Differences In Microbial Activity Research Articles

Remote sensing of cover crop legacies on main crop N‐uptake dynamics

AbstractGrowing cover crops promotes soil health as they retain nutrients during autumn/winter and provide organic matter to the soil biota, which in turn supplies nutrients to the main crop upon mineralisation in spring. Different cover crops have varying impacts on soil biology and nutrient dynamics due to the quantity and quality of plant material returned to the soil. To understand these effects, high‐resolution data on crop responses is required. In this study, remote sensing was used to provide such data. The temporal dynamics of soil nitrogen (N) availability and N uptake in barley were studied in response to different cover crop monocultures and mixtures. This was achieved using high‐resolution multispectral images of the main crop acquired from an unmanned aerial vehicle. Alongside this, in‐situ collected plant and soil parameters were used in this 5‐year cover crop field experiment. The results showed that cover crop legacies significantly affected barley N uptake, biomass, and canopy N content. In early June, at peak canopy N, the highest values were observed in barley grown after vetch‐radish or oat‐radish mixtures (84 kg N/ha) and the lowest in barley grown after fallow (63 kg N) or oat (53 kg N/ha on 23rd of June). At the start of the barley growing season, soil microbial biomass was not significantly affected by the cover crop legacies. However, differential N mineralisation between cover crop legacies can be attributed to differences in microbial activity associated with cover crop quantity and quality. This research demonstrates the potential of remote sensing to monitor and understand temporal and spatial variation of crop canopy N in response to cover crop N mineralisation by the soil biota which is an important component of soil health. This approach can contribute to more efficient N use by enabling fine‐tuning of the type, quantity, timing, and location of fertilisation.

Microbial response to Nature-Based Solutions in urban soils: A comprehensive analysis using Biolog® EcoPlates™

The study presents a comprehensive examination of changes in soil microbial functional diversity (hereafter called microbial activity) following the implementation of Nature-Based Solutions (NBS) in urban areas. Utilizing the Biolog® EcoPlates™ technique, the study explored variations in microbial diversity in urban soil under NBSs implementation across timespan of two years.Significant differences in microbial activity were observed between control location and those with NBS implementations, with seasonal variations playing a crucial role. NBS positively impacted soil microbial activity especially at two locations: infiltration basin and wild flower meadow showing the most substantial increase after NBS implementation. The study links rainfall levels to microbial functional diversity, highlighting the influence of climatic conditions on soil microbiome. The research investigates also the utilization of different carbon sources by soil microorganisms, shedding light on the specificity of substrate utilization across seasons and locations. The results demonstrate that NBSs implementations lead to changes in substrate utilization patterns, emphasizing the positive influence of NBS on soil microbial communities. Likewise, biodiversity indices, such as Shannon-Weaver diversity (H′), Shannon Evenness Index (E), and substrate richness index (S), exhibit significant variations in response to NBS. Notably, NBS implementation positively impacted H′ and E indexes, especially in infiltration basin and wild flower meadow, underlining the benefits of NBS for enhancing microbial diversity.The obtained results demonstrated valuable insight into the dynamic interactions between NBS implementation and soil microbial activity. The findings underscore the potential of NBS to positively influence soil microbial diversity in urban environments, contributing to urban sustainability and soil health. The study emphasizes the importance of monitoring soil microbial activity to assess the effectiveness of NBS interventions and guides sustainable urban development practices.

The effect of a multi-carbohydrase enzyme and yeast-derived product on intestinal microbiome structure, activity, and gut function of turkeys

The effect of a multi-carbohydrase (E) and its combination with an enzymatically modified yeast cell wall (Y) on the ileal and cecal microbiota and on gut function of turkeys was studied. The experimental diets, including the control (C), C + E, and C + E + Y, were fed to seven replicate pens of four birds from 22 to 56 days of age. The addition of E + Y resulted in a significant decrease in the relative abundance of Firmicutes and a significant increase of Actinobacteria in ileal digesta. A significant decrease in the abundance of Firmicutes was not followed by the abundance of Ruminococcaceae, one of the butyrate-producing bacteria. This coincided with a significantly increased concentration of butyrate in the ileal digesta and the proportion of butyrate within the total short-chain fatty acids (SCFA). As opposed to the ileum, the addition of E or E + Y did not affect the relative abundance of Firmicutes in ceca. The higher content of SCFA in the cecal digesta than in the ileum would reflect differences in microbial activities in both compartments, and possible increased SCFA absorption from the ileum. Overall, the positive effects of enzyme and yeast bioactive supplements on bacterial communities appeared to be more pronounced in the small intestine.

