Functional Diversity Of Soil Bacteria Research Articles

Soil bacterial activity and functional diversity as indicators of recultivation of alkaline settlements of a ‘Solvay’ process

PurposeMany industries continuously produce large volumes of alkaline residues. After recultivation, former landfills can be an important element providing ecosystem services in highly urbanised areas.Materials and methodsWe studied the relationship between vegetation and soil bacterial characteristics using Biolog® ECO plates on recultivated areas of the Solvay heaps, and participation of invasive species in plant community in progressive succession.Results and discussionBacterial activity and functional diversity indices were correlated with soil physicochemical properties (soil organic matter content, water holding capacity, total phosphorus content, and soil pH). Plots with a higher total number of vascular plant species, including forest floor species, and a higher Shannon–Wiener index of vegetation diversity H'plant, were characterised by a higher amino acid utilisation by soil bacteria. Soil bacteria CLPP (community-level physiological profiles) were most influenced by soil physical and chemical properties, but also by the proportion of invasive species in the total number of plant species. In conclusion, soil physical and chemical properties dominate vegetation characteristics in shaping the functional diversity of soil bacteria. Invasive species may be an influential component of ecosystems during spontaneous succession of degraded soils.

Diversity and activity of soil biota at a post-mining site highly contaminated with Zn and Cd are enhanced by metallicolous compared to non-metallicolous Arabidopsis halleri ecotypes.

Hyperaccumulators' ability to take up large quantities of harmful heavy metals from contaminated soils and store them in their foliage makes them promising organisms for bioremediation. Here we demonstrate that some ecotypes of the zinc hyperaccumulator Arabidopsis halleri are more suitable for bioremediation than others, because of their distinct influence on soil biota. In a field experiment, populations originating from metal-polluted and unpolluted soils were transplanted to a highly contaminated metalliferous site in Southern Poland. Effects of plant ecotypes on soil biota were assessed by measurements of feeding activity of soil fauna (bait-lamina test) and catabolic activity and functional diversity of soil bacteria underneath A. halleri plants (Biolog® ECO plates). Chemical soil properties, plant morphological parameters, and zinc concentration in shoots and roots were additionally evaluated. Higher soil fauna feeding activity and higher bacterial community functional diversity were found in soils affected by A. halleri plants originating from metallicolous compared to non-metallicolous ecotypes. Differences in community-level physiological profiles further evidenced changes in microbial communities in response to plant ecotype. These soil characteristics were positively correlated with plant size. No differences in zinc content in shoots and roots, zinc translocation ratio, and plant morphology were observed between metallicolous and non-metallicolous plants. Our results indicate strong associations between A. halleri ecotype and soil microbial community properties. In particular, the improvement of soil biological properties by metallicolous accessions should be further explored to optimize hyperaccumulator-based bioremediation technologies.

Effects of Nutrient Levels and Rice Cultivation on Taxonomic and Functional Diversity of Bacterial Communities in Flooded Soils of the Hanon Maar Crater, Korea

Agricultural land use may deteriorate soil bacterial diversity and function in an agroecosystem. This study aimed to explore the impact of agricultural disturbance on the taxonomic and functional diversity of soil bacteria using a high-throughput sequencing method. We examined the bacterial community diversity in five types of flooded soils in the Hanon Maar Crater from two types of canals characterized by different nutrient levels and three field types with a different rice cultivation history. Proteobacteria (43.2%), Chloroflexi (19.8%), Acidobacteria (15.8%), Actinobacteria (5.1%), and Nitrospirae (5.0%) were the dominant phyla (>5%). The relative abundance of Actinobacteria was 7.1 times greater in the abandoned fields than in the polluted canal. Alpha diversity indices of taxonomic diversity showed strong negative correlations with C, N, and NH4+ levels. The 1.7-fold greater number of operational taxonomic units (OTUs) in abandoned fields than in paddy fields may be caused by factors other than nutrients. Functional analysis revealed that 11 putative functions, including cellulolysis and ligninolysis, were significantly affected by soil management. Functional diversity indices showed negative correlations with electrical conductivity (EC) and NH4+. Nitrogen input had a greater effect on bacterial taxonomic diversity than on functional diversity. Available P was positively correlated with the diversity indices. Taken together, these results suggest that keeping land fallow for more than 5 years and monitoring of C, N, and P levels are practical approaches for restoring taxonomic diversity but not functional diversity of soil bacteria. Our study demonstrated a decoupled response of taxonomic and functional diversity to rice cultivation, highlighting the necessity of further studies on the impact of decoupling on the stability of ecosystem functioning.

