of the phospholipid fatty acids (PLFA) profile were determined. Phytomanagement significantly reduced Cu availability and soil toxicity, increased soil microbial biomass and glucose mineralization capacity, changed the composition of soil microbial communities, and increased the CO₂ and N₂O emission rates and DEA. Despite such increases, microbial communities were evolving toward less GHG emission per unit of microbial biomass than in untreated soils. Overall, the aided phytostabilization option would allow methanotrophic populations to establish in the remediated soils due to decreased soil toxicity and increased nutrient availability.

Bioavailability and biological effect of engineered silver nanoparticles in a forest soil

The extensive use of silver nanoparticles (SNPs) as antimicrobial in food, clothing and medicine, leads inevitably to a loss of such nanomaterial in soil and water. Little is known about the effects of soil contamination, in particular, on microbial cells, which play a fundamental ecological role. In this work, the impact of SNPs on forest soil has been studied, investigating eco-physiological indicators of microbial biomass and microbial diversity with culture-dependent and independent techniques. Moreover, SNPs bioavailability and uptake were assessed. Soil samples were spiked with SNPs at two different concentrations (10 and 100 μg g(-1)dw) and incubated with the relative controls for 30, 60 and 90 days. The overall parameters showed a significant influence of the SNPs on the soil microbial community, revealing a marked shift after 60 days of incubation.

Effects of Cd- and Zn-enriched sewage sludge on soil bacterial and fungal communities

The effects of sewage sludge selectively enriched with Cd and Zn, both singly and in combination, on the bacterial, fungal, Alphaproteobacteria and Actinobacteria communities of a soil under arable or grassland management were studied with a PCR-DGGE approach. The effects of Cd and Zn were evaluated after a short time (7 d) when the Cd and Zn solubility were low and the C availability was high, and again after 180 d when the labile sludge C was mineralized and the effects of heavy metals predominated. In the arable soil all treatments induced significant short-term changes in the studied microbial groups, and long-term changes were observed in Actinobacteria and fungal communities. In the grassland soil, all treatments induced significant short-term changes in the studied microbial groups except for Alphaproteobacteria and fungi, and long-term effects on the actinobacteria and fungal communities. It was concluded that incorporation of Cd- and Zn-rich sludge into soils may have both short- and long-term effects on various bacterial phylogenetic groups whereas the metals may be better tolerated by the dominant soil fungi. In this study the impact was greater in arable than in grassland soil.

Microbial biomass, respiration and enzyme activities after in situ aided phytostabilization of a Pb- and Cu-contaminated soil

We conducted a pilot-scale experiment to study the effects of an aided phytostabilisation on soil microbial and biological endpoints in an ore dust-contaminated soil. Soil was amended with alkaline fly ashes plus peat to reduce mobility of trace elements and vegetated with a proprietary grass/herb mixture. Results indicated that the proposed aided phytostabilization approach of Cu-Pb contaminaed soil significantly increased microbial biomass and respiration, reduced microbial stress and increased key soil enzyme activities. Further research is needed to unambiguously determine whether the soil biochemical endpoints that were studied responded more to decreased metal mobility or to general soil amelioration.

Functions of microbial communities and their importance to soil

Abstract

Soil is a peculiar biological system with microbial life located in a small volume and distributed like an oasis in a desolated land, a large microbial biomass and huge microbial diversity, and the presence of important extracellular biological molecules, such as enzymes and nucleic acids, adsorbed by soil particles and protected against microbial degradation. The huge microbial diversity probably is at the basis of the broad metabolic activity, versatility and adaptation of soil to varying environmental conditions. It is still not possible to assess the composition and functions of microbial communities inhabiting soil in spite of the advances in identifying unculturable microorganisms and gene expression by molecular techniques. Gene expression of unknown microbial species from soil has allowed the discovery of novel bioproducts and novel metabolic processes, with important implications in various human activities. However, the identification of all microbial species inhabiting soil and their numbers and functions is not the most suitable approach for a better understanding of soil functionality. For example, a holistic approach based on the determination of biologically meaningful pools and fluxes is the best approach to quantify the dynamics of main nutrients in soil. Among the molecular techniques applied to soil, the stable isotope probes technique is the most suitable for holistic studies because it involves tracking of a stable isotope atom from a particular substrate into components of microbial cells that provide phylogenetic and functional information, such as lipid, proteins, DNA or RNA.