Comparison of soil microbial communities inhabiting vineyards and native sclerophyllous forests in central Chile

Natural ecosystems provide services to agriculture such as pest control, soil nutrients, and key microbial components. These services and others in turn provide essential elements that fuel biomass productivity. Responsible agricultural management and conservation of natural habitats can enhance these ecosystem services. Vineyards are currently driving land‐use changes in many Mediterranean ecosystems. These land‐use changes could have important effects on the supporting ecosystems services related to the soil properties and the microbial communities associated with forests and vineyard soils. Here, we explore soil bacterial and fungal communities present in sclerophyllous forests and organic vineyards from three different wine growing areas in central Chile. We employed terminal restriction fragment length polymorphisms (T‐RFLP) to describe the soil microbial communities inhabiting native forests and vineyards in central Chile. We found that the bacterial community changed between the sampled growing areas; however, the fungal community did not differ. At the local scale, our findings show that fungal communities differed between habitats because fungi species might be more sensitive to land‐use change compared to bacterial species, as bacterial communities did not change between forests and vineyards. We discuss these findings based on the sensitivity of microbial communities to soil properties and land‐use change. Finally, we focus our conclusions on the importance of naturally derived ecosystem services to vineyards.     

The Influence of Different Land Uses on the Structure of Archaeal Communities in Amazonian Anthrosols Based on 16S rRNA and amoA Genes

Soil from the Amazonian region is usually regarded as unsuitable for agriculture because of its low organic matter content and low pH; however, this region also contains extremely rich soil, the Terra Preta Anthrosol. A diverse archaeal community usually inhabits acidic soils, such as those found in the Amazon. Therefore, we hypothesized that this community should be sensitive to changes in the environment. Here, the archaeal community composition of Terra Preta and adjacent soil was examined in four different sites in the Brazilian Amazon under different anthropic activities. The canonical correspondence analysis of terminal restriction fragment length polymorphisms has shown that the archaeal community structure was mostly influenced by soil attributes that differentiate the Terra Preta from the adjacent soil (i.e., pH, sulfur, and organic matter). Archaeal 16S rRNA gene clone libraries indicated that the two most abundant genera in both soils were Candidatus nitrosphaera and Canditatus nitrosocaldus. An ammonia monoxygenase gene (amoA) clone library analysis indicated that, within each site, there was no significant difference between the clone libraries of Terra Preta and adjacent soils. However, these clone libraries indicated there were significant differences between sites. Quantitative PCR has shown that Terra Preta soils subjected to agriculture displayed a higher number of amoA gene copy numbers than in adjacent soils. On the other hand, soils that were not subjected to agriculture did not display significant differences on amoA gene copy numbers between Terra Preta and adjacent soils. Taken together, our findings indicate that the overall archaeal community structure in these Amazonian soils is determined by the soil type and the current land use.     

The Old and Young Amazon: Dung Beetle Biomass, Abundance, and Species Diversity

The Amazon Basin can be divided into two geomorphological regions based on the age of its soils: young (< 30 mya) and old (> 300 mya). We tested the effects of soil age on dung beetle communities by comparing biomass, abundance, and species between reserves in Ecuador on young soils and reserves in Brazil on old soils. Beetle biomass in the old Amazon was one-third that in the young Amazon, and beetle abundance in the old Amazon was one-fourth that in the young Amazon. Species richness, rarefied to equal sample sizes, was not significantly different between old and young soils. These data suggest young soils of the Amazon support a significantly greater biomass and abundance of dung beetles than old soils, but that species richness across the Basin is similar. As dung beetles are bio-indicators of mammals, our data support previous studies indicating a greater biomass of mammals on young versus old Amazon soils.     

Biogeographical patterns of soil molecular microbial biomass as influenced by soil characteristics and management

Aim The spatial organization of soil microbial communities on large scales and the identification of environmental factors structuring their distribution have been little investigated. The overall objective of this study was to determine the spatial patterning of microbial biomass in soils over a wide extent and to rank the environmental filters most influencing this distribution. Location French territory using the French Soil Quality Monitoring Network. This network covers the entire French territory and soils were sampled at 2150 sites along a systematic grid. Methods The soil DNA extracted from all these soils was expressed in terms of soil molecular microbial biomass and related to other soil and land‐use data over French territory. Results This study provides the first extensive map of microbial biomass and reveals the heterogeneous and spatially structured distribution of this biomass on the scale of France. The main factors driving biomass distribution are the physico‐chemical properties of the soil (texture, pH and total organic carbon) as well as land use. Soils from land used for intensive agriculture, especially monoculture and vineyards, exhibited the smallest biomass pools. Interestingly, factors known to influence the large‐scale distribution of macroorganisms, such as climatic factors, were not identified as important drivers for microbial communities. Main conclusions Microbial abundance is spatially structured and dependent on local filters such as soil characteristics and land use but is relatively independent of global filters such as climatic factors or the presence of natural barriers. Our study confirms that the biogeography of microorganisms differs fundamentally from the biogeography of ‘macroorganisms’ and that soil management can have significant large‐scale effects.     