Genetic and functional diversity of soil bacteria and fungi from different microhabitats in a karst region in Southern China

Little is known about the difference between bacterial and fungal genetic and functional diversity in karst regions of south China. In this study, the genetic and functional diversity of bacteria and fungi in nine types of soil microenvironments in the karst region in Maolan National Nature Reserve in Guizhou were investigated by PCR-DGGE (Denaturing Gradient Gel Electrophoresis) and BIOLOG EcoPlates. Maolan National Nature Reserve is a UNESCO Biosphere Reserve and plays an important role in protecting the karst forest ecosystem and rare and endangered wild animals and plants in central Asia. The results showed that the diversity of both bacteria and fungi was high and the main factors influencing the diversity of bacteria and fungi were different. The bacterial community structure from different microhabitats under the same vegetation type had higher similarity than similar microhabitats in different vegetation types, which could indicate that the bacterial community structure was mainly controlled by vegetation. For fungi, similar microhabitat species under different vegetation types had higher similarities than different microhabitats species under the same vegetation type, which could indicate that the fungal community structure is mainly controlled by microhabitats. In addition, the metabolic patterns of similar microhabitats in different vegetation were different, while the metabolic patterns of different microhabitats in the same vegetation were not obviously different. In conclusion, the effect of vegetation types on soil microbial functional diversity was greater than that of microhabitats, and this difference was reflected by the different degrees of influence on soil microbial genetic diversity and community structure.

Effects of novel bioorganic fertilizer application on soil enzymes and bacterial community in multi-site rice paddies in China

Application of a novel bioorganic fertilizer (BIO) has been effectively used to inhibit weeds in rice paddies. To identify changes in soil bacterial community and enzymes in response to BIO treatments, field experiments were carried out in five major rice-growing areas in China. The dominant phylogenetic groups recorded included Proteobacteria, Actinobacteria, Bacteroidetes, Firmicutes and Acidobacteria. Anaeromyxobacter, Bacteroides, Bifidobacterium, Escherichia- Shigella, Geobacter and Haliangium were significantly different between BIO-treatment and untreated control and aided in general function (R), amino acid transport, metabolism (E) and transcription (K) clusters. The soil chemical properties and enzyme activities were less affected by BIO at these study sites. RDA analysis showed that soil bacterial community had a significant positive correlations among northern latitude, eastern longitude, exchangeable K, total K, total P, soil pH, and total N, except for organic matter, hydrolytic N and extractable P. Overall, our work showed that application of BIO does not alter the main community structure and functional diversity of soil bacteria in rice paddies and should be encouraged for use as a sustainable weed management strategy.

Soil Chemical Properties and Biological Processes Under Pine Trees With and Without Dendroctonus Bark Beetle Infestation

ABSTRACT Pine forests are highly appreciated for the ecosystem services and raw materials they provide to society. However, insect pests are a constant threat. Bark beetles of the genus Dendroctonus are responsible for the high mortality that prevails in pine forests. Studies suggest that their presence can be related to changes in physicochemical and biological soil’s properties. The question is: How do the chemical properties of the soil and the biological processes change in pine trees with and without Dendroctonus? We analyze variables such as pH, nitrogen reserves (N), total carbon (C), C/N ratio, cation exchange capacity (CEC), and macronutrient concentrations in soils under Pinus montezumae Lamb infested with Dendroctonus spp. and under healthy trees (same specie), as a control. The trees were grouped into three categories, according to the number of Dendroctonus resin’s lumps they presented. The functional diversity of soil bacteria was evaluated with Shannon-Weiner index. Significant differences were found in the contents of Ca, ammonium (NH4), and iron (Fe), they decrease while the frequency of lumps increases. The functional diversity of soil bacteria was higher in soils under asymptomatic pines. Taken together, our results show that Dendroctonus may be related to biological processes instead of chemical soil variables.