Functional significance of the leaf-cutting ant Atta cephalotes (Formicidae) in coffee plantations: An enemy or an ally?

Leaf-cutter ants are appreciated as ecosystem engineers. Conversely, under agricultural scenarios, they are considered serious pests. Coffee is one of the crops selectively foraged by this species either under traditional shading or unshaded intensified systems. Despite the economic importance of coffee in Neotropical regions, there are few observational field studies on the impact of leaf-cutter ants on coffee plantation soils and how impact may differ in response to shade management. Three hypotheses were tested in coffee plantations in presence of Atta cephalotes: (1) bioturbation activity by leaf-cutter ants depends on the soil properties, which in turn, are affected by agronomic management of the coffee plantations; (2) a relatively higher concentration of resources (i.e., coffee plants) results in greater leaf-cutter ant activity in unshaded plantations than in shaded plantations; and (3) the effect of ant defoliation on fruit production depends on the level of foliar damage. Ten active ant nests were selected from each management system in ten farm plots. Soil samples were collected from nests and from outside the nests (control), physical, chemical and biological properties were analysed, and leaf-cutter ant herbivory was also assessed. No significant differences in microbial activity, evaluated through respiration, were found between nest and control soils. Nest soils had higher and lower percentages of sand and silt, respectively, than the control soils. Nest soils contained significantly higher amounts of sulphur, regardless of shade management. A. cephalotes translocated mineral soils and improved water infiltration in nest soils. The herbivory index and proportion of damage were greater in unshaded coffee, although fruit production tended to increase, possibly due to a compensatory effect as coffee plants responded to low levels of foliar damage. Therefore, the first hypothesis was only partially supported since bioturbation depended on soil properties, and certain soil properties were affected by coffee management, while the second and third hypotheses were supported by the data, suggesting that leaf-cutter ants differentially affect coffee plantations based on their shade management and on the moment the coffee plants are affected. Our results form the basis for the development of future studies that evaluate production impacts and economic damage in coffee varieties by leaf-cutter ants. Depending on the ecological context of the agroecosystem and management practices used, leaf-cutter ants can have positive or negative impacts for coffee production.

Effects of soil microbial communities associated to different soil fertilization practices on tomato growth in intensive greenhouse agriculture

Intensive greenhouse vegetable production is one of the most important economic activities in south-east Spain. Agricultural intensification has limited the application of organic matter (OM) in favor of synthetic chemical fertilizers, leading to altered soil microbial communities and production loss. We addressed the effects of soil microbial communities on plant productivity depending on different soil management practices in greenhouse agriculture. Greenhouse managements were i) conventional (i.e., with addition of synthetic chemical fertilizers) without organic amendments (CM), ii) conventional with organic amendments (CMOM) and with addition of synthetic chemical fertilizers, and iii) organic management with annual organic amendments and with no synthetic chemical fertilizer addition (ORG). We extracted soil microbial communities from five greenhouses per management type, added these inocula to pots with sterile substrate (peat:sand), and seeded disinfected tomato seeds. Plants grew for 2 months without nutrient addition (only water irrigation). Immediately prior to the end of the study, we measured photosynthetic rate, plant growth, and leaf functional traits. At the end of study, pot substrates inoculated with i) ORG soil communities had higher bacterial abundance (qPCR) compared to microbial communities inoculated with CM extracts; and ii) prokaryotic communities of CM and CMOM substrates differed in composition. Besides, substrates inoculated with CM inocula were significantly associated with the presence of a potential fungal pathogen. Plants inoculated with extracts from organic greenhouses grew more and had a higher photosynthetic rate than plants receiving soil microbial extracts from greenhouses with conventional management. There were differences in the NO3−, total N and organic matter contents of substrates between treatments at the end of the study, but not at the beginning of the study, suggesting differences in microbial activity between treatments. Although substrate N content differences did not translate into differences in leaf N, leaf δ15N differed between treatments, indicating that the source of the soil microbial inocula influenced the N compound used by the tomato plants. Overall, this study suggested that soil microbial communities from organic greenhouses had a positive effect on crop productivity in intensive greenhouse agriculture.

