Abundance Of Microbial Functional Groups Research Articles

Climatic Variability Determines the Biological Diversity and Function of a Mixed Forest in Northeastern China at the Local-Scale

The adaptation to climatic variability and spatiotemporal distinctions in floristic and microbial assembly is important in forest ecology, especially in the context of biological diversity and functional traits. We investigated climatic variables, plant traits, edaphic properties, and microbial dimensions from various plots with an elevation gradient in a broad-leaved-Korean pine mixed forest. With increasing elevation, isothermality significantly increased; however, temperature and precipitation seasonality, as well as the mean temperature of the warmest quarter, significantly declined. Furthermore, high elevation sites were characterized by increased stand basal areas (Ba) and ectomycorrhizal (EM) tree abundance but featured decreases in the abundance of arbuscular mycorrhizal (AM) trees and the values of community-weighted mean (CWM) foliar traits (e.g., leaf area, leaf nitrogen content and leaf phosphorus content). Moreover, soil nutrient status, fungal and bacterial diversity indices, fungal saprotrophs, and bacterial function groups related to nitrite oxidation, ammonia oxidation, and nitrate denitrification were all negatively correlated to the elevation increment. In contrast, high elevation sites were characterized by enhanced EM growth and bacterial nitrogen fixation groups. Correlation analysis showed that the microbial diversity and relative abundances of microbial functional groups in soil were significantly influenced by climatic variability, CWM foliar traits and soil nutrient status. These findings demonstrate that the forces driving biological processes along climatic gradients are predictably in tandem with, but related to different extents, to the spatial compartmentalization of climatic variability in forest ecosystems at local scales.

Diversity and Abundance of Microbial Communities in UASB Reactors during Methane Production from Hydrolyzed Wheat Straw and Lucerne.

The use of straw for biofuel production is encouraged by the European Union. A previous study showed the feasibility of producing biomethane in upflow anaerobic sludge blanket (UASB) reactors using hydrolyzed, steam-pretreated wheat straw, before and after dark fermentation with Caldicellulosiruptor saccharolyticus, and lucerne. This study provides information on overall microbial community development in those UASB processes and changes related to acidification. The bacterial and archaeal community in granular samples was analyzed using high-throughput amplicon sequencing. Anaerobic digestion model no. 1 (ADM1) was used to predict the abundance of microbial functional groups. The sequencing results showed decreased richness and diversity in the microbial community, and decreased relative abundance of bacteria in relation to archaea, after process acidification. Canonical correspondence analysis showed significant negative correlations between the concentration of organic acids and three phyla, and positive correlations with seven phyla. Organic loading rate and total COD fed also showed significant correlations with microbial community structure, which changed over time. ADM1 predicted a decrease in acetate degraders after a decrease to pH ≤ 6.5. Acidification had a sustained effect on the microbial community and process performance.

Land use, soil and litter chemistry drive bacterial community structures in samples of the rainforest and Cerrado (Brazilian Savannah) biomes in Southern Amazonia

Southern Amazonia harbors the largest agricultural frontier worldwide, where native vegetation has been converted to agriculture. Land use change in this region compromises deforestation as well as changes in agricultural management intensity (e.g. liming, fertilization, and number of crops) that shapes plant cover and soil chemistry. Our objective was to investigate the effects of these changes on soil bacterial community structure (i.e. community composition based on T-RFLP profiles of 16S rRNA and abundance of functional groups related to C and N cycling). Two representative agricultural regions within the biomes rainforest and Cerrado were chosen, each spanning land uses from native vegetation to pasture and soybean fields, and three replicated sites sampled for each land use type/region. Soil chemical alterations concurrent with land use changes to agriculture included increases in soil pH, Ca, Mg, P, K, and N concentrations, and easily decomposable litter. These alterations influenced bacterial community structure by changing both, community composition and functional gene abundance, findings supported by redundancy analysis and principal components analysis. Confirming one of our working hypotheses, based on the 16S rRNA gene, bacterial richness did not decrease from pristine vegetation to agricultural uses, but its composition shifted with land use change. In addition, a change in the abundance of microbial functional groups related to the production of the greenhouse gases N2O (denitrifiers, nosZ), and CH4 (methanogens, mcrA and methanotrophs, pmoA) reflected the influence of land use change in samples from both biomes. In accordance with our second hypothesis, the management intensive soybean soils exhibited the most distinct chemical (higher pH and nutrient levels) and microbiological profiles, including a significant decrease of the functional genes tested. In conclusion, our results identify land use intensity (namely its alterations in soil pH, C, litter degradability, pesticides and nutrient levels) as the driver for soil bacterial community structure (T-RFLP composition of 16S rRNA genes and functional gene abundance) in the studied samples. These formed a gradient of land use change consequences from native vegetation, to pasture and then to the soybean areas, which presented the most distinct chemical and bacterial profiles.

