Sole Carbon Source Utilization Research Articles

Effects of contamination of single and combined cadmium and mercury on the soil microbial community structural diversity and functional diversity

To assess the effects of single and combined pollution of cadmium (Cd) and mercury (Hg) on soil microbial community structural and functional diversities, an incubation experiment was conducted, by employing two soils, namely, the marine sediment silty loam soil and the yellowish-red soil, in which five levels of Cd, Hg and Cd and Hg in combination were added. After being incubated for 56 days, the phospholipid fatty acids (PLFAs) profile and sole carbon source utilization pattern (BIOLOG) of the samples were tested. The results showed that the composition of the microbial communities changed significantly at different levels of metals application. The principal component analyses (PCA) of PLFAs indicated that the structure of the microbial community was also significantly altered with increasing levels of metals, with increasing PLFAs biomarkers for fungi and actinomycetes, and increasing ratio of Gram-positive to Gram-negative bacteria. Sole carbon source utilization pattern analysis revealed that single and combined application of Cd and Hg inhibited significantly the functional activity of soil microorganisms, the functional diversity indices [Richness (S), Shannon-Wiener indices (H) and Evenness (EH)] were significantly lower in polluted soils than those in non-polluted soils, which also significantly altered with increasing levels of metals. PCA for the sole carbon source utilization pattern also indicated that the metal contamination could result in a variable soil microbial community. The results revealed that the combination of Cd and Hg had higher toxicity to soil microbial community structural and functional diversities than the individual application of Cd or Hg.

Changes of Soil Microbiological Characteristics After Solidago canadensis L. Invasion

The relationship between Solidago canadensis L. invasion and soil microbial communities was studied across the invasive gradients varying from 0 to 40, 80, and 100% coverage of S. canadensis. The results showed both soil microbial biomass C (C mic) and N (N mic) increased as the coverage of S. canadensis increased. Soil microbial quotient C mic/C org (microbial biomass C/organic C) tended to increase linearly with the coverage of S. canadensis. Soil basal respiration (BR) also showed a similar trend. The soil respiratory quotient qC0 2 decreased with S. canadensis invasion, and remained at quite a constantly low level in the invasive soils. Sole carbon source utilization profiles analyses indicated that S. canadensis invasion tended to result in higher microbial functional diversity in the soil. Average utilization of specific substrate guilds was highest in the soil with S. canadensis monoculture. Principle component analysis of sole carbon source utilization profiles further indicated that microbial functional diversity in the soil with S. canadensis monoculture was distinctly separated from those soils in the native area and the ecotones. In conclusion, S. canadensis invasion improved soil microbial biomass, respiration and utilization of carbon sources, and decreased qC0 2, thus created better soil conditions, which in turn were more conducive to the growth of S. canadensis.

Phenotypic and molecular characterization of rhizobacterium Burkholderia sp. strain R456 antagonistic to Rhizoctonia solani, sheath blight of rice

The effect of rhizobacterium Burkholderia sp. strain R456 on the inhibition of Rhizoctonia solani, sheath blight of rice was examined. Results from this study indicated that strain R456 not only suppressed the in vitro mycelial growth of R. solani, but also reduced the incidence and severity of rice sheath blight under greenhouse conditions. However, similar to plant pathogenic strain LMG 1222T of Burkholderia cepacia, the type species of the genus, infiltration of tobacco leaves with cell suspension of strain R456 resulted in typical hypersensitivity reactions while the two bacterial strains were unable to cause disease symptoms on rice seedlings. The fatty acid methyl ester profile, sole carbon source utilization, and biochemical tests confirmed that the antagonistic rhizobacterium R456 is a member of the genus Burkholderia. Furthermore, strain R456 was differentiated from B. cepacia LMG 1222T and was identified as Burkholderia seminalis based on recA gene sequence analysis and multilocus sequence typing. In addition, this rhizobacterium had a lower proteolytic activity compared with that of the pathogenic B. cepacia LMG 1222T while no cblA and esmR marker genes were detected for the two bacterial strains. Overall, this is the first characterization of rhizobacterium B. seminalis that protected rice seedlings from infection by R. solani.