The metabolic and genetic diversity of soil bacterial communities depends on the soil management system and C/N dynamics: The case of sustainable and conventional olive groves

Under Mediterranean type climates, a sustainable soil management aimed at increasing soil organic carbon and microbiological diversity is of key importance. The aim of this study was to characterize and compare soils from a mature Mediterranean olive (Olea europaea L.) orchard subjected to two different soil management systems (sustainable, Smng, and conventional, Cmng) for 18 years. Composite soil samples were analyzed qualitatively (pedological determinations) and quantitatively (soil C, N and pH). Bacterial metabolic activity and diversity were evaluated spectrophometrically by the Biolog® assay, while 16S-based metagenomics analysis was used to analyse the abundance of N-cycling bacteria. From the general analysis of the data obtained by the study of soil profiles and litter, C and N dynamics, and the genetic and functional diversity of soil bacteria, it emerged that the Smng system caused an improvement in soil organic matter in the topsoil layers, compared to the Cmng system, with consequent increases in the abundance of soil N-cycling bacteria but without affecting the indices related to total bacterial metabolic activity and diversity. The results obtained could promote the development of new approaches for optimizing soil carbon cycling, managing nutrient transport, and sustaining and improving olive yield and quality.

Pseudomonas diversity in western Algeria: role in the stimulation of bean germination and common bean blight biocontrol

The aim of this work was to determine the functional diversity of soil bacteria belonging to the Pseudomonas genus, to study their effects on bean (Phaseollus vulgaris L) seed germination and their biocontrol potential of common bean blight. Bacteria were isolated and identified based on physiological and biochemical characters and BOX-PCR. Followed by qualitative and/or quantitative analysis of their secondary metabolites. 50 soil bacteria were affected to the two groups of fluorescent (72%) and non-fluorescent Pseudomonads (28%). The UPGMA (Unweighted Pair Group Method with Arithmetic Mean) showed five phenons of carbon sources assimilation; at the time that BOX-PCR profiling resulted in five clusters characterized by 29 different haplotypes. (66%) isolates induced phosphate solubilization; (24%) were HCN producers, (21%) showed IAA production and all isolates had produced siderophores. In vitro antibacterial activity against Xapf showed 26.67 and 24 mm of inhibition zone using the two isolates P. grimontii P25 and P. cepatia P7, respectively. Similarly, the same isolates significantly reduced Xapf-bean common blight intensity, while their co-inoculation was less effective. The isolate P. cepatia P7 was highly effective on seed germination and root growth properties, then P. grimontii P25. Thus, the selected isolates could play a crucial bean growth promotion and bean common blight biocontrol as alternative to chemicals for crop yield enhancement.

The Effects of Heavy Metals and Total Petroleum Hydrocarbons on Soil Bacterial Activity and Functional Diversity in the Upper Silesia Industrial Region (Poland).