Microbial community composition explains soil respiration responses to changing carbon inputs along an Andes-to-Amazon elevation gradient.

1. The Andes are predicted to warm by 3–5 °C this century with the potential to alter the processes regulating carbon (C) cycling in these tropical forest soils. This rapid warming is expected to stimulate soil microbial respiration and change plant species distributions, thereby affecting the quantity and quality of C inputs to the soil and influencing the quantity of soil-derived CO2 released to the atmosphere.2. We studied tropical lowland, premontane and montane forest soils taken from along a 3200-m elevation gradient located in south-east Andean Peru. We determined how soil microbial communities and abiotic soil properties differed with elevation. We then examined how these differences in microbial composition and soil abiotic properties affected soil C-cycling processes, by amending soils with C substrates varying in complexity and measuring soil heterotrophic respiration (RH).3. Our results show that there were consistent patterns of change in soil biotic and abiotic properties with elevation. Microbial biomass and the abundance of fungi relative to bacteria increased significantly with elevation, and these differences in microbial community composition were strongly correlated with greater soil C content and C:N (nitrogen) ratios. We also found that RH increased with added C substrate quality and quantity and was positively related to microbial biomass and fungal abundance.4. Statistical modelling revealed that RH responses to changing C inputs were best predicted by soil pH and microbial community composition, with the abundance of fungi relative to bacteria, and abundance of gram-positive relative to gram-negative bacteria explaining much of the model variance.5. Synthesis. Our results show that the relative abundance of microbial functional groups is an important determinant of RH responses to changing C inputs along an extensive tropical elevation gradient in Andean Peru. Although we do not make an experimental test of the effects of climate change on soil, these results challenge the assumption that different soil microbial communities will be ‘functionally equivalent’ as climate change progresses, and they emphasize the need for better ecological metrics of soil microbial communities to help predict C cycle responses to climate change in tropical biomes.

Effects of grazing on N2O production potential and abundance of nitrifying and denitrifying microbial communities in meadow-steppe grassland in northern China

PurposeThe aim of this study was to investigate the effects of cattle grazing on the nitrous oxide (N2O) production potential from meadow-steppe grassland soil in northern China, and the relationship between cattle grazing and the abundance of different functional microbial genes for potential of N2O emissions. Materials and methodsWe collected soil samples at a depth of 0–20 cm over six times during two plant growing seasons in 2011 and 2012 on a native Leymus chinensis grassland. At each of the six sampling occasions, soil samples were taken from three pairs of the cattle grazed vs. ungrazed plots. We then determined (1) the soil moisture, pH, total carbon and nitrogen, and mineral N (NH4+ and NO3−) content, (2) the potential rates of N2O production from nitrification (NN2O) and from denitrification (DN2O and DN2) using the acetylene inhibition method, and (3) the abundance of the amoA (ammonia monooxygenase) gene of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), the narG (nitrate reductase) gene and nosZ (nitrous oxide reductase) gene using quantitative real-time PCR (qPCR). The relationship among the changes in the N2O production potential rates, the abundance of microbial functional groups and the soil environment was analyzed using mix effects modeling and structural equation modeling. Results and discussionThe AOA, AOB, narG, nosZ genes and the potential N2O production rate all varied significantly with the season (P < 0.01). Grazing induced an overall reduction in soil moisture (P < 0.05) and soil total N in 2012 (P < 0.05), and a significant increase in the abundance of AOB genes (P < 0.05); but no significant difference between grazing treatments was found on the abundance of AOA, narG and nosZ genes, or on the NN2O and DN2O.Approximately 80% of the variation in NN2O could be explained by the abundance of AOA and AOB genes (P < 0.0001), which in turn was explained by soil NH4+ content and soil moisture; The abundance of narG gene, along with total C, NO3− content and soil moisture, explained 87% of variation in the DN2 (P < 0.0001). The abundance of narG gene was related to the production of N gases from denitrification (DN2O+N2), but not the DN2O. Soil moisture was the best predictor for DN2O. ConclusionsThe abundance of amoA and narG genes are good indicators for the potential nitrification and denitrification rates in the meadow steppe grassland. Soil moisture is the most important factor controlling the N2O emission potential in the meadow-steppe grassland. The grassland soils protected from animal grazing or that under a moderate grazing for five years did not show a significant difference in potential N2O emissions. Our results suggest that grazing induced grassland degradation may not necessarily be associated with a reduction in N2O emissions as reported in other semiarid grasslands in a more arid environment.

