Microbial Community Level Physiological Profiles Research Articles

Compost and Beneficial Pseudomonas Populations Promote Enzyme Activity, Amino Acids and Polymers Utilization Patterns in Heavy Metal Contaminated Soils

PGPR-assisted phytoremediation is a biotechnology offering opportunities to improve the state of contaminated soil ecosystems. The present study has investigated the potential of six beneficial isolates tolerant to Cd, Pb, and Zn and identified through 16S rDNA sequential analysis as Bacillus cereus, Pseudomonas putida, and Pseudomonas fluorescens to stimulate spinach growth and soil microbial community development in heavy metal-contaminated soil with or without the addition of compost. We found improved plant growth in all treatments with compost, but especially applying consortiums of isolates. Microbial enzyme activities and basal soil respiration were significantly higher in the rhizosphere and in amended treatments than in non-rhizosphere and control. The microbial community-level physiological profiles in the rhizosphere studied with the Ecoplates of BiologTM system showed increased metabolic potential in treatments with compost and beneficial bacteria. Principal component analysis revealed domination of amino acids and polymers utilizing communities in compost and bacterial consortium amended soils, carbohydrates and amino acids in compost and single strains application, and the lowest representation of amines and amides and phenolic compounds utilizers. Thus, may conclude that the use of quality organic amendments together with beneficial soil bacterial populations is a suitable and promising approach for the phytostabilization of soils contaminated with heavy metals.

The dependent correlation between soil multifunctionality and bacterial community across different farmland soils.

Microorganisms play a critical role in soil biogeochemical cycles, but it is still debated whether they influence soil biogeochemical processes through community composition and diversity or not. This study aims to investigate variation in bacterial community structure across different soils and its correlation to soil multifunctionality. Soil samples were collected from five typical farmland zones along distinct climatic gradients in China. The high-throughput sequencing (Illumina MiSeq) of 16S rRNA genes was employed to analyze bacterial community composition in each soil sample. Multivariate analysis was used to determine the difference in soil properties, microbial community and functioning, and their interactions. Cluster and discrimination analysis indicated that bacterial community composition was similar in five tested soil samples, but bacterial richness combined with soil enzyme activities and potential nitrification rate (PNR) contributed most to the differentiations of soil samples. Mantel test analysis revealed that bacterial community composition and richness were more significantly shaped by soil nutrient conditions and edaphic variables than bacterial diversity. As for soil multifunctionality, soil microbial community level physiological profiles were little affected by abiotic and biotic factors, while soil enzymes and PNR were also significantly related to bacterial community composition and richness, in addition to soil N and P availability. Cumulatively, soil enzymes' activities and PNR were greatly dependent on bacterial community composition and richness not diversity, which in turn were greatly modified by soil N and P availability. Therefore, in the future it should be considered for the role of fertilization in the modification of bacterial community and the consequent control of nutrient cycling in soil.

Microbial Community-Level Physiological Profiles and Genetic Prokaryotic Structure of Burned Soils Under Mediterranean Sclerophyll Forests in Central Chile.

Forest fires alter soil microbial communities that are essential to support ecosystem recovery following land burning. These alterations have different responses according to soil abiotic pre- and post-fire conditions and fire severity, among others, and tend to decrease along vegetation recovery over time. Thus, understanding the effects of fires on microbial soil communities is critical to evaluate ecosystem resilience and restoration strategies in fire-prone ecosystems. We studied the state of community-level physiological profiles (CLPPs) and the prokaryotic community structure of rhizosphere and bulk soils from two fire-affected sclerophyll forests (one surveyed 17 months and the other 33 months after fire occurrence) in the Mediterranean climate zone of central Chile. Increases in catabolic activity (by average well color development of CLPPs), especially in the rhizosphere as compared with the bulk soil, were observed in the most recently affected site only. Legacy of land burning was still clearly shaping soil prokaryote community structure, as shown by quantitative PCR (qPCR) and Illumina MiSeq sequencing of the V4 region of the 16S rRNA gene, particularly in the most recent fire-affected site. The qPCR copy numbers and alpha diversity indexes (Shannon and Pielou’s evenness) of sequencing data decreased in burned soils at both locations. Beta diversity analyses showed dissimilarity of prokaryote communities at both study sites according to fire occurrence, and NO3– was the common variable explaining community changes for both of them. Acidobacteria and Rokubacteria phyla significantly decreased in burned soils at both locations, while Firmicutes and Actinobacteria increased. These findings provide a better understanding of the resilience of soil prokaryote communities and their physiological conditions in Mediterranean forests of central Chile following different time periods after fire, conditions that likely influence the ecological processes taking place during recovery of fire-affected ecosystems.