Various inorganic and organic pollutants in industrial soils may adversely affect soil microorganisms and terrestrial ecosystem functioning. The aim of the study was to explore the relationship between the microbial activity, microbial biomass, and functional diversity of soil bacteria and the metals and total petroleum hydrocarbons (TPHs) in the Upper Silesian Industrial Region (Poland). We collected soil samples in pine-dominated forest stands and analyzed them according to a range of soil physicochemical properties, including metal content (cadmium, lead, and zinc) and TPH content. Metal concentrations were normalized to their toxicity to soil microorganisms and integrated in a toxicity index (TI). Soil microbial activity measured as soil respiration rate, microbial biomass measured as substrate-induced respiration rate, and the bacterial catabolic activity (area under the curve, AUC) assessed using Biolog® ECO plates were negatively related to TPH pollution as shown in multiple regressions. The canonical correspondence analysis (CCA) showed that both TPH and TI affected the community-level physiological profiles (CLPPs) of soil bacteria and the pollutants’ effects were much stronger than the effects of other soil properties, including nutrient content.Electronic supplementary materialThe online version of this article (doi:10.1007/s11270-016-2966-0) contains supplementary material, which is available to authorized users.

Covariation of soil bacteria functional diversity and vegetation diversity along an altitudinal climatic gradient in the Western Carpathians

The belowground microbiota are directly affected by vegetation via resource inputs and indirectly affected through the effects on physico-chemical soil properties. This study examines the relationship between vascular plant community diversity and the functional diversity of soil bacteria. The total vascular plant diversity of trees, shrubs and forest floor vegetation was investigated along an altitudinal climatic gradient in the Polish Carpathians. Soil (upper 10 cm) was collected in forest stands at three elevations (600, 900, and 1200 m a.s.l.) on five separate mountain slopes (treated as independent replicates). The overall microbial activity was determined by the soil respiration rate, whereas the bacterial catabolic activity and functional diversity (H′bact) was determined using Biolog® ECO plates. The vegetation diversity (H′plant) decreased with elevation. The organic matter content, water holding capacity and dissolved organic nitrogen differed significantly between elevations and were highest for stands at 1200 m a.s.l. Soil physico-chemical characteristics varied widely between sites and only showed an effect on the bacterial catabolic activity. Within microbial indices, only H′bact was correlated with elevation (p < 0.03). Both bacterial catabolic activity and functional diversity were positively correlated with H′plant (p < 0.005 and p < 0.02, respectively). Among the six chemical substrate groups on the Biolog® ECO plates, the most variable chemical substrate group utilised by soil bacteria were amines; their utilisation was highest for soil bacteria originated from 600 m a.s.l. and lowest for bacteria from 1200 m a.s.l. Our results underline the close associations between above- and belowground biological diversity in forest ecosystems, which can emerge as a result of carbon and nitrogen cycling.

Relating soil microbial properties to yields of no-till canola on the Canadian prairies

Soil microorganisms mediate many important biological processes for sustainable agriculture. However, correlations between soil microbial properties and crop productivity cannot always be demonstrated. We collected soil microbial data from a canola (Brassica napus L.) study that was conducted at seven sites on the Canadian prairies about agricultural practices focused on increasing canola yields. The treatments consisted of two canola seeding rates (75 or 150seedsm−2), two nitrogen rates (1× and 1.5× soil test recommendation) and three nitrogen form–fungicide (prothioconazole) combinations (uncoated urea, no fungicide; uncoated urea+fungicide; and 50% polymer-coated urea+fungicide) in a 2×2×3 factorial arrangement. Microbial biomass C (MBC), β-glucosidase enzyme activity and functional bacterial diversity (based on C substrate utilization patterns) were determined in canola rhizosphere and in bulk soil and related to canola yields. The effects of seeding rate, nitrogen (N) rate and N form on soil microbial biomass, enzyme activity or bacterial functional diversity were usually not statistically significant. In the few cases where significance occurred, doubling the seeding rate from 75 to 150seedsm−2 usually increased these microbial properties in canola rhizosphere or bulk soil. Increasing N rate to 1.5× the recommended rate had mostly positive effects in canola rhizosphere and negative effects in bulk soil. The effects of N form (including addition of fungicide) were inconsistent. Soil MBC and β-glucosidase enzyme activity correlated positively with canola grain yield at the five sites where yields were <4000kgha−1 (r=0.51** to 0.76**), but no or weak negative correlations were observed at the two sites with yields >4000kgha−1. The functional diversity of soil bacteria was not or was weakly negatively correlated with grain yields. Some of these relationships appeared to be influenced by canola root maggot damage because root damage was usually negatively correlated with the soil microbial characteristics, but the correlations were too weak to be relevant. These results suggest underground feedback interactions between crops and soil microbes, i.e., crop/soil management practices that enhance crop growth also enhance soil microbial communities and their activities, and vice versa.

