Soil Microbial Biomass And Activity In A Cork Oak Savanna

Cork oak savannas are composed by a sparse tree canopy (30-70 trees/ha) and a grassland understory predominantly composed of C3 annuals that survive the hot and dry Mediterranean summers as seeds in the soil. Microbial communities can be more or less efficient at converting organic substrates into microbial biomass carbon depending on the quantity and quality of organic matter inputs. The cork oak savannas have two distinct types of plant litter that can affect soil microbial biomass and activity differently: herbaceous litter and the more recalcitrant woody plant litter resulting from the trees. Spatial variability of soil microbial biomass and activity due to the tree-grassland component of cork oak savannas were evaluated in order to better understand the soil carbon dynamics of these systems.

To quantify changes in soil microbial biomass and activity, measurements were performed in a Cork oak savanna in Southern Portugal. At this site 8 plots were randomly established under mature cork oak trees and paired with 8 open grassland plots. During one year soil cores (0-10 cm) were monthly collected at each site for measuring soil microbial biomass C and other eco-physiology parameters.


Results/Conclusion

Soil microbial biomass carbon (Cmic) and nitrogen (Nmic) were always higher under the tree canopy than in the open grasslands. Organic carbon (Corg) was also higher under the tree canopies. The Cmic/Corg ratio relates to the microbial activity and its potential to mineralize organic substances. The Cmic/Corg ratio was lower under the tree canopies than in the open grasslands. Less microbial biomass was supported per unit of Corg. Basal activity was always higher under the canopy than in the open grassland.

Trees scattered in the savanna function as islands inducing larger soil microbial communities and higher basal activity under the canopies. Lower Cmic/Corg ratio under the tree canopies suggests a more recalcitrant nature of the litter and a decrease in relative availability of organic matter under the trees.
&#xa

Metalliferous Biosignatures for Deep Subsurface Microbial Activity

Acknowledgments We thank the British Geological Survey (BGS) for the provision of samples and the Science & Technology Facilities Council (STFC) grant (ST/L001233/1) for PhD funding which aided this project. Research on selenium in reduction spheroids was also supported by NERC grants (NE/L001764/1 and NE/ M010953/1). The University of Aberdeen Raman facility was funded by the BBSRC. We also thank John Still for invaluable technical assistance.Peer reviewedPublisher PD

Hydrothermal activity lowers trophic diversity in Antarctic sedimented hydrothermal vents

Sedimented hydrothermal vents are those in which hydrothermal fluid vents through sediment and are among the least studied deep-sea ecosystems. We present a combination of microbial and biochemical data to assess trophodynamics between and within hydrothermally active and off-vent areas of the Bransfield Strait (1050–1647 m depth). Microbial composition, biomass and fatty acid signatures varied widely between and within vent and non-vent sites and provided evidence of diverse metabolic activity. Several species showed diverse feeding strategies and occupied different trophic positions in vent and non-vent areas and stable isotope values of consumers were generally not consistent with feeding structure morphology. Niche area and the diversity of microbial fatty acids reflected trends in species diversity and was lowest at the most hydrothermally active site. Faunal utilisation of chemosynthetic activity was relatively limited but was detected at both vent and non-vent sites as evidenced by carbon and sulphur isotopic signatures, suggesting that the hydrothermal activity can affect trophodynamics over a much wider area than previously thought

Soil biochemistry and microbial activity in vineyards under conventional and organic management at Northeast Brazil.