Short-Term Resilience of Soil Microbial Communities and Functions Following Severe Environmental Changes

Soil microorganisms are key drivers of soil biochemical processes, but the resilience of microbial communities and their metabolic activity after an extreme environmental change is still largely unknown. We studied structural (bacterial and fungal communities) and functional responses (soil respiration, adenosine triphosphate (ATP) content, hydrolase activities involved in the mineralization of organic C, N, P and S, and microbial community-level physiological profiles (CLPPs)) during the microbial recolonization of three heat-sterilized forest soils followed by cross- or self-reinoculation and incubation for 1, 7 and 30 days. Soil ATP content, biochemical activities and CLPP were annihilated by autoclaving, whereas most of the hydrolase activities were reduced to varying extents depending on the soil and enzyme activity considered. During the incubation period, the combination of self- and cross-reinoculation of different sterilized soils produced rapid dynamic changes in enzymatic activity as well as in microbial structure and catabolic activity. Physicochemical properties of the original soils exerted a major influence in shaping soil functional diversity, while reinoculation of sterilized soils promoted faster and greater changes in bacterial community structure than in fungal communities, varying with incubation period and soil type. Our results also confirmed the importance of microbial richness in determining soil resilience under severe disturbances. In particular, the new microbial communities detected in the treated soils revealed the occurrence of taxa which were not detected in the original soils. This result confirmed that rare microbial taxa rather than the dominant ones may be the major drivers of soil functionality and resilience.

Microbial activity and community level physiological profiles (CLPP) of soil under the cultivation of spring rape with the Roundup 360 SL herbicide

PurposeThe use of glyphosate in agriculture raises a lot of controversy because research concerning its impact on the soil provides contradictory information. However, despite these negative opinions, glyphosate is still used in agricultural practice. Therefore, for a more complete assessment, the authors carried out research using traditional microbiological methods and a modern method of metabolic profile analysis in glyphosate-treated soil.MethodsThe study was carried out on the soil witch was sown with six cultivars of rapeseed. Seven days before harvest, the plants were sprayed with the herbicide. The analyses consisted in determining the number of selected groups of microorganisms, biochemical and enzymatic activity, and differentiation of the catabolic potential of soil microbial communities.ResultsThe results showed significant changes in the analyzed parameters. Respiratory activity and ammonification processes were stimulated in the treatments with rapeseed cultivation treated with the herbicide. Changes in the enzymatic activity were generally positive. The EcoPlate assessment of microbial community catabolism showed that the highest activity was recorded in the soil sown with the cultivars Belinda, Tamarin, and Sw svinto. Concurrently, these soils were characterized by the highest correlations between rapeseed cultivar and metabolic activity.ConclusionCultivation of specific plant varieties that reduce the negative effect of herbicides used in agriculture may be one of the methods to prevent soil degradation. In our research, Belinda turned out to be a cultivar, under the cultivation of which an increase in the activity of microorganisms was recorded most frequently compared to soil not sown with rapeseed.

Microbial community-level physiological profiles: Considering whole data set and integrating dynamics of colour development

Abstract Community Level Physiological Profiles (CLPPs) have been used as ecological indicators from long ago as they determine physiologic and metabolic potential of microbial communities and indicate the capability to adapt their metabolism to anthropogenic stressors or to changes in environmental conditions. Also, these profiles are proxies for functional diversity or functional traits of a microbial community, usually linked to the ecosystem functioning. However, statistical data analysis of CLPPs has turned out to be the main handicap in these studies. Specifically, the interference of inoculum density, the need to choose an optimal incubation time and the different profiles obtained depending on the incubation time-point limits its usefulness. To this aim, we have developed a new approach for CLPP data analysis that considers the whole data set and dynamics of colour development along the incubation period. This approach is based on compositional data (CoDa) transformation, which reflects relative rather than absolute information, followed by repeated measures multivariate analysis of variance and data representation in a canonical variates plot. The approach has been tested by using CLPPs from real fluvial biofilm samples affected by seasonality, flow stress and different sediment depth conditions, and it has been compared to the most classic applied approaches until today (incubation fixed point or curve integration, followed by a Principal Components Analysis). Our results highlight that the proposed approach (i) makes ecological interpretation of CLPPs more sensitive, (ii) clarifies differences between CLPPs even in situations of marked seasonality while classical approaches provided confounding results, (iii) produces ecologically meaningful results (i.e. the proposed approach showed significant differences in organic matter use capabilities among flow conditions and depth), and (iv) unifies the analysis methodology for CLPPs data. With this work we provide an R-script to be used in future studies.