Impact of future climatic conditions on the potential for soil organic matter priming

Terrestrial carbon (C) storage and turnover are of major interest under changing climatic conditions. We present a laboratory microcosm study investigating the effects of anticipated climatic conditions on the soil microbial community and related changes in soil organic matter (SOM) decomposition. Soil samples were taken from a heath-land after six years of exposure to elevated carbon dioxide (eCO2) in combination with summer drought (D) and increased temperature (T). Soil C-dynamics were investigated in soils from: (i) ambient, (ii) eCO2, and (iii) plots exposed to the combination of factors simulating future climatic conditions (TDeCO2) that simulate conditions predicted for Denmark in 2075. 13C enriched glucose (3 atom% excess) was added to soil microcosms, soil CO2 efflux was measured over a period of two weeks and separated into glucose- and SOM-derived C. Microbial biomass was measured using chloroform fumigation extraction, and compound-specific phospholipid fatty acid analysis was used to determine microbial community composition and substrate use. We observed that glucose additions induced SOM priming in ambient and eCO2 treated soils, but not in soil exposed to future climatic conditions. Climate treatments and glucose additions did not affect relative abundances of microbial functional groups but the fate of glucose through the microbial community was changed by climate treatments as revealed by the incorporation of 13C in PLFAs. Soil treated with eCO2 showed a high flow of glucose through gram-positive bacteria whereas in ambient and future soils utilization of glucose by actinomycetes and fungi (putative SOM-decomposers) was greater. Our results suggest that individual climate change factors may influence pathways of C-flux through microbial communities and therefore affect soil processes; these factors may counterbalance each other and maintain ecosystem stability. This highlights the importance of studying climate change factors in combination to fully assess consequences of environmental change on plant–soil systems.

Microbial Dynamics and Fertility Characteristics in Compost from Different Waste and Maturation Processes

We evaluated the abundance of microbial functional groups involved in compost fertility, and the chemical pa- rameters of maturity and quality most commonly analyzed in compost products. We employed compost produced using the same hydrolytic stage and two maturation processes (with and without earthworms) and with different organic wastes. Our aim was to propose a valid tool for measuring the quality standards of compost fertility from a microbial perspective. The products obtained from both maturation processes were highly variable in their chemical and biological composition (without following a general pattern). Because the results are so heterogeneous, proposing a microbial population as uni- versal indicator of the degree of compost fertility is very difficult. However, the microbial community structure might be used as a maturity index, because the products that best fulfilled the chemical stability parameters were those with lowest number of populations in its community.

Spatiotemporal heterogeneity of soil fertility in the Central Monte desert (Argentina)

In arid environments, soil fertility exhibits a high degree of spatial and temporal heterogeneity, which results from high climatic variability seasonally and heterogeneous plant distribution. However, because most desert areas have been altered by human activities, heterogeneous fertility would originate from grazing or logging activities. We evaluated spatial and temporal heterogeneity of soil fertility in cattle-excluded sites under and outside woody plant cover ( Prosopis flexuosa and Larrea divaricata), and in sites disturbed by tree removal during wet and dry season in Ñacuñán Biosphere Reserve (Central Monte desert of Argentina). Soil organic matter, fulvic acids, bioavailable organic matter, and nitrate were lower outside plant canopy (8.9 mg g −1, 0.03 mg g −1, 8.2 mg g −1, and 4.17 mg kg −1, respectively). Total N, humic acids, and abundance of microbial functional groups did not show differences among sites. Most parameters differed between seasons, tending to be higher in the wet season. Overall soils of Ñacuñán Reserve are characterized by: a) more homogenous spatial pattern than expected from woody plant presence; b) very heterogeneous temporal pattern; and c) after two years, tree removal does not seem to induce infertile soil formation.

A comparison of nutrient sources of the epiphyte Tillandsia capillaris attached to trees and cables in Cordoba, Argentina

Tillandsia capillaris Ruiz and Pav is an atmospheric epiphytic bromeliad able to grow attached to both trees and power lines in the arid–semiarid regions. We evaluated the influence of support type on nutrient sources of atmospheric bromeliads through of: a) quantity and chemical composition of material retained in the leaf surface (MRL) (dry weight, pH, nitrate, ammonium, phosphate and sulfate contents); b) chemical composition of plant tissues (nitrogen, phosphorous, carbon and chlorophyll contents); and c) nitrogenase activity and abundance of microbial functional groups involved in N cycling in leaf surface (phyllosphere). In the cable situation, MRL was lighter, more acidic, with a higher nitrate and sulfate content and lower phosphate content than in the tree situation. T. capillaris plant tissues on trees had lower N (89%) and higher C (6%) content than plants on cables. Phyllosphere micro-organisms' abundance and nitrogenase activity were similar in both situations. Our results indicate that T. capillaris has similar nutrient sources in both supports, and in consequence atmospheric bromeliads do not need plant host for their nutrition.