Soil Metabolic Activity Research Articles

Effects of microplastics on the environmental behaviors of the herbicide atrazine in soil: Dissipation, adsorption, and bioconcentration

As an emerging contaminant in soil, the impact of microplastics (MPs) on the environmental behavior of other organic pollutants remains uncertain, potentially threatening the sustainability of agricultural production. In this study, the impact of two kinds of MPs on the environmental behaviors of herbicide atrazine in soil-plant system was investigated. The results showed that MPs significantly reduced the half-life 17.69 ∼ 21.86 days of atrazine in the soil, compared to the control group. Meanwhile, the introduction of MPs substantially increased atrazine adsorption. Additionally, MPs substantially enriched the diversity and functionality of soil microbiome, and the soil metabolic activity was stimulated. Regarding the crop growth, the accumulation of atrazine in maize were significantly decreased by approximately 48.4–78.5 % after exposure to MPs. In conclusion, this study reveals the impact of MPs on atrazine's environmental behaviors in soil and highlights their less effect on maize growth, providing valuable insights for managing MPs contamination in sustainable agriculture.

Elevated [CO2] enhances soil respiration and AMF abundance in a semiarid peanut agroecosystem

Rising atmospheric carbon dioxide [CO2] is a main climate change driver, and soil respiration is the most relevant contributor to ecosystem respiration. However, the soil microbiome and respiration responses of semiarid agroecosystems under elevated [CO2] (eCO2) conditions must be better understood. In particular, peanut agroecosystems host rhizobia and arbuscular mycorrhizal fungi (AMF) associations. Here, we sought to address the following questions: a) Does eCO2 conditions (650 µmol CO2 m−2 s−1, +250 µmol CO2 m−2 s−1, aCO2, control) alter soil chemical properties, soil microbial community size and composition, soil respiration, and β-Glucosidase activity? b) Are these responses influenced by transient water deficit periods? We conducted this study in a typical West Texas semiarid region (no well-watered treatment and drought was not an experimental factor) during two consecutive growing seasons (May-Oct). We induced the atmospheric CO2 enrichment using field-installed Canopy Evapotranspiration and Assimilation (CETA) systems. Our results showed no consistent significant changes in soil moisture, C: N ratio, total soil microbial EL-FAME abundance, or β-Glucosidase activity. However, we found that eCO2 increased soil temperature (+1 °C), AMF abundance (EL-FAME marker, +49%), and soil respiration (+82%). Our findings suggest that in future semiarid climates, peanut agroecosystems may experience: 1) increased soil metabolic activity as a result of increased autotrophic respiration; 2) increased AMF, which could further facilitate plant nutrient and water uptake; and 3) minimal change in the total size of the microbial community and C cycling enzyme activity during the growing season. In this manuscript, we demonstrated that soil respiration and temperature could be indicators of ecosystem productivity and climate feedback. Furthermore, soil organic carbon and AMF were good indicators of poor nutrient soil ecosystem transitional health across well-watered and water-deficit cycles. This study will increase our understanding of how these changes will affect soil ecology and climate feedback and will provide new insight into the peanut agroecosystem carbon source/sink functioning and productivity in future climates.

Bio-organic fertilizers improve Dendrocalamus farinosus growth by remolding the soil microbiome and metabolome.