Biological H2 and CO oxidation activities are sensitive to compositional change of soil microbial communities.

Trace gas uptake by microorganisms controls the oxidative capacity of the troposphere, but little is known about how this important function is affected by changes in soil microbial diversity. This article bridges that knowledge gap by examining the response of the microbial community-level physiological profiles (CLPPs), carbon dioxide (CO2) production, and molecular hydrogen (H2) and carbon monoxide (CO) oxidation activities to manipulation of microbial diversity in soil microcosms. Microbial diversity was manipulated by mixing nonsterile and sterile soil with and without the addition of antibiotics. Nonsterile soil without antibiotics was used as a reference. Species composition changed significantly in soil microcosms as a result of dilution and antibiotic treatments, but there was no difference in species richness, according to PCR amplicon sequencing of the bacterial 16S rRNA gene. The CLPP was 15% higher in all dilution and antibiotic treatments than in reference microcosms, but the dilution treatment had no effect on CO2 production. Soil microcosms with dilution treatments had 58%-98% less H2 oxidation and 54%-99% lower CO oxidation, relative to reference microcosms, but did not differ among the antibiotic treatments. These results indicate that H2 and CO oxidation activities respond to compositional changes of microbial community in soil.

Study on Carbon Source Screening Technology for Prevention and Control of Banana Fusarium Wilt

With the spread of banana Fusarium wilt and the aggravation of the damage, it has become the biggest threat to the banana industry. Many studies have shown that bio-organic fertilizer plays an important role in the prevention and control of banana wilt, but most studies focused on biocontrol bacterium screening, not screening carbon sources that could prevent banana wilt, which lead to organic fertilizer fertilization without better effect. So that, a pot culture experiment (I) with inoculating Fusarium oxysporum f. sp. Cubense (FOC) on bananas was carried out to screen the carbon sources, and d-malic acid (CS2) to prevent and control banana wilt had been screened out by Biolog technology and Principal Component Analysis of microbial community level physiological profiling. To verify application effects of CS2, another banana pot experiment (II) with FOC inoculation had been done. The results showed that: (1) CS2 can effectively improve the activity of soil microorganisms. (2) CS2 can significantly reduce FOC population in soil, and the FOC population treated with CS2 was respectively lower than that treated with control carbon source (CS1) and without carbon source (CK1) 48% and 59%. (3) The banana wilt infection rate and disease index of CS2 treatment were significantly smaller than those of CS1 and CK1. (4) CS2 can promote the growth and biomass accumulation of bananas in pathogenic soil. In conclusion, the screening technology studied here can be applied to screen out the carbon sources for prevention of banana Fusarium wilt, which has great significance to the improvement of prevention effect of biological organic fertilizers to banana wilt.

Novel soil quality indicators for the evaluation of agricultural management practices: a biological perspective

Developments in soil biology and in methods to characterize soil organic carbon can potentially deliver novel soil quality indicators that can help identify management practices able to sustain soil productivity and environmental resilience. This work aimed at synthesizing results regarding the suitability of a range of soil biological and biochemical properties as novel soil quality indicators for agricultural management. The soil properties, selected through a published literature review, comprised different labile organic carbon fractions [hydrophilic dissolved organic carbon, dissolved organic carbon, permanganate oxidizable carbon (POXC), hot water extractable carbon and particulate organic matter carbon], soil disease suppressiveness measured using a <i>Pythium</i>-<i>Lepidium</i> bioassay, nematode communities characterized by amplicon sequencing and qPCR, and microbial community level physiological profiling measured with MicroResp^TM. Prior studies tested the sensitivity of each of the novel indicators to tillage and organic matter addition in ten European long-term field experiments (LTEs) and assessed their relationships with pre-existing soil quality indicators of soil functioning. Here, the results of these previous studies are brought together and interpreted relative to each other and to the broader body of literature on soil quality assessment. Reduced tillage increased carbon availability, disease suppressiveness, nematode richness and diversity, the stability and maturity of the food web, and microbial activity and functional diversity. Organic matter addition played a weaker role in enhancing soil quality, possibly due to the range of composition of the organic matter inputs used in the LTEs. POXC was the indicator that discriminated best between soil management practices, followed by nematode indices based on functional characteristics. Structural equation modeling shows that POXC has a central role in nutrient retention/supply, carbon sequestration, biodiversity conservation, erosion control and disease regulation/suppression. The novel indicators proposed here have great potential to improve existing soil quality assessment schemes. Their feasibility of application is discussed and needs for future research are outlined.