Rapid Impact of Phenanthrene and Arsenic on Bacterial Community Structure and Activities in Sand Batches

The impact of both organic and inorganic pollution on the structure of soil microbial communities is poorly documented. A short-time batch experiment (6days) was conducted to study the impact of both types of pollutants on the taxonomic, metabolic and functional diversity of soil bacteria. For this purpose sand spiked with phenanthrene (500mgkg(-1) sand) or arsenic (arsenite 0.66mM and arsenate 12.5mM) was supplemented with artificial root exudates and was inoculated with bacteria originated from an aged PAH and heavy-metal-polluted soil. The bacterial community was characterised using bacterial strain isolation, TTGE fingerprinting and proteomics. Without pollutant, or with phenanthrene or arsenic, there were no significant differences in the abundance of bacteria and the communities were dominated by Pseudomonas and Paenibacillus genera. However, at the concentrations used, both phenanthrene or arsenic were toxic as shown by the decrease in mineralisation activities. Using community-level physiological profiles (Biolog Ecoplates™) or differential proteomics, we observed that the pollutants had an impact on the community physiology, in particular phenanthrene induced a general cellular stress response with changes in the central metabolism and membrane protein synthesis. Real-time PCR quantification of functional genes and transcripts revealed that arsenic induced the transcription of functional arsenic resistance and speciation genes (arsB, ACR3 and aioA), while no transcription of PAH-degradation genes (PAH-dioxygenase and catechol-dioxygenase) was detected with phenanthrene. Altogether, in our tested conditions, pollutants do not have a major effect on community abundance or taxonomic composition but rather have an impact on metabolic and functional bacterial properties.

Soil microbial response to nitrogen fertilizer and tillage in barley and corn

Cereal crops usually take up less than 50% of the N fertilizer applied. We hypothesized that, depending on application rate, the inorganic N in the soil could affect soil organisms. We investigated the effect of N applied to barley ( Hordeum vulgare L.) at soil-test recommended rates (50–80 kg ha −1) in 2004–2006 in a Black Chernozem, and to corn ( Zea mays L.) at recommended (80 kg ha −1) and higher (160 kg ha −1) N rates under no till (NT) and conventional tillage (CT) in 2004 and 2006 in an Orthic Gleysol, on soil microbial properties. Rhizosphere and bulk soil samples (0–7.5 cm soil depth) taken at flagleaf stage of barley growth and tasselling stage of corn growth were analysed for microbial biomass C (MBC), bacterial functional diversity and community-level physiological profiles (CLPPs). In barley, N increased MBC by 39% in bulk soil in one year. In corn, the response of MBC to N rate was quadratic, peaking at 80 kg N ha −1. The functional diversity of soil bacteria in the corn trial was not reduced even at the highest N rate. No-till in corn increased MBC by 30–102%, and also tended to increase bacterial functional diversity. The tillage effect was detectable in CLPPs although year-to-year differences were more prominent. Therefore, N applied at agronomically recommended rates either did not affect MBC and bacterial diversity or increased these microbial characteristics; N applied at higher rates reduced MBC. These results from two soil types, crops and climatic regions support our hypothesis that non-target effects of N fertilizer depend on the application rate. Soil testing to apply recommended amounts of fertilizer would reduce non-target fertilizer effects.