Geochemical Assessment of Iron and Vanadium Relationships in Oxic Soil Environments

Geochemical assessment has become a cost-effective and highly accurate tool for estimating metal contamination, especially in those cases where the level of contamination is not considered severe. Difficulties frequently arise in attempting to discriminate between pristine metal concentrations and low-level environmental impacts. As an example, Vanadium contamination is frequently associated with coal and petroleum bi-products; however, air and water contamination pathways are also possible. The purpose of this investigation was to characterize the V and Fe concentration relationship among a wide variety of soil types and to formulate an estimate of the pristine V concentrations in these soils. If a linear relationship may be established between Fe and V, then geochemical analysis of impacted soils may discriminate between V as a natural background component and anthropogenic V. Forty-six moderately well-drained to well-drained soil profiles having cambic, argillic or calcic soil horizons were characterized for Fe and V using an aqua-regia digestion to determine if these soils exhibited a one-to-one correspondence between V and Fe. Such a correspondence was authenticated for the majority of these soils and may be used to discriminate between natural and anthropogenic V. The presence of argillic, calcic or fragipan horizons did not reduce the one-to-one correspondence between V and Fe, suggesting that these soil processes did not selectively partition either V or Fe. The method needs to be further evaluated for soils having anoxic soil conditions, lithologic discontinuities and other specific pedogenic processes.     

Influence of market orientation on food plant diversity of farms located on Amazonian Dark Earth in the region of Manaus, Amazonas, Brazil

Homegardens may serve as reservoirs of agro-biodiversity on highly fertile, anthropogenic Amazonian Dark Earth (ADE) soils of the Amazon basin. However, as these soils are used more intensively for market-oriented agriculture, we suspected a decrease in their agro-biodiversity. We present data obtained from surveys on 16 farms where ADE was present in the region of Manaus, Amazonas, Brazil. When farms were separated into two groups by market orientation, species richness on the farms was not significantly influenced by market orientation, but there was less dominance (i.e., more diversity) for homegardens in the low-market orientation group (P < 0.1). The proportion of native species was not affected by market orientation. Hence, while the most market-oriented farms retained high species richness, homegardens located on them contained higher proportions of commercially interesting species.     

Unravelling soil fungal communities from different Mediterranean land-use backgrounds

Background

Fungi strongly influence ecosystem structure and functioning, playing a key role in many ecological services as decomposers, plant mutualists and pathogens. The Mediterranean area is a biodiversity hotspot that is increasingly threatened by intense land use. Therefore, to achieve a balance between conservation and human development, a better understanding of the impact of land use on the underlying fungal communities is needed.

Methodology/Principal Findings

We used parallel pyrosequencing of the nuclear ribosomal ITS regions to characterize the fungal communities in five soils subjected to different anthropogenic impact in a typical Mediterranean landscape: a natural cork-oak forest, a pasture, a managed meadow, and two vineyards. Marked differences in the distribution of taxon assemblages among the different sites and communities were found. Data analyses consistently indicated a sharp distinction of the fungal community of the cork oak forest soil from those described in the other soils. Each soil showed features of the fungal assemblages retrieved which can be easily related to the above-ground settings: ectomycorrhizal phylotypes were numerous in natural sites covered by trees, but were nearly completely missing from the anthropogenic and grass-covered sites; similarly, coprophilous fungi were common in grazed sites.

Conclusions/Significance

Data suggest that investigation on the below-ground fungal community may provide useful elements on the above-ground features such as vegetation coverage and agronomic procedures, allowing to assess the cost of anthropogenic land use to hidden diversity in soil. Datasets provided in this study may contribute to future searches for fungal bio-indicators as biodiversity markers of a specific site or a land-use degree.     