Nutritional constraints on displacement of Fusarium pseudograminearum from cereal straw by antagonists

Displacement of the fungus Fusarium pseudograminearum from stubble by antagonists is a potential means of biocontrol of crown rot in cereals. The role of carbon and nitrogen nutrition in interactions between the pathogen and the antagonists Fusarium equiseti, Fusarium nygamai, Trichoderma harzianum and the non-antagonistic straw fungus Alternaria infectoria was investigated. Sole carbon source utilization patterns on Biolog plates were similar among the three Fusarium species, suggesting a possible role for competition. However, carbon niche overlap was unlikely to be important in antagonism by T. harzianum. Straw medium supplemented with sugars generally reduced the inhibitory effect of antagonists on growth of F. pseudograminearum in dual culture, indicating that availability of simple carbon sources does not limit antagonism. Adding nitrogen as urea, nitrate or ammonium to straw medium had little effect on antagonism by F. equiseti and F. nygamai, but ammonium addition removed the inhibitory effect of T. harzianum on growth of F. pseudograminearum. Displacement of F. pseudograminearum from straw by all fungi in a Petri dish assay was greater when urea or nitrate was used as a nitrogen source than with ammonium. All forms of nitrogen significantly increased displacement of F. pseudograminearum from straw under simulated field conditions when straws were either inoculated with T. harzianum or exposed to resident soil microbes. However, in 2 out of 3 experiments urea and nitrate were more effective than ammonium. The results suggest that availability of nitrogen, but not carbon, is limiting the activities of antagonists of F. pseudograminearum in straw, and the way nitrogen is applied can influence the rate of displacement and mortality of the pathogen in host residues.

Phytoremediation of Oilfield Sludge After Prepared Bed Bioremediation Treatment

A field-scale experiment was carried out to compare the effectiveness of five plant species in the remediation of oily sludge. Alfalfa, tall fescue, and soybean substantially increased the removal rate of oil and grease (O&G) after 120 days of remediation. Of these, soybean treatment showed the highest removal rate of 34.2% compared with only 13.7% in the unplanted control plot. In addition to assisting with phytoremediation, soybean can also be used for energy production, for example in the production of biodiesel. Furthermore, microbial counts and community level physiological profiling using Biolog sole carbon source utilization tests were used to investigate the effect of plants on the microbial community of oily sludge. Plants selectively increased microbial counts in the rhizosphere and O&G concentrations of the sludge were negatively correlated with counts of TPH (total petroleum hydrocarbon) degraders. The acute biotoxicity of the sludge was also tested by the bacterial luminescence method and alfalfa treatments decreased the biological toxicity of the sludge compared with the unplanted control.

Suppression of disease in tomato infected by Pythium ultimum with a biosurfactant produced by Pseudomonas koreensis

The use of biosurfactants is a promising alternative in biological control of zoospore-producing oomycetes, which are a major plant pathogen world-wide in a wide variety of crops. Oomycetes are of particular concern in closed hydroponic cultivation systems. The present study investigated the efficacy of a biosurfactant produced by Pseudomonas koreensis and added as a crude extract against the oomycete Pythium ultimum in hydroponic tomato cultivation. A significant reduction in disease was observed. Biosurfactant addition did not affect the indigenous root microflora when evaluated as sole carbon source utilisation. Chemical analysis, using electrospray hybrid mass spectrometry (ESI-MSMS), of the biosurfactant indicated it to be lokisin, a cyclic lipopeptide. These results confirm that biosurfactants are important in developing sustainable biological control strategies for oomycetes.

Micromonospora tulbaghiae sp. nov., isolated from the leaves of wild garlic, Tulbaghia violacea.

A novel actinomycete, strain TVU1(T), was isolated from leaves of the indigenous South African plant Tulbaghia violacea. Applying a polyphasic approach, the isolate was identified as a member of the genus Micromonospora. Phylogenetic analysis of the 16S rRNA gene sequence showed that strain TVU1(T) was most closely related to Micromonospora echinospora DSM 43816(T). However, phylogenetic analysis based on gyrB gene sequences showed that strain TVU1(T) was most closely related to the type strains of Micromonospora aurantiaca and Micromonospora chalcea. DNA-DNA relatedness values between strain TVU1(T) and the type strains of M. echinospora, M. aurantiaca and M. chalcea were 7.6+/-4.5, 45.9+/-2.0 and 60.9+/-4.5 %, respectively. Strain TVU1(T) could be distinguished from the type strains of all three of these species by several physiological characteristics, such as colony colour, NaCl tolerance, growth temperature range and sole carbon source utilization pattern. Strain TVU1(T) (=DSM 45142(T)=NRRL B-24576(T)) therefore represents a novel species for which the name Micromonospora tulbaghiae sp. nov. is proposed.