Bioremediation of engine-oil contaminated soil using local residual organic matter.

Soil remediation industries continue to seek technologies to speed-up treatment and reduce operating costs. Some processes are energy intensive and, in some cases, transport can be the main source of carbon emissions. Residual fertilizing materials (RFM), such as organic residues, have the potential to be beneficial bioremediation agents. Following a circular economy framework, we investigated the feasibility of sourcing RFMs locally to reduce transport and assess possible bioremediation efficiency gains. RFMs were recruited within 100 km of the treatment site: ramial chipped wood (RCW), horse manure (MANR) and brewer spent grain (BSG). They were added to the land treatment unit’s baseline fertilizer treatment (FERT, “F”) to measure if they improved the remediation efficiency of an engine oil-contaminated soil (7,500 ± 100 mg kg−1). Results indicate that MANR-F was the only amendment more effective than FERT for petroleum hydrocarbons (PHC) reduction, while emitting the least CO2 overall. RCW-F was equivalent to FERT but retained more moisture. Although BSG contributed the most nitrogen to the soil, BSG-F retained excessive moisture, emitted more volatile organic compounds, contained less soil O2, and was less effective than the baseline treatment. Significantly more of the C16–C22 fraction was removed (63% ± 22%) than all other fractions (C22–C28, C28–C34, C34–C40), which were equally removed. Microbial community-level physiological profiling was conducted with Biolog Ecoplates™, and catabolic diversity differed between treatments (utilization rates of 31 carbon sources). MANR-F has the potential to increase PHC-remediation speed and efficiency compared to inorganic fertilizer alone. Other RFM promote moisture retention and diverse microbial catabolic activity. A variety of RFM are present across the globe and some can offer low-cost amendments to boost remediation efficiency, while reducing treatment time compared to traditional fertilizer-only methods.

A Statistics and Analyses System of Microbial Community Level Physiological Profiles (CLPP) Based on Excel

Microbial community level physiological profiles (CLPP) assessed using Biolog MicroPlates has effectively demonstrated the metabolic activities of multiple microbes. Due to a large volume of data, and complicated calculation process, the conventional low efficiency calculations delay the study. To empower researchers to quickly tabulate, compute, analyze and present data, we introduced A Biolog EcoPlate data statistics and analyses system (A-BEP-DSAS). It is implemented with Biolog EcoPlate data tested by an ELISA microplate reader (Molecular Devices Versamax). The data input-output process and visual calculation flow are performed using Excel table linked with built-in VBA programming language. We tested A-BEP-DSAS by data from a soil sample, and rapidly and accurately obtained the average well color development (AWCD) data, carbon source utilization, six common diversity indices and other calculation results. A-BEP-DSAS is an automated program based on Microsoft Excel VBA, with the advantages of easy operation, rapid analysis, process visualization, and also allows the user to choose the data source and optimum time for analysis.

Microbial Community Level Physiological Profiles of Active Mud Volcano Soils in Andaman and Nicobar Islands

The aim of this work was to determine if any differences exist in the community-level physiological profiles (CLPP) in different regions of mud volcano. The microbial functional diversity in the four soils sampled in the vicinity of a mud volcano, Baratang, Andaman and Nicobar Islands, India, was determined using Biolog EcoPlates. Comparisons of the patterns of substrate use showed differences in the community composition, reflecting the heterogeneous distribution of microorganisms in this environment. The results showed statistically significant differences among different volcanic environments both by total colony-forming unit and by average well colour development. On the basis of similarity percentage analysis, it was found that i-erythritol was the most commonly used substrate, but substrates such as dl-glycerol phosphate (end mud volcano × point mud volcano), l-asparagine (end mud volcano × dried mud volcano) and ketobutyric acid (outside mud volcano × point mud volcano) were found in only one environment. The metabolic diversity varied depending on the environments compared, indicating specific utilization of compounds’ effect. Microbial response in terms of the overall metabolic activity in outside mud volcano was higher than in other inside mud volcano soils. To the best of our knowledge, this is the first attempt to use CLPP study in volcanic environments in the Andaman and Nicobar Islands.