Potential for suppression of Rhizoctonia root rot is influenced by nutrient (N and P) and carbon inputs in a highly calcareous coarse-textured topsoil

Bioassays were undertaken in a controlled environment to assess whether the potential for suppression of Rhizoctonia root rot of wheat, in a highly calcareous topsoil, was positively influenced by nutrient (nitrogen (N) or phosphorus (P)) addition and whether any disease suppression response to augmented nutrition was affected by the addition of carbon (C), either as a readily available C source (sucrose) or as wheat stubble. The soil was P deficient, which limited plant growth, populations of putatively beneficial soil microorganisms, and microbial activity and diversity. This ultimately reduced potential for suppression of Rhizoctonia solani AG8. Addition of fertiliser P to the soil increased R. solani AG8 DNA and percent root infection but not the effectiveness of the pathogen. A positive effect of P fertiliser on plant growth partially compensated for the negative effect of increased root infection. Addition of P increased DNA for Microbacterium spp. where labile C had been added and in the presence of plant roots. Stubble addition alone, after 6 weeks of incubation, increased DNA for Pantoea agglomerans, Trichoderma A and Microbacterium spp. although differences in microbial activity and diversity between stubble treatments were only detected after the bioassay had commenced and P was added. Fertiliser P addition to stubble-amended soil resulted in less Rhizoctonia infection compared with that in soil without P or stubble addition. Effectiveness of R. solani AG8 was decreased by 50% with stubble amendment. The application of N alone did not have a marked effect on plant growth or potential for suppression of Rhizoctonia root disease. Agronomic management practices that affect quantity and lability of C input to soil, when combined with strategic P fertiliser decisions, are likely to improve the potential for development of suppression of Rhizoctonia root rot disease in cereal crops on alkaline and highly calcareous soils.

Ammonia volatilization from composting with oxidized biochar

Animal manure, agricultural residues, and other sources of biomass can be diverted from the waste stream and composted into valuable fertilizer. However, composting often results in substantial N loss through NH3 gas volatilization. We investigated biochar's capacity to improve NH3 -N retention during composting of poultry manure and straw. After 7wk, total N loss from composting with unoxidized biochar was twofold and sixfold higher than N loss from composting with oxidized biochar and without biochar (307, 142, and 51mg N g-1 N in the initial compost feedstocks, respectively). When cumulative NH3 -N loss was calculated relative to CO2 -C loss to account for differences in microbial activity, NH3 -N/CO2 -C loss from compost with oxidized biochar was 55% lower than from compost with unoxidized biochar (82% lower based on mass balance). Oxidized biochar particles removed from compost after 7wk retained 16.0mg N g-1 biochar, compared with only 6.1mg N g-1 retained by unoxidized biochar, suggesting that N retention by biochar particles provides a mechanism for reduced NH3 -N loss. These data show that oxidized biochar enhanced microbial activity, doubled composting rate, and reduced NH3 -N loss compared with unoxidized biochar and that biochar's physiochemical characteristics modulate its performance in compost. In particular, the presence of oxidized surface functional groups, which can be increased artificially or through environmental weathering, appear to play an important role in key compost processes. This has implications for other natural and managed systems where pyrogenic organic matter may mediate biological activity and nutrient cycles.

Microbial activity and metamitron degrading microbial communities differ between soil and water-sediment systems

The herbicide metamitron is frequently detected in the environment, and its degradation in soil differs from that in aquatic sediments. In this study, we applied 13C6-metamitron to investigate the differences in microbial activity, metamitron mineralization and metamitron degrading microbial communities between soil and water-sediment systems. Metamitron increased soil respiration, whereas it suppressed respiration in the water-sediment system as compared to controls. Metamitron was mineralized two-fold faster in soil than in the water-sediment. Incorporation of 13C from 13C6-metamitron into Phospholipid fatty acids (PLFAs) was higher in soil than in sediment, suggesting higher activity of metamitron-degrading microorganisms in soil. During the accelerated mineralization of metamitron, biomarkers for Gram-negative, Gram-positive bacteria and actinobacteria dominated within the 13C-PLFAs in soil. Gram-negative bacteria dominated among the metamitron degraders in sediment throughout the incubation period. Actinobacteria, and actinobacteria and fungi were the main consumers of necromass of primary degraders in soil and water-sediment, respectively. This study clearly showed that microbial groups involved in metamitron degradation depend on the system (soil vs. water-sediment) and on time. It also indicated that the turnover of organic chemicals in complex environments is driven by different groups of synthropic degraders (primary degraders and necromass degraders) rather than by a single degrader.