One-dimensional metric for tracking bacterial community divergence using sole carbon source utilization patterns

Community level physiological profiling (CLPP) has become a popular method to characterize and track changes in heterotrophic bacterial communities. Although the CLPP method is a straight forward laboratory protocol which yields large amounts of functional information, the amount of data obtained can become overwhelming and often requires some type of multivariate analysis method for ordination and interpretation. Multivariate analysis can be challenging and requires a significant statistics background along with an understanding of the inferences and biases each multivariate analysis method incurs. This paper presents and evaluates a new approach to analyzing sole carbon source utilization data. A method is described which provides a one-dimensional metric derived from standard CLPP data (BIOLOG™ EcoPlate data). The one-dimensional community metric was derived using normalized Euclidean distances and shifts in the carbon source utilization patterns. The one-dimensional community metric did not provide all of the information of classical approaches such as principle component analysis (PCA) or guild grouping analysis; however, it was found to be more easily implemented and interpreted when analyzing the plate data. Validation of this approach is demonstrated using data acquired to track the divergence of bacterial communities in wetland mesocosm systems after an experimentally controlled disturbance. If the objective is to investigate community shifts over time the one-dimensional community divergence metric can be a useful tool.

Herbidospora osyris sp. nov., isolated from surface-sterilized tissue of Osyris wightiana Wall. ex Wight

An endophytic actinomycete, strain YIM 65070(T), was isolated from surface-sterilized tissue of Osyris wightiana Wall. ex Wight collected from Yunnan province, south-west China, and characterized by using a polyphasic approach. Strain YIM 65070(T) had morphological and chemotaxonomic markers that were consistent with its classification in the genus Herbidospora. Phylogenetic analysis based on almost complete 16S rRNA gene sequences indicated that strain YIM 65070(T) was phylogenetically very closely related to Herbidospora cretacea IFO 15474(T). DNA-DNA hybridization experiments confirmed the separate genomic status of strains YIM 65070(T) and H. cretacea DSM 44071(T). Moreover, strain YIM 65070(T) could be distinguished from H. cretacea DSM 44071(T) by differences in several phenotypic characteristics such as tolerance to NaCl, degradation activity, utilization of sole carbon and nitrogen sources and the cellular fatty acid contents. On the basis of phenotypic and phylogenetic evidence, strain YIM 65070(T) was identified as a novel species of the genus Herbidospora, for which the name Herbidospora osyris sp. nov. is proposed, with YIM 65070(T) (=CCTCC AA 208019(T)=DSM 45214(T)) as the type strain.

Soil Microbial Community Composition and Diversity in the Rhizosphere of a Chinese Medicinal Plant

Rehmannia glutinosa is an important medicinal plant, but there is a serious problem of decreasing productivity with its continuous cropping on the same land. We hypothesize some relationships between this problem and the disturbed soil ecosystem. In this work, two community‐based microbiological measurements, community‐level physiological profiling (CLPP) using Biolog sole carbon (C) source utilization tests and phospholipid ester–linked fatty acid (PLFA) profiles, were used to evaluate soil microbial community function and composition of different R. glutinosa cropping soils. Field investigation showed that the problems with continuous cropping occurred not only in 2‐year continuous fields but also in 5‐year rotation fields. Soil basal respiration and metabolic quotient were significantly greater in R. glutinosa cropping soils than in the noncropping controls. In contrast, the Shannon index from the Biolog data set was lower in R. glutinosa cropping soils. Both CLPP‐ and PLFA‐based principal component analyses (PCA) showed distinct groupings of soil microbial communities in R. glutinosa rhizosphere, and 11 PLFAs representing different microbes were identified from the principal component scores of PLFAs. Among these, an abundance of PLFA 18:2ω6,9, which is a biomarker of soil fungi, was significantly higher in R. glutinosa cropping soils than control soils. These results suggest an alteration of soil microbial community following R. glutinosa cropping, and this might be an important reason for the constraints associated with continuous cropping.