Role of substrate supply on microbial carbon use efficiency and its role in interpreting soil microbial community-level physiological profiles (CLPP)

Carbon use efficiency (CUE) describes the relative partitioning of carbon (C) between anabolic and catabolic processes within the soil microbial community. Further, it represents a major factor regulating the amount of C cascading through the trophic levels of the soil food web. How CUE relates to C supply, however, remains poorly understood. The primary aim of this study was to determine how CUE varies across a range of spatial scales as a function of C substrate supply. Our secondary aim was to understand how variations in substrate CUE influences the interpretation of community level physiological profiles (CLPP). Using 16 different 14C-labelled substrates (including amino acids, sugars, organic acids and amino sugars) and soils collected at the field, regional and continental scale, we measured the rate of substrate uptake and mineralization from which we calculated CUE. Across all soils (n = 114) and substrates (n = 16), the average CUE for the microbial community was 0.568 ± 0.004 (range 0.492–0.794). While the partitioning of substrate-C within the biomass (immobilization/mineralization) over 72 h was highly conserved for some substrates (e.g. glucose), others showed a wide variability in CUE across the samples (e.g. valine). In the context of the CLPP methodology, we showed that individual sites could be statistically separated from each other, irrespective of whether the statistical analysis was based on microbial substrate uptake rate or mineralization rate. However, our results do suggest that caution is needed when ascribing observed CLPP differences to the importance of individual C pathways operating in soil due to the wide variation of CUE between substrates. In conclusion, we present new mechanistic evidence to support the paradigm that variation in ecosystem CUE may in part reflect differences in the types of C supplied to the microbial biomass.

Decoupled linkage between soil carbon and nitrogen mineralization among soil depths in a subtropical mixed forest

Deep soil stores a large amount of organic carbon (C) and nitrogen (N). However, little is known regarding the interactions between soil C and net N mineralization in deep soil, which complicates the prediction of ecosystem C and N dynamics. In this study, a 150-day laboratory soil incubation experiment was performed under 20 °C and 25 °C to investigate the influence of soil depth and warming on C and net N mineralization and their relationship. Soils were collected from a Hapludalfs profile in a subtropical forest with three depth intervals: 0–10 (topsoil), 10–30 (midsoil), and 30–60 cm (subsoil). Soil microbial community-level physiological profiling (CLPP) was conducted to investigate the role of the microbial community in C and N mineralization. The results demonstrated that both C and net N mineralization rates in subsoil were significantly lower than in topsoil. Compared to topsoil, subsoil had lower temperature sensitivity of C mineralization and relatively higher temperature sensitivity of net N mineralization. Cumulative soil C and net N mineralized were positively correlated in topsoil with the mineralized N per mineralized C showed as 0.19 and 0.31 at 20 °C and 25 °C, respectively. However, there was no significant correlation between cumulative soil C and net N mineralized in subsoil due to the low amount of net N mineralization. The lack of labile C source and degradable organic N were believed to limit the net N mineralization in subsoil. The microbial community in topsoil used relatively more easily decomposable carbohydrates and carboxylic acids, which favored C mineralization. In contrast, the microbial community in subsoil had relatively high utilization of amino acids (N-containing substrates), which indicated there was N limitation. This distinguished substrate utilization patterns of microbial communities could explain the observed C and N mineralization rates among the soil depths, and suggests that the microbial community played an important role in soil C and N mineralization. The decoupled relationships between soil C and net N mineralization in deep soil and their differentiated responses to warmer temperatures among soil depths indicated that deep soil should be considered separately from topsoil for ecosystem C and N cycling, especially for ecosystem C dynamic models.