Optimal influent N-to-P ratio for stable microalgal cultivation in water treatment and nutrient recovery

Species specific nitrogen-to-phosphorus molar ratio (NPR) has been suggested for green microalgae. Algae can store nitrogen and phosphorus, suggesting that the optimum feed concentration dynamically changes as function of the nutrient storage. We assessed the effect of varying influent NPR on microalgal cultivation in terms of microbial community stability, effluent quality and biokinetics. Mixed green microalgae (Chlorella sorokiniana and Scenedesmus sp.) and a monoculture of Chlorella sp. were cultivated in continuous laboratory-scale reactors treating used water. An innovative image analysis tool, developed in this study, was used to track microbial community changes. Diatoms proliferated as influent NPR decreased, and were outcompeted once cultivation conditions were restored to the optimal NPR range. Low NPR operation resulted in decrease in phosphorus removal, biomass concentration and effluent nitrogen concentration. ASM-A kinetic model simulation results agreed well with operational data in the absence of diatoms. The failure to predict operational data in the presence of diatoms suggest differences in microbial activity that can significantly influence nutrient recovery in photobioreactors (PBR). No contamination occurred during Chlorella sp. monoculture cultivation with varying NPRs. Low NPR operation resulted in decrease in biomass concentration, effluent nitrogen concentration and nitrogen quota. The ASM-A model was calibrated for the monoculture and the simulations could predict the experimental data in continuous operation using a single parameter subset, suggesting stable biokinetics under the different NPR conditions. Results show that controlling the influent NPR is effective to maintain the algal community composition in PBR, thereby ensuring effective nutrients uptake.

Plant detritus origin and microbial–detritivore interactions affect leaf litter breakdown in a Central Apennine (Italy) cold spring

The decomposition of dead organic matter is a key process for the metabolism and functioning of lotic ecosystems. Particulate organic matter from fallen leaves is the main source of energy input also in forested springs. However, detritus processing in spring habitats has been rarely investigated. The present paper is aimed to assess, for the first time, the influence of detritus origin on leaf litter breakdown in a hydrologically, thermally and chemically stable cold spring and to evaluate the relative contribution of microorganisms and invertebrate detritivores to the decomposition process. For this purpose, we used leaves of the native black poplar (Populus nigra) and the invasive common reed (Phragmites australis) enclosed in leaf-bags of different mesh sizes. We demonstrated that leaf detritus of native black poplar decomposed twofold faster than the invasive common reed. We also found that the percentage of dry mass loss was significantly higher in medium/coarse litter bags compared to fine ones. However, microorganisms alone in fine mesh bags were able to decompose about 80% (poplar) and 60% (common reed) of the initial dry mass. No substantial differences were detected in structure, composition and functional organization of assemblages colonizing poplar and common reed leaf-bags. Therefore, differences in microbial activity and microbial/detritivore interactions rather than composition, diversity and abundance of the detritivore guild could better explain the faster breakdown of native leaves. Our results suggest that the substitution of natural riparian vegetation with invasive low-quality leaf plant species will have severe impacts on spring ecosystems. Alterations of structural and functional attributes of springs will be strictly related to the specific characteristics of plant invaders and to local conditions which may influence the detritivore/microbial contribution to leaf litter decomposition/breakdown.