Organic and microbial fertilizers have potential advantages over inorganic fertilizers in improving soil fertility and crop yield without harmful side-effects. However, the effects of these bio-organic fertilizers on the soil microbiome and metabolome remain largely unknown, especially in the context of bamboo cultivation. In this study, we cultivated Dendrocalamus farinosus (D. farinosus) plants under five different fertilization conditions: organic fertilizer (OF), Bacillus amyloliquefaciens bio-fertilizer (Ba), Bacillus mucilaginosus Krassilnikov bio-fertilizer (BmK), organic fertilizer plus Bacillus amyloliquefaciens bio-fertilizer (OFBa), and organic fertilizer plus Bacillus mucilaginosus Krassilnikov bio-fertilizer (OFBmK). We conducted 16S rRNA sequencing and liquid chromatography/mass spectrometry (LC-MS) to evaluate the soil bacterial composition and soil metabolic activity in the different treatment groups. The results demonstrate that all the fertilization conditions altered the soil bacterial community composition. Moreover, the combination of organic and microbial fertilizers (i.e., in the OFBa and OFBmK groups) significantly affected the relative abundance of soil bacterial species; the largest number of dominant microbial communities were found in the OFBa group, which were strongly correlated with each other. Additionally, non-targeted metabolomics revealed that the levels of soil lipids and lipid-like molecules, and organic acids and their derivatives, were greatly altered under all treatment conditions. The levels of galactitol, guanine, and deoxycytidine were also markedly decreased in the OFBa and OFBmK groups. Moreover, we constructed a regulatory network to delineated the relationships between bamboo phenotype, soil enzymatic activity, soil differential metabolites, and dominant microbial. The network revealed that bio-organic fertilizers promoted bamboo growth by modifying the soil microbiome and metabolome. Accordingly, we concluded that the use of organic fertilizers, microbial fertilizers, or their combination regulated bacterial composition and soil metabolic processes. These findings provide new insights into how D. farinosus-bacterial interactions are affected by different fertilization regiments, which are directly applicable to the agricultural cultivation of bamboo.

Application of Dairy Effluents to Pastures Affects Soil Nitrogen Dynamics and Microbial Activity

The use of farm dairy effluents (FDE) has become a promising alternative to increase pasture yield while reducing the environmental impact of waste accumulation into streams, but other environmental implications should be considered. The present study aimed to assess the effect of application of either raw FDE or lagoon-stored FDE compared to dissolved urea or a non-amended control on N2O emission, soil N dynamics, functional microbial activity, and the yield and N-use efficiency of a fescue pasture. The normalized N application rate of 200 kg N ha−1 was divided into four seasonal events in a greenhouse experiment. Similar fescue forage production with FDE or urea positioned FDE application to soil as an alternative disposal. The repeated application of raw effluent delivered more organic C to the soil which induced an increase in enzyme activities, a shift in the catabolic activity of the soil microbial community, and greater N mineralization potential. On the other hand, urea addition decreased the functional activity of the soil microbial community. However, N2O emissions were greater for the raw effluent, so lagoon-stored effluent is an alternative to manage FDE under these conditions, avoiding urea addition and enhancing soil metabolic activity.

Effects of Reductive Soil Disinfestation Combined with Liquid-Readily Decomposable Compounds and Solid Plant Residues on the Bacterial Community and Functional Composition.

Reductive soil disinfestation (RSD) incorporated with sole plant residues or liquid-readily decomposable compounds is an effective management strategy to improve soil health. However, the synthetic effects of RSD incorporated with liquid-readily decomposable compounds and solid plant residues on soil ecosystem services remain unclear. Field experiments were carried out to investigate the effects of untreated soil (CK), RSD incorporated with sawdust (SA), molasses (MO), and their combinations (SA + MO) on the bacterial community and functional composition. The results showed that RSD treatments significantly altered soil bacterial community structure compared to CK treatment. The bacterial community structure and composition in MO and SA + MO treatments were clustered compared to SA treatment. This was mainly attributed to the readily decomposable carbon sources in molasses having a stronger driving force to reshape the soil microbial community during the RSD process. Furthermore, the functional compositions, such as the disinfestation efficiency of F. oxysporum (96.4 - 99.1%), abundances of nitrogen functional genes, soil metabolic activity, and functional diversity, were significantly increased in all of the RSD treatments. The highest disinfestation efficiency and abundances of denitrification (nirS and nrfA) and nitrogen fixation (nifH) genes were observed in SA + MO treatment. Specifically, SA + MO treatment enriched more abundant beneficial genera, e.g., Oxobacter, Paenibacillus, Cohnella, Rummeliibacillus, and Streptomyces, which were significantly and positively linked to disinfestation efficiency, soil metabolic activity, and denitrification processes. Our results indicated that combining RSD practices with liquid-readily decomposable compounds and solid plant residues could effectively improve soil microbial community and functional composition.