The São Francisco Submedium Valley is located at the Brazilian semiarid region and is an important center for irrigated fruit growing. This region is responsible for 97% of the national exportation of table grapes, including seedless grapes. Based on the fact that orgThe São Francisco Submedium Valley is located at the Brazilian semiarid region and is an important center for irrigated fruit growing. This region is responsible for 97% of the national exportation of table grapes, including seedless grapes. Based on the fact that organic fertilization can improve soil quality, we compared the effects of conventional and organic soil management on microbial activity and mycorrhization of seedless grape crops. We measured glomerospores number, most probable number (MPN) of propagules, richness of arbuscular mycorrhizal fungi (AMF) species, AMF root colonization, EE-BRSP production, carbon microbial biomass (C-MB), microbial respiration, fluorescein diacetate hydrolytic activity (FDA) and metabolic coefficient (qCO2). The organic management led to an increase in all variables with the exception of EE-BRSP and qCO2. Mycorrhizal colonization increased from 4.7% in conventional crops to 15.9% in organic crops. Spore number ranged from 4.1 to 12.4 per 50 g-1 soil in both management systems. The most probable number of AMF propagules increased from 79 cm-3 soil in the conventional system to 110 cm-3 soil in the organic system. Microbial carbon, CO2 emission, and FDA activity were increased by 100 to 200% in the organic crop. Thirteen species of AMF were identified, the majority in the organic cultivation system. Acaulospora excavata, Entrophospora infrequens, Glomus sp.3 and Scutellospora sp. were found only in the organically managed crop. S. gregaria was found only in the conventional crop. Organically managed vineyards increased mycorrhization and general soil microbial activity

Augmenting Biogas Process Modeling by Resolving Intracellular Metabolic Activity

The process of anaerobic digestion in which waste biomass is transformed to methane by complex microbial communities has been modeled for more than 16 years by parametric gray box approaches that simplify process biology and do not resolve intracellular microbial activity. Information on such activity, however, has become available in unprecedented detail by recent experimental advances in metatranscriptomics and metaproteomics. The inclusion of such data could lead to more powerful process models of anaerobic digestion that more faithfully represent the activity of microbial communities. We augmented the Anaerobic Digestion Model No. 1 (ADM1) as the standard kinetic model of anaerobic digestion by coupling it to Flux-Balance-Analysis (FBA) models of methanogenic species. Steady-state results of coupled models are comparable to standard ADM1 simulations if the energy demand for non-growth associated maintenance (NGAM) is chosen adequately. When changing a constant feed of maize silage from continuous to pulsed feeding, the final average methane production remains very similar for both standard and coupled models, while both the initial response of the methanogenic population at the onset of pulsed feeding as well as its dynamics between pulses deviates considerably. In contrast to ADM1, the coupled models deliver predictions of up to 1,000s of intracellular metabolic fluxes per species, describing intracellular metabolic pathway activity in much higher detail. Furthermore, yield coefficients which need to be specified in ADM1 are no longer required as they are implicitly encoded in the topology of the species’ metabolic network. We show the feasibility of augmenting ADM1, an ordinary differential equation-based model for simulating biogas production, by FBA models implementing individual steps of anaerobic digestion. While cellular maintenance is introduced as a new parameter, the total number of parameters is reduced as yield coefficients no longer need to be specified. The coupled models provide detailed predictions on intracellular activity of microbial species which are compatible with experimental data on enzyme synthesis activity or abundance as obtained by metatranscriptomics or metaproteomics. By providing predictions of intracellular fluxes of individual community members, the presented approach advances the simulation of microbial community driven processes and provides a direct link to validation by state-of-the-art experimental techniques

Changes in the Soil Microbial Hydrolytic Activity and the Content of Organic Carbon and Total Nitrogen by Growing Spring Barley Undersown with Red Clover in Different Farming Systems