Sedimentological implications of microbial mats, gypsum, and halite in Dhahban solar saltwork, Red Sea coast, Saudi Arabia

Microbial mats and gypsum exist in concentration ponds due to the first stage of evaporation, whereas halite is present in the crystallizers with continuous seawater evaporation, in the saltwork of Dhahban area, north of Jeddah city, Saudi Arabia. Several gypsum and halite facies types are distinguished in response to differences in microbial activity, salinity, topography of the ponds, water depth and wave energy. Two gypsum facies are recognized; planar–wavy gypsum microbialite and domal gypsum stromatolite at the relatively low salinity, inlet margin, and the relatively high salinity, outlet margin of the concentration ponds, respectively. They consist of fine and coarse, fibrous and swallowtail twin gypsum crystals that nucleate on the surface of microbial mats. Halite crystallizes at the brine surface as floating cumulates and rafts, and at the bottom of the ponds as vertically elongated chevrons and cornets. Lateral chevrons grow at the bottom of the ponds and at the brine surface in association with vertical chevrons and halite spheroids, respectively. Fluid-inclusion bands are regular and symmetrical in halite crystals, or show asymmetrical and indistinct layers in chevrons, and as a continuous layer over top of cumulates and rafts. This study suggests that saltworks represent a valuable ‘laboratory’ for the study of the primary depositional features of gypsum and halite crystals that are related to microbial activity, salinity, depth and/or energy conditions. The results can be used to infer physical energy conditions for deposition of gypsum and halite in ancient evaporitic basins.

Kinetics of arginine ammonification to estimate microbial activity of N mineralization in forest and cropland soils

The arginine mineralization assay has been used to estimate microbial potentials of soil ammonification, but the validity of saturating arginine dose must be assessed before applying the assay to forest soils as well as cropland soils. We studied the Michaelis–Menten kinetics of 14C-radiolabeled arginine mineralization (14CO2 production) at wide range of arginine doses (20–420 mg N kg−1 soil). The affinity constants (KM) of concentration-dependent mineralization rates (16–89 mg N kg−1 soil) increased with increasing soil N concentration but were even lower than the standard addition (140 mg N kg−1 soil). Arginine was selectively mineralized within 24 h in cropland soils, while arginine ammonification was slower in the coniferous forest soils with high C to N ratios (C/N > 20). The wide variation (11–90%) in the mineralization of arginine-derived N in 24 h is caused by the differences in microbial activities of arginine degradation and NH4+ release. This supports the validity of the arginine ammonification assay (140 mg N kg−1 soil addition and 24 h incubation) to obtain rough estimates of microbial potentials of ammonification in forest and cropland soils within the soil N concentrations studied (<10 g N kg−1). The ammonification assay showed the repressed activity of microbial N release in coniferous forest soils with high C/N ratios.

Microbial decomposition of porcine tissue in organic compost at different temperatures

Laboratory experiments were conducted to determine the effect of temperature (20 °C and 30 °C) on the rate of tissue decomposition in organic compost for a period of 28 days. Porcine tissue was used as a substitute for human body parts in burial microenvironment. Measurements of the decay include porcine tissue mass loss, soil pH, the metabolic activity of soil microbes, viable count and Gram stain of associated microflora. Incubation temperature had a significant impact on the post-mortem decay rates and stages at 30 °C in comparison to the samples incubated at 20 °C. Bacterial enumeration demonstrated microbial burden to be higher at higher temperatures, suggesting accelerated decomposition. Gram staining identified mostly Gram-negative bacteria, decomposers that might have originated from the organic meat as opposed to soil bacteria. There was a significant difference in soil pH levels during harvest times and at the end of the experiments in both microenvironments. It is an indication that measured pH of the depository may reveal whether the body parts were recently buried. A fluorescein diacetate (FDA) method that measured metabolic activity in compost demonstrated the highest release of fluorescein during harvests at 30 °C. A non-parametric Friedman test of differences among repeated measures rendered significant results (α=0.00) showing differences in microbial activity according to the temperature level. The results suggest that depositional microenvironment would be significantly modified by the decaying organic matter with the rise of temperature. This way, the temperature would make an impact on the decay of buried remains.