Macrotyloma axillare ‘Java’ and Crotalaria spp. combined with biocontrol agents for the management of Meloidogyne javanica in soybean

AbstractThis study aimed to investigate the effects of crop rotation with Macrotyloma axillare ‘Java’, Crotalaria spectabilis and Crotalaria ochroleuca combined with green manure application or biological treatment, on the control of Meloidogyne javanica in soybean. An initial greenhouse study was conducted in a 4 × 2 factorial design, with four rotation crops (M. axillare ‘Java’, C. spectabilis, C. ochroleuca and soybean) in the presence and absence of green manure. A second greenhouse study was carried out using a 4 × 5 factorial design, with four rotation crops and five biocontrol treatments (Pochonia chlamydosporia, Purpureocillium lilacinum + Trichoderma harzianum, Bacillus methylotrophicus, Bacillus subtilis + Bacillus licheniformis and untreated control). Both experiments consisted of two independent trials (Trials 1 and 2) conducted at different times of the year. The experimental field soil was infested by growing soybean infected with M. javanica for 50 days prior to the assays. Then, seeds of rotation crops were sown and biocontrols applied. Rotation crops were removed 70 days after sowing, and soybean seeds were sown immediately afterwards. Total nematodes, nematode per gram of root and soil biological activity were assessed 60 days after soybean sowing. In the first study, all rotation systems and green manure treatments reduced M. javanica population. In the second study, all biological treatments were effective, except B. methylotrophicus and M. axillare ‘Java’ combined with P. chlamydosporia in Trial 1 and C. spectabilis combined with P. lilacinum +T. harzianum in Trial 2. Macrotyloma axillare ‘Java’ combined with B. methylotrophicus and C. spectabilis combined with B. subtilis +B. licheniformis resulted in higher soil metabolic activity. The association of biological control agents with crop rotation generally did not present additive effects in the reduction in M. javanica populations, except for one combination of M. axillare ‘Java’ with B. subtilis +B. lichneniformis.

Microbial community responses to multiple soil disinfestation change drivers

Soil continuous cropping obstacles lead to yield and economic losses in agriculture. Reductive soil disinfestation (RSD) is an effective technology for alleviating it. However, the key factors influencing microbial community composition and how do they promote functional transformation of core microbes under RSD practice remain poorly understood. Hence, a short-term field experiment was performed integrating real-time polymerase chain reaction, average well color development (AWCD), and MiSeq pyrosequencing to investigate relationships between environmental factors and microorganisms in five different disinfestation treatments, i.e., untreated monoculture soil (CK), soil with high temperature heating (HT), soil with dazomet (DZ), RSD with sugarcane bagasse (SB), or with bean dregs (BD). The results showed that compared to non-RSD treatments, both RSD treatments significantly increased soil microbial abundance and soil available K and organic matter (OM). Further analysis found that available K and OM were the key factors inducing microbial community change. Additionally, relative to non-RSD treatments, the relative abundances of phyla Proteobacteria, Acidobacteria, Rokubacteria, and Ascomycota were higher, whereas those of Actinobacteria, Gemmatimonadetes, and Basidiomycota were lower in RSD treatments. Changes in microbial diversity and abundance led to variation of soil microbial community functions. AWCD and community function prediction showed that, in contrast with non-RSD treatments, soil metabolism activity significantly increased, bacterial community functions including terpenoids and polyketides metabolism, signal transduction and cell motility increased, and the number of saprotroph fungi increased under RSD treatments. Overall, RSD incorporated with sugarcane bagasse or bean dregs efficiently improved soil fertility, and considerably increased soil microbial activity and function, which may benefit future sustainable agriculture production. Key points • Reductive soil disinfestation can alleviate continuous cropping obstacles by improving soil fertility. • Organic matter and available potassium as the key factors affected microbial community reconstruction and function. • Reductive soil disinfestation can improve soil metabolic activity and functional diversity by altering microorganism community.

What Physical Aspects Influence Biochemical Activity in Soil in a Natural Landscape?

The objective of this paper was to evaluate the effect of depth, seasonality and phytophysiognomies on the biochemical activity of soils in native Cerrado biome. Additionally, we listed which chemical parameters influence the activity of the microbiota and enzymatic activity in these environments. We selected eight sampling areas of Cerradão (Forest) and four areas of Cerrado (shrub land) and evaluated the chemical characteristics and biochemical activity. The depth, sampling site and seasonality directly affected soil metabolic activity. Microbial biomass carbon was influenced by interaction between soil depth and sampling site and the enzyme activity tends to be higher in the superficial layer of the soil. The analysis of redundancy showed strong influence of environmental variables (phosphorus and CTC) on the biological activity of the soil. Thus, the metabolic activity of microorganisms is highly influenced by intrinsic soil characteristics of each sampling site.