Conversion of Amazon rainforest to agriculture alters community traits of methane‐cycling organisms

Land use change is one of the greatest environmental impacts worldwide, especially to tropical forests. The Amazon rainforest has been subject to particularly high rates of land use change, primarily to cattle pasture. A commonly observed response to cattle pasture establishment in the Amazon is the conversion of soil from a methane sink in rainforest, to a methane source in pasture. However, it is not known how the microorganisms that mediate methane flux are altered by land use change. Here, we use the deepest metagenomic sequencing of Amazonian soil to date to investigate differences in methane‐cycling microorganisms and their traits across rainforest and cattle pasture soils. We found that methane‐cycling microorganisms responded to land use change, with the strongest responses exhibited by methane‐consuming, rather than methane‐producing, microorganisms. These responses included a reduction in the relative abundance of methanotrophs and a significant decrease in the abundance of genes encoding particulate methane monooxygenase. We also observed compositional changes to methanotroph and methanogen communities as well as changes to methanotroph life history strategies. Our observations suggest that methane‐cycling microorganisms are vulnerable to land use change, and this vulnerability may underlie the response of methane flux to land use change in Amazon soils.     

Soil-Borne Bacterial Structure and Diversity Does Not Reflect Community Activity in Pampa Biome

The Pampa biome is considered one of the main hotspots of the world’s biodiversity and it is estimated that half of its original vegetation was removed and converted to agricultural land and tree plantations. Although an increasing amount of knowledge is being assembled regarding the response of soil bacterial communities to land use change, to the associated plant community and to soil properties, our understanding about how these interactions affect the microbial community from the Brazilian Pampa is still poor and incomplete. In this study, we hypothesized that the same soil type from the same geographic region but under distinct land use present dissimilar soil bacterial communities. To test this hypothesis, we assessed the soil bacterial communities from four land-uses within the same soil type by 454-pyrosequencing of 16S rRNA gene and by soil microbial activity analyzes. We found that the same soil type under different land uses harbor similar (but not equal) bacterial communities and the differences were controlled by many microbial taxa. No differences regarding diversity and richness between natural areas and areas under anthropogenic disturbance were detected. However, the measures of microbial activity did not converge with the 16S rRNA data supporting the idea that the coupling between functioning and composition of bacterial communities is not necessarily correlated.     

Comparisons of AM fungal spore communities with the same hosts but different soil chemistries over local and geographic scales

Arbuscular mycorrhizal (AM) fungi are ubiquitous and ecologically important microbes in grasslands. Both the host plant species and soil properties have been suggested as potentially important factors structuring AM fungal communities based on studies within local field sites. However, characterizations of the communities in relation to both host plant identity and soil properties in natural plant communities across both local and broader geographic scales are rare. We examined the AM fungal spore communities associated with the same C₄ grasses in two Eastern serpentine grasslands, where soils have elevated heavy metals, and two Iowa tallgrass prairie sites. We compared AM fungal spore communities among host plants within each site, looked for correlations between fungal communities and local soil properties, and then compared communities among sites. Spore communities did not vary with host plant species or correlate with local soil chemical properties at any site. They did not differ between the two serpentine sites or between the two prairie sites, despite geographic separation, but they did differ between serpentine and prairie. Soil characteristics are suggested as a driving force because spore communities were strongly correlated with soil properties when data from all four sites are considered, but climatic differences might also play a role.     

Molecular and Functional Assessment of Bacterial Community Convergence in Metal-Amended Soils

Species diversity and the structure of microbial communities in soils are thought to be a function of the cumulative selective pressures within the local environment. Shifts in microbial community structure, as a result of metal stress, may have lasting negative effects on soil ecosystem dynamics if critical microbial community functions are compromised. Three soils in the vicinity of a copper smelter, previously contaminated with background, low and high levels of aerially deposited metals, were amended with metal-salts to determine the potential for metal contamination to shape the structural and functional diversity of microbial communities in soils. We hypothesized that the microbial communities native to the three soils would initially be unique to each site, but would converge on a microbial community with similar structure and function, as a result of metal stress. Initially, the three different sites supported microbial communities with unique structural and functional diversity, and the nonimpacted site supported inherently higher levels of microbial activity and biomass, relative to the metal-contaminated sites. Amendment of the soils with metal-salts resulted in a decrease in microbial activity and biomass, as well as shifts in microbial community structure and function at each site. Soil microbial communities from each site were also observed to be sensitive to changes in soil pH as a result of metal-salt amendment; however, the magnitude of these pH-associated effects varied between soils. Microbial communities from each site did not converge on a structurally or functionally similar community following metal-salt amendment, indicating that other factors may be equally important in shaping microbial communities in soils. Among these factors, soil physiochemical parameters like organic matter and soil pH, which can both influence the bioavailability and toxicity of metals in soils, may be critical.     