Co-composting of manure with fat, oil, and grease: Microbial fingerprinting and phytotoxicity evaluation

Sole carbon source utilization profiles to characterize compost maturity were evaluated in reference to several other physicochemical and biological maturity indices. The results suggested that the addition of fat, oil, and grease (FOG) had a significant effect on the biological processes in the sample piles when compared to the control pile. Additionally, principal components analysis of the patterns and the levels of microbial activity indicate that microbial communities differentiate in response to FOG additions from 1 to 20 L/m3. However, between 10 and 20 L/m3, no recognizable differences were found between the control and the FOG amendment communities. Biolog data indicates a shift in the structure and function of the microbial community in compost with high FOG additions, which may be a useful indicator of high functional diversity and evenness during composting processes. Finally, the germination index (GI) of lettuce increased from 9% in the control to 100% in the FOG amended compost. However, the addition of high amounts of FOG might in turn inhibit seed germination and root growth because of the high pH and electrical conductivity (EC), and the volatilization of NH3. From the present results, 10 L/m3 was found to be the optimum FOG amendment rate for manure compost. These amendment rates are empirical and may be regarded as potential guidelines to agricultural practitioners.

Utilisation of Carbon Sources by Pythium, Phytophthora and Fusarium Species as Determined by Biolog® Microplate Assay

This study examined the metabolic activity of pure cultures of five root pathogens commonly found in closed hydroponic cultivation systems (Phytophthora cryptogea (PC), Phytophthora capsici (PCP), Pythium aphanidermatum (PA), Fusarium oxysporum f.sp. radicis-lycopersici (FORL) and Fusarium solani (FS)) using sole carbon source utilisation in order to develop effective biocontrol strategies against these pathogens. Aliquots of 150 µL of the mycelial suspension were inoculated in each well of GN2 microtitre plates. On the basis of average well colour development and number of positive wells, the pathogens were divided into two groups, (i) PA and FORL and (ii) PC, PCP and FS. Group (i) was characterised by a short lag-phase, a rapid exponential phase involving almost all carbon sources offered and a long stationary phase, while group (ii) had a more extended lag-phase and a slower utilisation rate of the carbon sources offered. The three isolates in group (ii) differed significantly during their exponential phase. The lowest utilisation rate of carbon sources and number of sources utilised was found for PCP. Of the major group of carbon sources, six carbohydrates, three carboxylic acids and four amino acids were rapidly used by all isolates tested at an early stage. The carbon sources gentibiose, α-D-glucose, maltose, sucrose, D-trehalose, L-aspartic acid, L-glutamic acid, L-proline persisted to the end of the exponential phase.Moreover, similarities between the metabolic profiles of the tested pathogen and the those of the resident microflora could also be found. These findings are of great importance as regards the role of the resident microflora in the biocontrol.

Impact of Elevated O3 on Soil Microbial Community Function Under Wheat Crop

This study was initiated to explore the effects of ozone (O-3) exposure on potted wheat roots and soil microbial community function. Three treatments were performed: (1) Air with daily averaged O-3 concentration of 4-10 ppb (control situation, CK), (2) Air plus 8 h averaged O-3 concentration of 76.1 ppb (O-3-1), and (3) Air plus 8 h averaged O-3 concentration of 118.8 ppb (O-3-2). In treatments with elevated O-3 concentration (O-3-1 and O-3-2), the root and shoot biomass were reduced by 25% and 18%, respectively, compared to the control treatment (CK). On the other hand, root activity was significantly reduced by 58% and 90.8% in the O-3-1 and O-3-2 treatments, respectively, compared to CK. The soil microbial biomass was significantly reduced only in the highest O-3 concentration (O-3-2 treatment) in the rhizosphere soil. Soil microbial community composition was assessed under O-3 stress based on the changes in the sole carbon source utilization profiles of soil microbial communities using the Biolog (TM) system. Principal component analysis showed that there was significant discrimination in the sole-carbon source utilization pattern of soil microbial communities among the O-3 treatments in rhizosphere soil; however, there was none in the bulk soil. In rhizosphere soil, the functional richness of the soil microbial community was reduced by 27% and 38% in O-3-1 and O-3-2 treatments, respectively, compared to CK. O-3-2 treatment remarkably decreased the Shannon diversity index of soil microbial community function in rhizosphere soil, but the O-3-1 treatment did not. In the dominant microorganisms using carbon sources of carbohydrates and amino acids groups were significantly reduced by an elevated O-3 concentration in the rhizosphere soil. Our study shows that the elevated ozone levels may alter microbial community function in rhizosphere soil but not in the bulk soil. Hence, this suggests that O-3 effects on soil microbes are caused by O-3 detriments on the plant, but not by the O-3 direct effects on the soil microbes.