Effects of different straw biochars on soil organic carbon, nitrogen, available phosphorus, and enzyme activity in paddy soil

Biochar is widely used as a soil amendment. Enzyme activity is an important factor that reflects soil metabolic activity, and is involved in biochemical processes such as organic matter decomposition and nutrient cycling in soils. However, the effects of biochar prepared for different straw materials on soil enzyme activity and soil nutrients are rarely studied. Through pot experiments, the effects of different straw (wheat, rice, maize) biochars (obtained by pyrolysis at 500 °C) on soil organic carbon, nitrogen, available phosphorus, and enzyme activity were studied in paddy soil. The results showed that the addition of biochar increased the soil organic carbon content, which gradually decreased with the extension of the rice growth period. The soil ammonium nitrogen content gradually decreased as the rice growth period continued; however, the soil nitrate nitrogen content first decreased and then increased over the rice growth period. Soil invertase, phosphatase, and urease activity first increased and then decreased, and the enzyme activity was the highest at the heading stage of rice. At this time, there were also significant correlations between enzyme activity and carbon, nitrogen, and phosphorus levels, except in the case of soil urease activity. The geometric mean of the investigated enzyme activities was the highest after amendment with rice straw biochar. These results indicate that the response of enzyme activity to biochar depends on the biochar feedstock and the rice growth stage.

Differential responses of soil bacterial community and functional diversity to reductive soil disinfestation and chemical soil disinfestation

Reductive soil disinfestation (RSD) and chemical soil disinfestation (CSD) are two common agricultural strategies for the elimination of soil-borne pathogens. However, the differences in soil bacterial microbiome and its associated functional characteristics between CSD and RSD are poorly understood. In this study, five soil treatments, un-treated control (CK), CSD with 0.5 t ha−1 dazomet (DZ), RSD with 10 t ha−1 ethanol (ET), 15 t ha−1 sugarcane bagasse (SB), and 15 t ha−1 bean dregs (BD), were compared. We evaluated their effects on microbial metabolic activity, functional diversity, nitrogen-related genes abundance, and bacterial community structure using Biolog analysis, real-time PCR, and high-throughput sequencing. RSD-related treatments improved soil metabolic activity, functional diversity, and the abundance of denitrifying genes to a greater extent than the DZ treatment. Carbon source utilization preference and bacterial community structure were strikingly altered by CSD and RSD practices. Bacterial richness, diversity, and evenness were notably lowered in the SB- and BD-treated soils compared with the CK and DZ-treated soils. Moreover, compared with the DZ- and ET-treated soils, the SB- and BD-treated soils harbored distinct unique and core microbiomes that were comprised of more abundant and diverse potentially disease-suppressive and organic-decomposable agents. Collectively, these results suggest that RSD practices incorporated with organic residues could considerably restore soil functional activity and diversity, and act as a potential agricultural practice for the development of disease-suppressive soils.

Effect of waterlogging on soil biochemical properties and organic matter quality in different salt marsh systems

This study investigated the effects of hydroperiod on soil organic matter quality in three different salt marshes in the Baiona lagoon (N Italy) representing terrestrial, intertidal and subaqueous ecosystems in the area. The study specifically aimed to gain some insight into how soil waterlogging (hydroperiod) affects the chemical and biological properties of soils as well as the quality and structure of the soil organic matter (SOM). Total contents of selected nutrients, total organic carbon and carbon stable isotope (δ13C) were measured in all soil profiles. The results of these analyses enabled us to define the different origin of the SOM by discriminating between terrestrial and aquatic SOM sources. The findings also show that accumulation of nutrients and SOM is significantly magnified in intertidal systems, in which pedoturbation effects induced by water movements are particularly strong. In addition, DRIFT spectra of humic acids revealed the changes in the main functional groups in relation to increased waterlogging, highlighting the lower aromaticity and complexity in subaqueous soils (SASs), which is possibly due to the effect of the soil water saturation on the chemical and biological SOM transformation processes. Microbial biomass carbon (MBC), microbial quotient (Qmic) and the activities of some soil enzymes were measured to estimate soil metabolic activity in the systems and to evaluate how the microbial pool contributes to transforming the SOM. In all systems, the enzymatic activities were generally higher in subsurface horizons than in the surface horizon. This unexpected behaviour can be explained by the combined effect of water movement, erosion processes and preservation of SOM under anaerobic conditions. This study represents an attempt to investigate and understand the ongoing degradation processes in salt marsh ecosystems. The findings emphasize the strong influence of water flow and erosional processes associated with soil waterlogging on chemical and biological reactions in intertidal and subaqueous systems.