How Does Conversion of Natural Tropical Rainforest Ecosystems Affect Soil Bacterial and Fungal Communities in the Nile River Watershed of Uganda?

Uganda''s forests are globally important for their conservation values but are under pressure from increasing human population and consumption. In this study, we examine how conversion of natural forest affects soil bacterial and fungal communities. Comparisons in paired natural forest and human-converted sites among four locations indicated that natural forest soils consistently had higher pH, organic carbon, nitrogen, and calcium, although variation among sites was large. Despite these differences, no effect on the diversity of dominant taxa for either bacterial or fungal communities was detected, using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Composition of fungal communities did generally appear different in converted sites, but surprisingly, we did not observe a consistent pattern among sites. The spatial distribution of some taxa and community composition was associated with soil pH, organic carbon, phosphorus and sodium, suggesting that changes in soil communities were nuanced and require more robust metagenomic methods to understand the various components of the community. Given the close geographic proximity of the paired sampling sites, the similarity between natural and converted sites might be due to continued dispersal between treatments. Fungal communities showed greater environmental differentiation than bacterial communities, particularly according to soil pH. We detected biotic homogenization in converted ecosystems and substantial contribution of β-diversity to total diversity, indicating considerable geographic structure in soil biota in these forest communities. Overall, our results suggest that soil microbial communities are relatively resilient to forest conversion and despite a substantial and consistent change in the soil environment, the effects of conversion differed widely among sites. The substantial difference in soil chemistry, with generally lower nutrient quantity in converted sites, does bring into question, how long this resilience will last.     

Soil and geography are more important determinants of indigenous arbuscular mycorrhizal communities than management practices in Swiss agricultural soils

Arbuscular mycorrhizal fungi (AMF) are ubiquitous soil fungi, forming mutualistic symbiosis with a majority of terrestrial plant species. They are abundant in nearly all soils, less diverse than soil prokaryotes and other intensively studied soil organisms and thus are promising candidates for universal indicators of land management legacies and soil quality degradation. However, insufficient data on how the composition of indigenous AMF varies along soil and landscape gradients have hampered the definition of baselines and effect thresholds to date. Here, indigenous AMF communities in 154 agricultural soils collected across Switzerland were profiled by quantitative real‐time PCR with taxon‐specific markers for six widespread AMF species. To identify the key determinants of AMF community composition, the profiles were related to soil properties, land management and site geography. Our results indicate a number of well‐supported dependencies between abundances of certain AMF taxa and soil properties such as pH, soil fertility and texture, and a surprising lack of effect of available soil phosphorus on the AMF community profiles. Site geography, especially the altitude and large geographical distance, strongly affected AMF communities. Unexpected was the apparent lack of a strong land management effect on the AMF communities as compared to the other predictors, which could be due to the rarity of highly intensive and unsustainable land management in Swiss agriculture. In spite of the extensive coverage of large geographical and soil gradients, we did not identify any taxon suitable as an indicator of land use among the six taxa we studied.     

Soil microbiome responses to the short‐term effects of Amazonian deforestation

Slash‐and‐burn clearing of forest typically results in increase in soil nutrient availability. However, the impact of these nutrients on the soil microbiome is not known. Using next generation sequencing of 16S rRNA gene and shotgun metagenomic DNA, we compared the structure and the potential functions of bacterial community in forest soils to deforested soils in the Amazon region and related the differences to soil chemical factors. Deforestation decreased soil organic matter content and factors linked to soil acidity and raised soil pH, base saturation and exchangeable bases. Concomitant to expected changes in soil chemical factors, we observed an increase in the alpha diversity of the bacterial microbiota and relative abundances of putative copiotrophic bacteria such as Actinomycetales and a decrease in the relative abundances of bacterial taxa such as Chlamydiae, Planctomycetes and Verrucomicrobia in the deforested soils. We did not observe an increase in genes related to microbial nutrient metabolism in deforested soils. However, we did observe changes in community functions such as increases in DNA repair, protein processing, modification, degradation and folding functions, and these functions might reflect adaptation to changes in soil characteristics due to forest clear‐cutting and burning. In addition, there were changes in the composition of the bacterial groups associated with metabolism‐related functions. Co‐occurrence microbial network analysis identified distinct phylogenetic patterns for forest and deforested soils and suggested relationships between Planctomycetes and aluminium content, and Actinobacteria and nitrogen sources in Amazon soils. The results support taxonomic and functional adaptations in the soil bacterial community following deforestation. We hypothesize that these microbial adaptations may serve as a buffer to drastic changes in soil fertility after slash‐and‐burning deforestation in the Amazon region.     