Soil microbial response to herbicides applied to glyphosate-resistant canola

Adoption of glyphosate-resistant canola ( Brassica napus L.) has increased glyphosate applications to this crop, and concerns have been raised about unintended consequences of these multiple applications. A field trial was conducted to evaluate the effects of pre-seed and in-crop glyphosate and alternative herbicides on soil microbial community functional structure, diversity and biomass. Pre-seed treatments were 2,4- D, glyphosate and 2,4- D + glyphosate, and in-crop treatments were glyphosate applied once, glyphosate applied twice, ethalfluralin, ethalfluralin + sethoxydim + ethametsulfuron + clopyralid, and sethoxydim + ethametsulfuron. Rhizosphere and bulk soil was collected at flowering stage of canola and analyzed for bacterial community-level substrate utilization patterns and microbial biomass C (MBC). Where differences were significant, pre-seed application of both 2,4-D and glyphosate altered the functional structure and reduced the functional diversity of soil bacteria, but increased MBC. These effects were not necessarily concurrent. The reduction in functional diversity was due to reduction in evenness, which means that the soil where both pre-seed herbicides had been applied was dominated by only few functional groups. In 1 year, two in-crop applications of glyphosate also reduced the functional diversity of soil bacteria when applied after pre-seed 2,4-D, as did in-crop sethoxydim + ethametsulfuron following pre-seed glyphosate. Even though significant differences between herbicides were fewer than non-significant differences, i.e., there were no changes in soil microbial community structure, diversity or biomass in response to glyphosate or alternative herbicides applied to glyphosate-resistant canola in most cases, the observed changes in soil microbial communities could affect soil food webs and biological processes.

Functional diversity of soil bacteria as affected by management practices and phenological stage of Phaseolus vulgaris

This study focused on the effect of management regime and crop developmental stage on soil bacterial functional diversity by using GN Biolog plates. The fields examined were: a grazed grassland (Gr), 2 conventional cultivations differing in the amount and the quality of chemical inputs (C-1 and C-2) and 5 fields cultivated organically for 14, 10, 8, 5 and 2 years respectively. All agricultural lands were cultivated with Phaseolus vulgaris L. Sampling was conducted at seedling emergence, in the mid-growth and after harvest. Low values of diversity were recorded in grassland and conventional fields with the lowest ones in C-2 field. In organic fields, diversity was not related to the age of organic cultivation. However, despite diversity similarities a gradual evolution in community functionality was recorded that parallel changes in the rate of substrate consumption. Increased catabolic activity and diversity followed by changes in the composition of consumed wells occurred in the middle of the phaseolus growth period. Finally, the effect on catabolic profiles of crop developmental stage in conjunction with seasonally varying abiotic conditions was of greater magnitude than that of management regime. The temporal changes in bacterial functionality were totally absent at the C-2 field.

Soil microbial biomass, functional diversity and enzyme activity in glyphosate-resistant wheat–canola rotations under low-disturbance direct seeding and conventional tillage

As glyphosate-resistant (GR) crops are becoming common in agro-ecosystems, their effects on non-target soil organisms need to be monitored. We evaluated soil microbial biomass C (MBC), bacterial functional diversity and community structure, and dehydrogenase enzyme activity in a field experiment conducted at six sites on the Canadian prairies. Treatments consisted of a factorial arrangement of three GR wheat and GR canola crop frequencies and two tillage systems. GR crop frequencies were arranged in 4-yr wheat-canola-wheat-pea rotations, with GR wheat and GR canola in zero of four, two of four, or three of four possible GR crop frequencies. The two tillage systems were either low soil-disturbance direct-seeding (LDS) or conventional tillage (CT). MBC increased with increasing frequency of GR crops in two of 20 site-years in the rhizosphere, and had no effects in bulk soil. Depending on tillage, GR crop frequency also affected the functional diversity of rhizosphere soil bacteria in only two of 20 site-years, and had no effects in bulk soil. Shifts in the structures of bacterial communities related to GR crop frequency were detected, but they were few and inconsistent. In three of 22 cases (10 in rhizosphere+12 in bulk soil), the activity of dehydrogenase enzyme decreased with increasing frequency GR crops in both the rhizosphere and bulk soil. In five of 20 site-years, soil MBC in the rhizosphere was greater under CT than under LDS, regardless of GR crop frequency. In bulk soil, tillage affected soil MBC in five site-years, three of which had greater MBC under CT than LDS, and vice versa in the other two. Tillage affected the functional diversity of soil bacteria in the rhizosphere in three site-years, but the effects were not consistent. Similar inconsistent tillage-related patterns were observed in the community structures of bacteria. There were no tillage effects on bacterial diversity in bulk soil. Dehydrogenase enzyme activity was greater under LDS than under CT in three of four cases in which tillage had significant effects. Overall, GR crop frequency effects on soil microorganisms were minor and inconsistent over a wide range of growing conditions and crop management.