Improvement of mining soil properties through the use of a new bio-conditioner prototype: a greenhouse trial

The effect of a prototype of humic bio-conditioner (H-BC) was assessed on the development of edaphic properties and the growth of maize plants in an edaphic material used as topsoil in the rehabilitation of soils in a coal mine in Colombia. The trial was carried out in a greenhouse, using pots with edaphic material treated with the addition of doses equivalent to 0 (control), 1, 2, and 4 Mg.ha−1 of H-BC; maize seeds were sown and followed up on for 60 days. Plant growth and soil biological, chemical, and physical variables were registered. The 4-Mg.ha−1 treatment maintained a significantly higher enzymatic activity than the control on day 60. The respiration of the soil treated with H-BC increased significantly, with the 4-Mg.ha−1 treatment standing out. The 2-Mg.ha−1 treatment induced the most noticeable changes in soil metabolic activity profiles. Increases in root and leaf development were observed in the treatment with 4 Mg.ha−1; apparently, this dose improved the absorption of Ca, K, and S by plants; the physical and soil aggregation indices increased significantly with 4 Mg.ha−1. The results indicate that H-BC can be an alternative as an enhancer of the edaphic material used in soil rehabilitation processes.

Present Situation and Evaluation of Contaminated Soil Disposal Technique

In recent years, because of the abuse of pesticides and fertilizers and the random discharge of sewage, the soil pollution is becoming more and more serious. At present, China’s soil environment is grim. The treatment of contaminated soil is the focus of current research in agriculture, environment and ecology. Because of the different types of soil pollution and soil properties, and the complex process of contaminated soil, many factors need to be considered. Common soil remediation techniques include: Chemical remediation, bioremediation technology. The bioremediation technologies include: animal remediation technology, phytoremediation technology and microbial remediation technology. Animal remediation technology is the use of lower animals in the soil metabolic activity degradation of organic pollutants in soil conversion. Phytoremediation technology refers to the absorption, enrichment, degradation, transformation of soil contaminants, to achieve the purpose of soil control. At present, phytoremediation technology has been widely used, which can effectively control heavy metal contaminated soil. Microbial remediation technology is the use of soil microbial metabolic activity of the soil in the degradation of pollutants into non-toxic substances.

Present Situation and Evaluation of Contaminated Soil Disposal Technique

In recent years, because of the abuse of pesticides and fertilizers and the random discharge of sewage, the soil pollution is becoming more and more serious. At present, China’s soil environment is grim. The treatment of contaminated soil is the focus of current research in agriculture, environment and ecology. Because of the different types of soil pollution and soil properties, and the complex process of contaminated soil, many factors need to be considered. Common soil remediation techniques include: Chemical remediation, bioremediation technology. The bioremediation technologies include: animal remediation technology, phytoremediation technology and microbial remediation technology. Animal remediation technology is the use of lower animals in the soil metabolic activity degradation of organic pollutants in soil conversion. Phytoremediation technology refers to the absorption, enrichment, degradation, transformation of soil contaminants, to achieve the purpose of soil control. At present, phytoremediation technology has been widely used, which can effectively control heavy metal contaminated soil. Microbial remediation technology is the use of soil microbial metabolic activity of the soil in the degradation of pollutants into non-toxic substances.

Microbial rRNA Synthesis and Growth Compared through Quantitative Stable Isotope Probing with H218O.