Actinobacterial Community Structure in Soils Receiving Long-Term Organic and Inorganic Amendments

The impact of long-term organic and inorganic amendments on the actinobacterial community in soils was studied. Denaturing gradient gel electrophoresis patterns based on the V3 region of 16S rRNA suggested that there was no significant difference between the communities occurring in the different amendments. However, analysis of the clone libraries of the actinobacterial communities by the use of multiple statistical approaches showed that these communities were significantly different from each other. Results showed that long-term organic and inorganic soil amendments did not significantly alter the overall phylogenetic diversity of the actinobacterial communities but did significantly change the community structure.     

Methanotrophic communities in Australian woodland soils of varying salinity

Despite their large areas and potential importance as methane sinks, the role of methane-oxidizing bacteria (MOB) in native woodland soils is poorly understood. These environments are increasingly being altered by anthropogenic disturbances, which potentially alter ecosystem service provision. Dryland salinity is one such disturbance and is becoming increasingly prevalent in Australian soils. We used microarrays and analysis of soil physicochemical variables to investigate the methane-oxidizing communities of several Australian natural woodland soils affected to varying degrees by dryland salinity. Soils varied in terms of salinity, gravitational water content, NO(3)-N, SO(4)-S and Mg, all of which explained to a significant degree MOB community composition. Analysis of the relative abundance and diversity of the MOB communities also revealed significant differences between soils of different salinities. Type II and type Ib methanotrophs dominated the soils and differences in methanotroph communities existed between salinity groups. The low salinity soils possessed less diverse MOB communities, including most conspicuously, the low numbers or absence of type II Methylocystis phylotypes. The differences in MOB communities suggest niche separation of MOB across varying salinities, as has been observed in the closely related ammonia-oxidizing bacteria, and that anthropogenic disturbance, such as dryland salinity, has the potential to alter MOB community and therefore the methane uptake rates in soils in which disturbance occurs.     

Efficacy of Aldicarb to Rotylenchulus reniformis and Biodegradation in Cotton Field Soils

The microbial degradation of aldicarb was examined in the greenhouse using soil from four cotton fields with a history of aldicarb use. The addition of aldicarb at 0.59 kg a.i./ha to natural soil increased Rotylenchulus reniformis numbers 6.6% in one soil and decreased R. reniformis numbers only 25.8% in another soil as compared to the corresponding natural soil without aldicarb. The use of increasing rates of aldicarb did not increase the efficacy of aldicarb in these soils. Rotylenchulus reniformis numbers were reduced 39.8, 22.6, and 6.8%, and increased 5.7% for aldicarb applied at 0.29, 0.59, 0.85, and 1.19 kg a.i./ha, respectively, in one natural soil. In another natural soil, R. reniformis numbers were reduced 42.5 and 21.9% for aldicarb applied at 0.29 and 1.19 kg a.i./ha, respectively, but increased 19.1 and 10.6% for aldicarb applied at 0.59 and 0.85 kg a.i./ha, respectively. Autoclaving the soils restored aldicarb toxicity in both soils, and R. reniformis numbers were reduced 96 and 99%, respectively, as compared to autoclaved soil without aldicarb. Bacterial populations were greater in the natural soils where aldicarb did not reduce R. reniformis numbers relative to the same soils that were autoclaved. However, no bacterial species was consistently associated with aldicarb degradation.     

Environmental causes and consequences of forest clearance and agricultural abandonment in central New York, USA