Phytoremediation of strontium contaminated soil by Sorghum bicolor (L.) Moench and soil microbial community-level physiological profiles (CLPPs)

Phytoremediation of strontium contaminated soil by Sorghum bicolor (L.) Moench was investigated, and the soil microbial community-level physiological profiles (CLPPs) were examined. The growth and the stable strontium (88Sr) accumulations of the energy crop S. bicolor grown on the Sr-spiked soil at the level of 0, 50, 100, 200, and 400mg/kg soil were characterized through pot soil system after the entire growth period (140days). Correspondingly, the available content of strontium in soil extracted by Mehlich III extraction solution reached 42.0, 71.9, 151.8, and 242.2mg/kg, respectively. The Sr-polluted soil microbial community was assessed by a Biolog Eco-plate method. The results showed that the spiked Sr significantly increased the height and the stem biomass weight of the plant. Sr contents in roots, stems, and leaves of the sorghum increased linearly (R 2>0.95) with the elevation of the Sr-spiked level in soil. The average Sr concentration in roots, stems, and leaves reached 68.9, 61.3, and 132.6mg/kg dry weight (DW) under Sr-spiked 400mg/kg soil, respectively. Sr content in tissues decreased in the order of leaves > roots > stems. The bioconcentration factor (BCF; Sr contents in shoots to soil) values of S. bicolor in soil system was lower than 1 (0.21∼0.39) whether based on the spiked Sr level or on the available Sr level in soil. The transfer factor (TF; Sr contents in shoots to roots) values of S. bicolor in soil system usually is higher than 1 or near to 1 (0.92∼1.29). TF values increased while BCF values decreased as the soil Sr increased. The Biolog Eco-plate assay showed that Sr at the spiked level of 400mg/kg soil enhanced the soil microbial diversity and activity.

Microbial Community-Level Physiological Profiling as an Inquiry Laboratory Exercise

In this inquiry activity, community-level physiological profiling (CLPP) with EcoPlates is described to quantitatively depict the community of microorganisms situated in a natural environment. Students can develop their own hypotheses and carry out experimentation about the makeup of microbial communities using EcoPlates. There are many independent variables that can be assessed or changed to determine how environmental differences can play important roles in the types of microorganisms that are found in an environment.

Changes in the activity and abundance of the soil microbial community in response to the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP)

The application of organic and inorganic fertilizers to soil can result in increased gaseous emissions, such as NH3, N2O, CO2, and CH4, as well as nitrate leaching, contributing to climate warming and ground and surface water pollution, particularly in regions with hot climates, where high temperatures and high soil nitrification rates often occur. The use of nitrification inhibitors (NIs) has been shown to effectively decrease nitrogen (N) losses from the soil-plant system. Non-disruptive laboratory incubation experiments were conducted to assess the extent to which temperature (20 and 30 °C) and nutrient source (mineral and organic fertilizers) influence the rate of carbon (C)- and N-related microbial processes in soil in response to the NI 3,4-dimethylpyrazole phosphate (DMPP). Furthermore, short-term changes in the ability of microbes to degrade C substrates were evaluated in disruptive soil microcosms using microbial community-level physiological profiling and the abundance of the bacterial 16S rRNA gene as a measure of total bacterial population size. DMPP reduced net nitrification after 2 and 4 weeks of incubation at 30 and 20 °C by an average of 78.3 and 84.5 %, respectively, and with similar dynamics for mineral or organic fertilization. The addition of labile organic matter with cattle effluent led to a rapid increase in C mineralization that was significantly reduced by DMPP at both temperatures, whereas no changes could be detected after the addition of mineral fertilizer. The culturable heterotrophic microorganisms showed metabolic diversification in the oxidation of C sources, with organic fertilizer playing a major role in the substrate utilization patterns during the first week of incubation and the DMPP effects prevailing from day 14 until day 28. Furthermore, the copy number of the bacterial 16S rRNA gene was reduced by the application of DMPP and organic fertilizer after 28 days. Our results show the marked efficiency of DMPP as an NI at elevated temperatures of incubation and when associated with both mineral and organic fertilization, providing support for its use as a tool to mitigate N losses in Mediterranean ecosystems. However, we also observed impaired C respiration rates and bacterial abundances, as well as shifts in community-level physiological profiles in soil, possibly indicating a short-term effect of DMPP and organic fertilizers on non-target C-related processes and microorganisms.