Linking abundance and community of microbial N2O-producers and N2O-reducers with enzymatic N2O production potential in a riparian zone

As aquatic-terrestrial ecotones, riparian zones are hotspots not only for denitrification but also for nitrous oxide (N2O) emission. Due to the potential role of nosZ II in N2O mitigation, emerging studies in terrestrial ecosystems have taken this newly reported N2O-reducer into account. However, our knowledge about the interactions between denitrification activities and both N2O-producers and reducers (especially for nosZ II) in aquatic ecosystems remains limited. In this study, we investigated spatiotemporal distributions of in situ N2O flux, potential N2O production rate, and potential denitrification rate, as well as of the related genes in a riparian zone of Baiyangdian Lake. Real-time quantitative PCR (qPCR) and high-throughput sequencing targeted functional genes were used to analyze the denitrifier communities. Results showed that great differences in microbial activities and abundances were observed between sites and seasons. Waterward sediments (constantly flooded area) had the lowest N2O production potential in both seasons. Not only the environmental factors (moisture content, NH4+ content and TOM) but also the community structure of N2O-producers and N2O-reducers (nirK/nirS and nosZ II/nosZ I ratios) could affect the potential N2O production rate. The abundance of the four functional genes in the winter was higher than in the summer, and the values all peaked at the occasionally flooded area in the winter. The dissimilarity in community composition was mainly driven by moisture content. Altogether, we propose that the N2O production potential was largely regulated by the community structure of N2O-producers and N2O-reducers in riparian zones. Increasing the constantly flooded area and reducing the occasionally flooded area of lake ecosystems may help reduce the level of denitrifier-produced N2O.

Ecosystem functioning in cities: Combined effects of urbanisation and forest size on early-stage leaf litter decomposition of European beech (Fagus sylvatica L.)

Environmental changes associated with urbanisation can affect the functioning of ecosystem processes. In cities, forests are among the most frequent types of green areas and provide a wide range of ecosystem services including air cleaning, decomposition of leaf litter and recreation. The European beech (Fagus sylvatica) is a frequent and widespread deciduous tree in temperate forests in Central Europe. In this study, we examined the effects of urbanisation on decomposition processes of F. sylvatica leaves in different-sized forests in the urban region of Basel, Switzerland. We used standardised litterbags (mesh size: 2mm) with F. sylvatica leaves to assess the impact of degree of urbanisation (indicated by the percentage cover of sealed area in the surroundings) and forest size on the early stage of leaf litter decomposition and seasonal microbial activity. We found combined effects of degree of urbanisation and forest size on the decomposition rate of leaf litter (klitter). Large forests showed the highest klitter in areas with sparse settlements and the lowest klitter in densely settled areas, whereas the opposite pattern was recorded for small and medium-sized forests. This indicates that abiotic and biotic forest characteristics of forests of similar size differently influenced klitter depending on the degree of urbanisation. Moisture content of litter was the best predictor of microbial activity, followed by forest size. We assume that factors acting at the landscape scale such as the degree of urbanisation might be too coarse to detect any differences in microbial activity. Our results revealed that even small urban forests contribute to this important ecosystem function. As decomposers are at the bottom of the food chain, management actions that support the biological activity in soil might be also beneficial for species at higher trophic ranks.

Peaks of in situ N2 O emissions are influenced by N2 O-producing and reducing microbial communities across arable soils.

Agriculture is the main source of terrestrial N2 O emissions, a potent greenhouse gas and the main cause of ozone depletion. The reduction of N2 O into N2 by microorganisms carrying the nitrous oxide reductase gene (nosZ) is the only known biological process eliminating this greenhouse gas. Recent studies showed that a previously unknown clade of N2 O-reducers (nosZII) was related to the potential capacity of the soil to act as a N2 O sink. However, little is known about how this group responds to different agricultural practices. Here, we investigated how N2 O-producers and N2 O-reducers were affected by agricultural practices across a range of cropping systems in order to evaluate the consequences for N2 O emissions. The abundance of both ammonia-oxidizers and denitrifiers was quantified by real-time qPCR, and the diversity of nosZ clades was determined by 454 pyrosequencing. Denitrification and nitrification potential activities as well as insitu N2 O emissions were also assessed. Overall, greatest differences in microbial activity, diversity, and abundance were observed between sites rather than between agricultural practices at each site. To better understand the contribution of abiotic and biotic factors to the insitu N2 O emissions, we subdivided more than 59,000 field measurements into fractions from low to high rates. We found that the low N2 O emission rates were mainly explained by variation in soil properties (up to 59%), while the high rates were explained by variation in abundance and diversity of microbial communities (up to 68%). Notably, the diversity of the nosZII clade but not of the nosZI clade was important to explain the variation of insitu N2 O emissions. Altogether, these results lay the foundation for a better understanding of the response of N2 O-reducing bacteria to agricultural practices and how it may ultimately affect N2 O emissions.