Aim Climate, topography and soils drive many patterns of plant distribution and abundance across landscapes, but current plant communities may also reflect a legacy of past disturbance such as agricultural land use. To assess the relative influences of environmental conditions and disturbance history on vegetation, it is important to understand how these forces interact. This study relates the geographical distribution of land uses to variation in topography and soils; evaluates the consequences of land‐use decisions for current forests; and examines the effects of agricultural land use on the chemical properties of forest soils. Location Tompkins County occupies 1250 km² in central New York's Finger Lakes region. Like much of eastern North America, this area underwent forest clearance for agriculture during the 1800s and widespread field abandonment and forest recovery during the 1900s. The current landscape consists of a patchwork of forests that were never cleared, forests that developed on old fields and active agricultural lands. Methods We investigated relationships among topography, soils and land‐use decisions by gathering information about land‐use history, slope, aspect, elevation, soil lime content, soil drainage and accessibility in a geographic information system (GIS). To assess the effects of agriculture on forest soil chemistry, we measured pH, organic matter content and extractable nutrient concentrations in field‐collected soil samples from 47 post‐agricultural and uncleared forests. Results Steeper slopes, less accessible lands and lower‐lime soils tended to remain forested, and farmers were more likely to abandon fields that were steeper, farther from roads, lower in lime and more poorly drained. Slope had by far the greatest impact on patterns of clearance and abandonment, and accessibility had a surprisingly strong influence on the distribution of land uses. The effects of other factors varied more, depending for example on location within the county. Current forest types differed accordingly in topography and soil attributes, particularly slope, but they also showed much overlap. Post‐agricultural and uncleared forest soils had similar chemical properties. Forests on lands abandoned from agriculture 80–100 years before had slightly higher pH and nutrient concentrations than adjacent, uncleared forests, but these changes were small compared to environmental variation across the county. Main conclusions Despite differential use of lands according to their topography and soils, the substantial influence of accessibility and the relatively small scale of land‐use decisions allowed for broad similarity among forest types. Thus, the topography and soil differences created by land‐use decisions probably contribute little to landscape‐level patterns of diversity. Subtle changes in forest soil chemistry left from past agriculture may nevertheless affect plant distribution and abundance at finer scales.     

Effects of Soil Nutrient Heterogeneity and Earthworms on Aboveground Biomass of Experimental Plant Communities

Soil nutrients are commonly heterogeneously distributed and earthworms are one of the most common soil organisms. While effects of both soil nutrient heterogeneity and earthworms have been well studied, their interactive effect on plant community productivity has rarely been tested. In a greenhouse experiment, we constructed experimental plant communities by sowing seed mixtures of four grasses, two legumes and two forbs in either a heterogeneous soil consisting of low and high nutrient soil patches or a homogeneous soil where the low and high nutrient soil patches were evenly mixed. The earthworm Eisenia fetida was either added to these soils or not. Aboveground biomass of the whole communities, grasses and legumes did not differ between the homogeneous and heterogeneous soils or between the soils with and without earthworms. However, soil nutrient heterogeneity reduced aboveground biomass of forbs, and such an effect did not interact with earthworms. In response to soil heterogeneity and earthworms, biomass ratio of the three functional groups showed similar patterns as that of their biomass. At the patch level, aboveground biomass of the whole community, grasses and legumes were greater in the high than in the low nutrient soil patches within the heterogeneous soil. A similar pattern was found for the forbs, but this was only true in the absence of earthworms. Our results suggest that soil nutrient heterogeneity and earthworms may not influence aboveground biomass of plant communities, despite the fact that they may modify the growth of certain plant functional groups within the community.     

Soil microbial community responses to altered lignin biosynthesis in Populus tremuloides vary among three distinct soils

The development and use of transgenic plants has steadily increased, but there are still little data about the responses of soil microorganisms to these genetic modifications. We utilized a greenhouse trial approach to evaluate the effects of altered stem lignin in trembling aspen (Populus tremuloides) on soil microbial communities in three soils which differed in their chemical and physical properties; they included a sandy loam (CO-Colorado), a silt loam (KS-Kansas), and a clay loam (TX-Texas). Three transgenic aspen lines were developed from a natural clone common to the Great Lakes region of North America. The concentrations of stem lignin concentrations were reduced by 35% (Line 23), 40% (Line 141) and 50% (Line 72). Line 72 and Line 141 also had a 40 and 20% increase in syringyl-type stem lignin, respectively. Indirectly, these modifications resulted in increased (5–13%) and decreased (−5 to −57%) levels of root production across the lines and soil types. Responses of the soil microbial communities were investigated using: phospholipid fatty acids (PLFA), neutral lipid fatty acids (NLFA), and 3) extracellular enzyme assays. PLFA analyses indicated that there were large differences in microbial community composition between the three soils. Similarly, there were large differences in total NLFA between soils, with the KS soils having the highest amount and CO the lowest. Enzyme activities did not differ between soils, except for cellubiohydrolase, which was highest in CO soil. Across all three soils, responses to the four genetic lines were not consistent. Interactions between soil type and genetic line make it difficult to assess the potential ecological impacts of transgenic aspen on soil microbial communities and their associated functions. Given these interactions, field trials with transgenic aspen should encompass the wide range of soils targeted for commercial planting in order to determine their effect(s) on the resident soil microbial community. Responsible Editor: Barbara Wick