Assessment of the effects of phytogenic nebkhas on soil nutrient accumulation and soil microbiological property improvement in semi-arid sandy land

Phytogenic nebkhas formed by shrubs, widely distributed in arid and semiarid ecosystems, commonly results in the patchiness of vegetation and strongly affect the spatial distribution of soil resources. In this study, we investigated the soil nutrient contents (organic matter, total N and P, and available N, P, and K), enzymatic activities (polyphenol oxidase, phosphomonoesterase, dehydrogenase, urease, and protease), and microbial community level physiological profiles for carbon source utilization in varying soil depths in different microsites within nabkhas, under the crown, and outside nabkhas of Caragana microphylla, Atraphaxis manshurica, and Salix gordejevii nebkhas in the western Horqin Sandy Land in Northeast China. Our main objectives were to determine whether “islands of fertility” developed both within and under the crown of the three nabkha types, to test whether the effects of islands of fertility differ among nebkha types, and to study the spatial heterogeneities of soil microbiological properties. Soil nutrients decreased with soil depth and with the distances from the center of each nebkha. The three nebkha types all created spatially heterogeneous patterns of soil nutrient within and around the nebkhas. Island of fertility effect varied among the nebkha types. C. microphylla nebkha had the highest enrichment ratios in soil organic matter and available N and P, whereas A. manshurica had the highest ratios in total N and P, and S. gordejevii had the highest ratio in available K. Phytogenic nebkhas also increased soil enzymatic activities and functional diversity for carbon source utilization of soil microflora. Enzyme activities among the microsites varied with enzyme type and shrub species. Phytogenic nebkhas can be considered major sources of soil nutrient and heterogeneity in microbiological property in the semi-arid ecosystem. Thus, more attentions to the management of phytogenic nebkhas should be considered in ecological restoration practices in semi-arid regions.

Soil Microbial Community-Level Physiological Profiling as Related to Carbon and Nitrogen Availability Under Different Land Uses

The goal of this work was to assess soil microbial respiration, determined by the assay of community-level physiological profiling in an oxygen-sensitive microplate (O2-CLPP), in response to endogenous C and several individual C substrates in the soils with different organic C contents (as a function of soil type and management practice). We also used the O2-CLPP to determine the respiratory response of these soils to endogenous C and amended C substrates with N addition. A respiratory quotient (RQ) was calculated based on the ratio of the response to endogenous soil C vs. each C-only substrate, and was related to total organic carbon (TOC). For assessing N availability for microbial activity, the effect of N supplementation on soil respiration, expressed as Nratio, was calculated based on the response of several substrates to N addition relative to the response without N. Soils clustered in 4 groups after a principal component analysis (PCA), based on TOC and their respiratory responses to substrates and endogenous C. These groups reflected differences among soils in their geographic origin, land use and C content. Calculated RQ values were significantly lower in natural forest soils than in managed soils for most C-only substrates. TOC was negatively correlated with RQ (r = −0.65), indicating that the soils with higher organic matter content increased respiratory efficiency. The N addition in the assay in the absence of C amendment (i.e., only endogenous soil C present) had no effect on microbial respiration in any soil, indicating that these soils were not intrinsically N-limited, but substrate-dependent variation in Nratio within soil groups was observed.

Soil microbial functional activity is governed by a combination of tree species composition and soil properties in temperate forests

Soil microbial community function is influenced, among other factors, by the chemical composition of C substrates, which in turn is dependent on the overlying tree species and the soil environmental conditions. The aim of this study was to examine how different dominant forest species and soil properties are related to soil microbial community level physiological profiles (CLPPs) in temperate forests. Forest floor properties and physico-chemical properties of the topsoil (0–30cm) and the subsoil (30–60cm) were studied in National Forest Inventory (NFI) plots differing in the dominant tree species (Quercus robur L., Fagus sylvatica L., Quercus ilex L. and Pinus radiata D. Don) but affected by similar climatic conditions. Soil microbial functional activity was assessed by the MicroResp analytical system. The only forest floor properties that differed significantly under different tree species were the concentrations of Ca, Mg and K. The forest floor of oak plots was characterized by higher concentrations of Mg and K, and the forest floor in holm oak plots by higher concentrations of Ca than in the other stands. Holm oak plots were also characterized by significantly higher concentrations of topsoil organic matter, nitrogen, phosphorus and potassium than beech, oak and pine, as well as a higher cation exchange capacity. Substrate C respiration was always higher for carboxylic acids than other substrates and the activity of soil microbial communities was higher under beech and holm oak than under oak and pine. The Mantel partial test and forward stepwise regression revealed that the soil microbial activity in the topsoil was mainly related to the topsoil N concentration. Most of the variation in CLPP in the subsoil was related to the concentration of Ca and pH in the subsoil. In conclusion, the soil microbial functional activity was related to both forest species and soil properties