Growing bacteria have a high concentration of ribosomes to ensure sufficient protein synthesis, which is necessary for genome replication and cellular division. To elucidate whether metabolic activity of soil microorganisms is coupled with growth, we investigated the relationship between rRNA and DNA synthesis in a soil bacterial community using quantitative stable isotope probing (qSIP) with H218O. Most soil bacterial taxa were metabolically active and grew, and there was no significant difference between the isotopic composition of DNA and RNA extracted from soil incubated with H218O. The positive correlation between 18O content of DNA and rRNA of taxa, with a slope statistically indistinguishable from 1 (slope = 0.96; 95% confidence interval [CI], 0.90 to 1.02), indicated that few taxa made new rRNA without synthesizing new DNA. There was no correlation between rRNA-to-DNA ratios obtained from sequencing libraries and the atom percent excess (APE) 18O values of DNA or rRNA, suggesting that the ratio of rRNA to DNA is a poor indicator of microbial growth or rRNA synthesis. Our results support the notion that metabolic activity is strongly coupled to cellular division and suggest that nondividing taxa do not dominate soil metabolic activity.IMPORTANCE Using quantitative stable isotope probing of microbial RNA and DNA with H218O, we show that most soil taxa are metabolically active and grow because their nucleic acids are significantly labeled with 18O. A majority of the populations that make new rRNA also grow, which argues against the common paradigm that most soil taxa are dormant. Additionally, our results indicate that relative sequence abundance-based RNA-to-DNA ratios, which are frequently used for identifying active microbial populations in the environment, underestimate the number of metabolically active taxa within soil microbial communities.

Diversifying crop rotation increased metabolic soil diversity and activity of the microbial community

Agricultural intensification has increased food production by reducing crop diversity and increasing fertilization and crop protection. Unfortunately, intensification has also reduced soil ecosystem services. Diversifying crop rotations could be a feasible alternative to promote positive feedbacks between soil biota and soil properties. Here, we investigated the impact of diversifying crop rotations on functional composition and diversity of the heterotrophic soil bacterial communities. We studied three frequent rotations with a total number of crops ranging from two to four. Before the experiment, all plots were cultivated with soybean. In the first experimental year, the crop sequences were (1) fallow/soybean, (2) barley/soybean, and (3) field pea/maize. In the second year, all plots were subjected to a wheat/soybean double crop. The experiment was replicated in three locations of the Rolling Pampa (Argentina). Soil and plant sampling took place immediately after the soybean harvest, in the second year. The most diverse rotation (field pea/maize, wheat/soybean) showed the highest standing biomass and litter and the most metabolically diverse and active soil microbial community (P ≤ 0.05). In turn, metabolic diversity was positively associated with plant and litter biomass (r2 = 0.7) and with soil pH (r2 = 0.72). Our results revealed that crop rotation affects soil metabolic bacterial diversity and activity (P ≤ 0.05). The most diverse rotation (four different crops) had also the most diverse and active soil microbial biota, concomitantly with a higher plant biomass production and soil pH. Because soil microbial activity and metabolic diversity detected in specific rotations potentially contribute to soil aggregate formation and other soil properties intimately related with nutrient cycling and plant production, the negative effect of agricultural intensification could be attenuated by designing specific and more diverse crop rotations.

Soil metabolic activity profiles of the organic and conventional land use at Martonvásár

These days, increasing attention has been paid to understand the relationship between different farming systems and soil microbiological processes supporting sustainable land use. Soil microbiota have been considered as a priority component in organic land managements and sustaining soil health in long term. This statement should be supported by appropriately selected indicators - physiological properties or more precisely the metabolic activity profile of the soil microbes. A recently developed method, MicroRespTM gives a promising characterization of the catabolic activity pattern of the soil microbial communities. The goal of this study was to compare the catabolic profile of soil microbial communities of organic and conventional land management in a long-term experiment at Martonvásár (Hungary) from two consecutive years by two samplings (autumn and spring). MicroRespTM with 22 different substrates were used to characterize the catabolic activity patterns of these soils. Multivariate statistical analysis revealed a significant difference between the catabolic activity profiles of the soil microbial communities of the two management systems. Considering the soil chemical parameters, the AL-P2O5-K2O, NO3--N were responsible for the divergence of the two farming systems according to the principal component analysis (PCA). The biotic (crop) and abiotic (EC, humus content, pH) parameters could affect not only the rate of soil respiration but the catabolic activity profiles as well. Organic farming increased the catabolic activity of soil microbes.