Catabolic profiles of soil fungal communities along a geographic climatic gradient in Israel

The great distances that typically separate different climatic zones have previously restricted the investigation of climatic controls over soil microbial function to only short-scale gradients, or alternatively, to the investigation of extreme instead of real gradients. In this study, we comparatively assessed sole carbon source utilization profiles and resultant catabolic diversity levels of soil fungal communities along a geographically continuous steep climatic gradient, stretching from the Upper Galilee in the north of Israel to the Negev Desert in the south. Four sites along the gradient were studied, representing humid-Mediterranean, Mediterranean, semi-arid and arid climate types, and they were characterized by a mean annual rainfall of 780, 537, 300, and 90 mm, respectively. The relationships between abiotic soil characteristics and fungal activity parameters (basal respiration, biomass, and the metabolic quotient qCO 2) as well as fungal substrate utilization profiles and functional diversity were explored in the context of climate and seasonality (rainy versus dry seasons). To make an ecologically relevant assessment of fungal activity in soil, a MicroResp™ microrespiratory system capable of analyzing whole-soil samples was modified to allow, for the first time, the testing of fungal utilization of low-solubility carbon substrates, alongside other major plant-derived substrates, reflective of the soil environment. The accurate profiling of substrate utilization in the calcareous soils comprising this Mediterranean gradient could not have been accomplished without the correction of measured CO 2 evolution data, which were biased due to CaCO 3–CO 2–H 2O equilibria reactions. The correction of the data was conducted according to a protocol presented in the preceding article of this series. The utilization potential of all 14 substrates tested was higher during the dry than during the rainy season, particularly in the Mediterranean sites, with polymeric substrates being utilized preferentially in the arid sites in comparison with the Mediterranean sites. The distinctive approach exercised in this study enabled us to make a relevant ecological interpretation, particularly in face of the prospect of fungi being responsible for the bulk of recalcitrant organic matter decomposition in soil.

Microbial community diversity in the profle of an agricultural soil in northern China

The soil microorganisms at different depths play an important role in soil formation, ecosystem biogeochemistry, recycling of nutrients, and degradation of waste products. The aims of this study were to observe the microbial diversity in the profile of an agricultural soil in northern China, and to research the correlation between soil microbes and geochemistry. First, the soil geochemistry of the profile was investigated through 25 chemical elements. Secondly, the various physiological groups of microorganisms were studied by traditional culture methods. Thirdly, the functional diversity on sole carbon source utilization (SCSU) was evaluated by the BIOLOG system. Finally, the correlation between the soil microbial diversity and geochemistry was analyzed statistically. The results showed that the amounts and proportions of various physiological groups of microorganisms changed with depth. The bacterial functional diversity on SCSU decreased with increasing depth, but evenness of the substrate utilization increased. Although the microbial metabolic diversity was different at every depth, it could be classified into three main groups by principal component analysis and cluster analysis. The various physiological groups of microorganisms showed remarkable correlation with relevant soil chemical elements. The sensitive microbial indicators of soil health were expected to be screened out from actinomyces or ammonifying bacteria.

Influence of Tea Cultivation on Soil Microbial Biomass and Substrate Utilization Pattern

The study was conducted to evaluate the effect of tea cultivation on soil microbial biomass and community structure. Soil pH, extractable aluminum (Al), organic carbon (Corg) and total nitrogen were considerably modified by tea cultivation. Long‐term tea cultivation resulted in the increase of microbial biomass C (Cmic), microbial biomass N (Nmic), and basal respiration. The metabolic quotient declined as the tea cultivation age increased. The adjacent citrus orchard soil showed a higher Cmic/Corg ratio than the tea orchard soils. Microtitration plates with 21 carbon sources and two different pH levels (4.7 and 7.0) were used to determine the substrate utilization pattern of these soils. The average well color development (AWCD) of the carbon sources in the plates did not vary in a consistent manner with the microbial biomass. Multivariate analysis of sole carbon source utilization pattern demonstrated that land‐use history had a significant effect on substrate utilization pattern. The pH 4.7 characterization medium can increase the discrimination of this technique and is more adequate than the conventional neutral medium for the tea orchard soils.