Soil microbial biomass, functional diversity and crop yields following application of cattle manure, hog manure and inorganic fertilizers

Soil biological properties can be significantly impacted by land management. Cattle manure, hog manure or inorganic fertilizers were applied annually or triennially in field trials conducted at two sites over 3 yr. A control treatment without manure or fertilizer was also included. Canola (Brassica napus) was grown in year 1, hulless barley (Hordeum vulgare) in year 2, and wheat (Triticum aestivum) in year 3. Where effects were significant, cattle manure increased soil microbial biomass C (MBC) by 26% to three-fold, hog manure by 31% to two-fold, and inorganic fertilizers reduced MBC by 20–64%. Similar effects, except the reduction by inorganic fertilizers, were observed for functional diversity of soil bacteria (Shannon index, H′ ). At one site, where crop yields were recorded for 3 yr, hog manure produced greater grain yields (75% increase over the control) than the rest of the treatments (49% increase by cattle manure) in year 1, but cattle manure out-yielded other treatments thereafter, when it increased yields by 25–50%. Cattle manure out-yielded other treatments even when nutrient uptake from inorganic fertilizers was the highest, implying that other factors also influenced crop yields. At the other site, crop yields were recorded only in year 1, and all soil amendments increased canola yields about three-fold relative to the control. Frequency of application usually had no effects on MBC or H′, but the triennial application rate of inorganic fertilizers or hog manure produced lower crop yields than annual applications in year 1. Key words: Functional diversity, Gray Luvisol, manure quality, NPK fertilizers, soil microbial communities

The effects of large- and small-scale differences in soil temperature and moisture on bacterial functional diversity and the community of bacterivorous nematodes

This paper describes the effects of large-scale seasonal fluctuations as well as experimentally induced small-scale variations of soil temperature and moisture on the community of bacterivorous nematodes and the activity of soil bacteria from a Greek Mediterranean grassland. Our experiment spanned a 6-month period (July–December 1996), during which artificially created changes in temperature (1.4 °C) and moisture content of the soil (2.3%) were superimposed on seasonal variations of these variables. Functional diversity of soil bacteria was assessed using Biolog GN-plates. Bacterial diversity, richness and evenness as well as the mean oxidation of almost all Biolog substrate groups, were affected significantly by the seasonal fluctuations of soil temperature and moisture, and declined linearly from July to December. The substrates responsible for the differences in monthly soil samples were mainly carbohydrates and carboxylic acids. The small-scale experimental changes in temperature and moisture affected oxidation of only four out of the eight substrate groups. The effect of seasonality was also obvious on the diversity, evenness, richness and total density of soil bacterivorous nematodes, which exhibited higher values during the period September–October. The effect of experimental temperature and moisture modifications varied between the different nematode taxa. Acrobeles, Chiloplacus and Cephalobus responded significantly to small-scale temperature changes, while the responses of the other taxa, if any, were more complicated, depending on the interactive effect of both soil temperature and moisture. In any case, the experimental modifications of moisture alone did not induce significant changes in the structure of the nematode community. After comparing the community parameters of bacteria and bacterivorous nematodes, we conclude that there was no synchronised response between nematodes and their food resources.