Kinetics and microbial community analysis for hydrogen production using raw grass inoculated with different pretreated mixed culture

In this study, five pretreatment methods (heat shock, acid, base, aeration and gamma radiation) were applied for enriching hydrogen producers from anaerobically digested sludge, aiming to compare their hydrogen fermentation performance using raw ryegrass as substrate. Results showed that various pretreatment methods caused great variations on grass hydrogen fermentation performance. Acid pretreatment was most efficient compared with other tested pretreatment methods, with relevant hydrogen yield of 64.4mL/g dry grass and organics removal of 31.4%. Kinetics results showed that the first-order kinetic model fitted hydrogen evolution better than the modified Gompertz model. Microbiological analysis showed that various pretreatment methods caused great variations on microbial activity and microbial community composition. Clostridium and Enterococcus were two dominant genera, while relative abundances of these two genera varied greatly for different pretreated samples. Difference in microbial activity and microbial community distribution induced by the pretreatment methods might directly cause different ryegrass fermentation performance.

Effects of wetting frequency and afforestation on carbon, nitrogen and the microbial community in soil

Afforestation of agricultural land is increasing, partly because it is an important biological method for reducing the concentration of atmospheric CO2 and potentially mitigating climate change. Rainfall patterns are changing and prolonged dry periods are predicted for many regions of the world, including southern Australia. To accurately predict land-use change potential for mitigating climate change, we need to have a better understanding of how changes in land-use (i.e. afforestation of pastures) may change the soils response to prolonged dry periods. We present results of an incubation study characterising C and N dynamics and the microbial community composition in soil collected from two tree plantings and their adjacent pastures under a baseline and reduced frequency. While the concentration of soil C was similar in pasture and tree planting soils, heterotrophic respiration was significantly lower in soil from pastures than tree plantings. Although there was little difference in the composition of the soil microbial community among any of the soils or treatments, differences in N cycling could indicate a difference in microbial activity, which may explain the differences in heterotrophic respiration between pastures and tree plantings. Soils from pastures and tree plantings responded similarly to a reduction in wetting frequency, with a decrease in microbial biomass (measured as total PLFA), and a similar reduction in heterotrophic respiration from the soil. This suggests that the responses to changes in future wetting cycles may be less dependent on land-use type than expected.

The use of PLFA analysis to detect differences in microbial activity in compost from horses treated with and without antibiotics

The use of PLFA analysis to detect differences in microbial activity in compost from horses treated with and without antibiotics

Soil Respiration and Bacterial Structure and Function after 17 Years of a Reciprocal Soil Transplant Experiment

The effects of climate change on soil organic matter—its structure, microbial community, carbon storage, and respiration response—remain uncertain and widely debated. In addition, the effects of climate changes on ecosystem structure and function are often modulated or delayed, meaning that short-term experiments are not sufficient to characterize ecosystem responses. This study capitalized on a long-term reciprocal soil transplant experiment to examine the response of dryland soils to climate change. The two transplant sites were separated by 500 m of elevation on the same mountain slope in eastern Washington state, USA, and had similar plant species and soil types. We resampled the original 1994 soil transplants and controls, measuring CO2 production, temperature response, enzyme activity, and bacterial community structure after 17 years. Over a laboratory incubation of 100 days, reciprocally transplanted soils respired roughly equal cumulative amounts of carbon as non-transplanted controls from the same site. Soils transplanted from the hot, dry, lower site to the cooler and wetter (difference of -5°C monthly maximum air temperature, +50 mm yr-1 precipitation) upper site exhibited almost no respiratory response to temperature (Q10 of 1.1), but soils originally from the upper, cooler site had generally higher respiration rates. The bacterial community structure of transplants did not differ significantly from that of untransplanted controls, however. Slight differences in local climate between the upper and lower Rattlesnake locations, simulated with environmental control chambers during the incubation, thus prompted significant differences in microbial activity, with no observed change to bacterial structure. These results support the idea that environmental shifts can influence soil C through metabolic changes, and suggest that microbial populations responsible for soil heterotrophic respiration may be constrained in surprising ways, even as shorter- and longer-term soil microbial dynamics may be significantly different under changing climate.