Effect of heavy metals on substrate utilization pattern, biomass, and activity of microbial communities in a reclaimed mining wasteland of red soil area

The microbial biomass, basal respiration, and substrate utilization pattern in a copper mining wasteland of red soil area, southern China, were investigated, and indicated that soil microflora were obviously affected by heavy metals. Microbial biomass and basal respiration were negatively affected by comparatively high heavy metal levels. Two important microbial ecophysiological parameters, namely, the microbial biomass C ( C mic)/microbial biomass N ( N mic) ratio and the metabolic quotient ( qCO 2) were significantly correlated to heavy metal stress. There was a significant decrease in the C mic/ N mic ratio and an increase in the metabolic quotient with increasing metal concentration. Multivariate analysis of Biolog data for sole carbon source utilization pattern demonstrated that heavy metal pollution had a significant impact on microbial community structure and functional diversity. All the results showed that soil microbiological parameters could have great potential as sensitive, effective, and liable indicators of the stresses or perturbations in soils of mining ecosystems.

Rhizobacterial community-level, sole carbon source utilization pattern affects the delay in the bacterial wilt of tomato grown in rhizobacterial community model system

Characterizing rhizomicrobial community structure is important to our understanding of the mechanisms of suppressive soils towards soilborne plant diseases. We investigated whether the bacterial community structure, i.e., the number of the constituent bacterial strains and the community-level, sole carbon source utilization pattern of rhizobacteria estimated by BIOLOG EcoPlates, affects bacterial wilt of tomato. To assess their impact on the bacterial wilt, we used 15 artificial soil systems into which 5–20 rhizobacterial isolates from a disease-suppressive soil were inoculated. Although most of the tomato plants wilted by 16 days after pathogen inoculation, significant negative relationships were observed between the number of wilted plants, the number of the bacterial strains and the number of carbon sources that the rhizobacterial community was able to utilize. BIOLOGs showed that several carbon sources were utilized by the pathogen but not by the rhizobacterial community from the fastest-wilting treatments, suggesting that competition between the pathogen and the other rhizobacteria for carbon sources played an important role in suppressing the growth of the pathogen.

Analysis and interpretation of community-level physiological profiles in microbial ecology

A rapid, community-level approach for assessing patterns of sole carbon source utilization by mixed microbial samples has been used increasingly to study microbial community dynamics. The method involves direct inoculation of environmental samples into Biolog microtiter plates, and uses color formation from reduction of a tetrazolium dye to assess utilization of 95 separate sole carbon sources during a 2–7 day incubation period. This approach, called community-level physiological profiling, has been effective at distinguishing spatial and temporal changes in microbial communities. Effective analysis of the multivariate profiles of carbon source utilization requires separation of effects caused by differences in inoculum density (i.e. overall rate of color development) from effects caused by differences in the types or activities of organisms present (i.e. relative rates, or pattern, of carbon source utilization). Further experimental studies are required to better define what fraction of the original inoculum responds in the assay, and if the profiles provide structural and/or functional information.

Defoliation and fertiliser influences on the soil microbial community associated with two contrasting Lolium perenne cultivars

The influence of repeated defoliation on soil microbial community (SMC) structure and root turnover was assessed in two contrasting Lolium perenne cultivars (AberDove and S23) grown in fertilised (+F) and non-fertilised (NF) soil. BiOLOG sole carbon source utilisation profiles (SCSUPs) indicated consistently greater potential carbon utilisation in defoliated (+D) compared to non-defoliated (ND) soils regardless of cultivar and fertiliser, and was accounted for in a variety of substrate groups (sugars, carboxylic, amino and phenolic acids). Potential carbon utilisation was also stimulated in +F compared to NF soils, primarily through increased potential utilisation of carboxylic acids. PLFA indicators for the bacterial biomass did not significantly differ between cultivar, soil fertilisation, or defoliation. Defoliated swards grown in fertilised soil (+F+D) had a higher fungal:bacterial ratio and a greater bacterial stress index (cy19:0/18:1w7c), compared to that of +F ND, NF ND and NF+D, and regardless of cultivar. Overall SMC structure (canonical variate (CV) analysis of PLFAs) discriminated based on cultivar, defoliation and soil fertilisation. Primary discrimination of the SMCs could be related to differences in root density and total plant biomass, and in the case of NF soils, secondary community shifts, evident with defoliation, related to root disappearance over the growing season. Despite the strong common effects of defoliation, and to a lesser extent soil fertilisation, cultivar specific drivers of the soil microbial community were maintained, resulting in consistent, but subtle, discrimination of the SMC associated with the contrasting L. perenne cultivars.