Monitoring the changes in a bacterial community in petroleum-polluted soil bioaugmented with hydrocarbon-degrading strains

Bioaugmentation is a strategy used to enhance degradation of petroleum compounds in contaminated soils, however little is known about the interactions between introduced bacteria and autochthonous microflora. Therefore the objective of the study was to assess any changes in the structure and metabolic activity of the soil bacterial communities as a result of the introduction of Bacillus subtilis T′-1 or Pseudomonas sp. P-1, as well their consortium, into petroleum-contaminated soil. The bioaugmentation experiment was carried out under laboratory conditions using soil taken from an industrial area located around a refinery in Czechowice-Dziedzice. After the bioaugmentation process, a significant (P<0.05) decrease in the TPH content was reported in all inoculated soils. Inoculation of the soil with the bacterial consortium resulted in a three times greater removal of TPH compared to soils inoculated with single strains. It has been reported that all of the strains had an ability to survive in the environment during the experimental period. The introduction of bacterial strains led to increase in the number of 16S rRNA gene copies in soil on 1 and 7days of the experiment as well as alkB gene copies during 91days of the study compared to the non-treated soil. Analysis of the 16S rRNA and alkB genes-based DGGE fingerprints showed that introduced bacteria changed the genetic diversity of the total bacterial communities as well as the communities that have the genes involved in the degradation of hydrocarbons. Analysis of the PLFA profiles showed that the bacterial strains caused short-term changes in the amounts of fatty acids characteristic for Gram-positive and Gram-negative bacteria. The CLPPs indicated differences in soil metabolic activity between the inoculated and non-inoculated soils after the bioaugmentation process.

不同耕作方式对农田土壤微生物功能多样性的影响

为揭示耕作方式对华北农田土壤微生物群落功能多样性的影响，采用Biolog-Eco技术，研究了4种耕作处理(撂荒LF、翻耕FT、旋耕RT、免耕NT)土壤微生物群落功能多样性的变化。结果表明：1) 不同耕作方式下土壤微生物群落平均颜色变化率(Average well color development) AWCD值从高到低依次为LF > NT > RT > FT，LF、NT、RT的AWCD显著高于FT (P 0.05)。3) 主成分分析表明，RT与LF土壤微生物群落碳源利用类型相似。旋耕秸秆还田和撂荒有利于提高土壤微生物活性和土壤微生物群落功能多样性。 The aim was to study the influence of different tillage methods on functional diversity of soil mi-crobial community in the North China farming areas. Using the method of Biolog-Eco, a comparative study was made on the utilization level of single carbon source by the soil microbes of four tillage methods (abandoned LF, conventional FT, rotary RT, no-tillage NT). The results showed that: 1) the Average Well Color Development (AWCD) value of abandoned tillage, no-tillage, rotary tillage were significantly higher than conventional tillage (P 0.05); 3) principal component analysis indicated that the carbon source utilization of soil microbial community was similar among the rotary tillage and no-tillage treatment. In conclusion, rotary tillage with straw return and abandoned tillage were helpful to improve the soil metabolic activity of microorganism and the functional diversity of soil microbial communities.

Variation in soil organic matter accumulation and metabolic activity along an elevation gradient in the Santa Rosa Mountains of Southern California, USA

Variations in soil organic matter accumulation across an elevation can be used to explain the control of substrate supply and variability on soil metabolic activity. We investigated geographic changes in soil organic matter and metabolic rates along an elevation gradient (289–2,489 m) in the Santa Rosa Mountains, California, USA from subalpine and montane pine forests through chaparral to desert. From base (289 m) to summit (2,489 m), 24 sites were established for collecting soil samples under canopies and inter-canopy spaces, at 0–5 and 5–15 cm soil depths increments. Soil organic matter (SOM) content was determined using weight loss on ignition at 550°C and soil CO2 efflux (R) was measured at day 5 (R5) and day 20 (R20) of incubation. Changes in SOM content along the elevation gradient showed a significant relationship (P<0.05) but R5 and R20 were not related to either elevation or SOM content. However, the ratio of R and SOM (R5/SOM) showed a strong relationship across the mountains at both soil depths. R5/SOM, as an indicator of carbon use efficiency, may be applicable to other semi-arid transects at larger scale modeling of soil metabolic processes.