The experiments were carried out during 2012–2017. There were 5 crops in rotation: Red clover, winter wheat, pea, potato and barley undersown (us) with red clover. There were 5 cropping systems in the experimental setup: 2 conventional systems with chemical plant protection and mineral fertilizers; 3 organic systems which included winter cover crops and farm manure. The aim of the present research was to study the e_ect of cultivating barley undersown with red clover and the preceding winter cover crop on the soil microbial hydrolytic activity, the change in the content of soil organic carbon (SOC) and total nitrogen (Ntot) compared to the same parameters from the field that was previously under potato cultivation (forecrop of barley in the rotation). The cultivation of barley with red clover (barley (us)) had a positive impact on the soil micro-organisms activity. In organic systems the soil microbial hydrolytic activity increased on average by 19.0%, compared to the conventional systems. By cultivating barley (us) the soil microbial hydrolytic activity had a significant e_ect on the SOC content only in organic systems where winter cover crops were used. Organic cultivation systems had positive impact on the soil nitrogen content; Ntot in samples taken before sowing the barley (us) was higher by 17.4% and after the cultivation of barley (us) by 14.4% compared to conventional systems, as an average of experimental years. After cultivation of barley (us) with red clover the soil microbial hydrolytic activity had no e_ect on the soil Ntot content in either cultivation systems

Nutrient availability affects carbon turnover and microbial physiology differently in topsoil and subsoil under a temperate grassland

Increasing subsoil organic carbon inputs could potentially mitigate climate change by sequestering atmospheric CO2. Yet, microbial turnover and stabilization of labile carbon in subsoils are regulated by complex mechanisms including the availability of nitrogen (N), phosphorous (P), and sulfur (S). The present study mimicked labile organic carbon input using a versatile substrate (i.e. glucose) to address the interaction between carbon-induced mineralization, N-P-S availability, and microbial physiology in topsoil and subsoils from a temperate agricultural sandy loam soil. A factorial incubation study (42 days) showed that net losses of added carbon in topsoil were constant, whereas carbon losses in subsoils varied according to nutrient treatments. Glucose added to subsoil in combination with N was fully depleted, whereas glucose added alone or in combination with P and S was only partly depleted, and remarkably 59–92% of the added glucose was recovered after the incubation. This showed that N limitation largely controlled carbon turnover in the subsoil, which was also reflected by microbial processes where addition of glucose and N increased β-glucosidase activity, which was positively correlated to the maximum CO2 production rate during incubation. The importance of N limitation was substantiated by subsoil profiles of carbon source utilization, where microbial metabolic diversity was mainly related to the absence or presence of added N. Overall, the results documented that labile carbon turnover and microbial functions in a temperate agricultural subsoil was controlled to a large extent by N availability. Effects of glucoseinduced microbial activity on subsoil physical properties remained ambiguous due to apparent chemical effects of N (nitrate) on clay dispersibility

Impact of soil management on the functional activity of microbial communities associated to cork oak rhizosphere

The microbial ecology of cork oak rhizosphere was investigated using the Biolog community level physiological profile (CLPP) that provides a unique metabolic fingerprint helpful for the characterization of complex microbial communities. Microbial populations from the rhizosphere of cork oak plants growing at three different sites within the same area were characterized using CLPP and compared. The sites were distinguished by a different soil management under the tree cover and, in general terms, by a different anthropogenic impact. The comparison of metabolic fingerprints of the different microbial populations showed the existence of a relationship between general microbial activity and functional biodiversity in the rhizosphere and the level of anthropogenic impact. Particularly the presence of grazing animals, soil tillage and fire could be identified as the main factors affecting both the general microbial activity and the structure of microbial populations from cork oak rhizospheres

Microbial metal resistance and metabolism across dynamic landscapes: high-throughput environmental microbiology.

Multidimensional gradients of inorganic compounds influence microbial activity in diverse pristine and anthropogenically perturbed environments. Here, we suggest that high-throughput cultivation and genetics can be systematically applied to generate quantitative models linking gene function, microbial community activity, and geochemical parameters. Metal resistance determinants represent a uniquely universal set of parameters around which to study and evaluate microbial fitness because they represent a record of the environment in which all microbial life evolved. By cultivating microbial isolates and enrichments in laboratory gradients of inorganic ions, we can generate quantitative predictions of limits on microbial range in the environment, obtain more accurate gene annotations, and identify useful strategies for predicting and engineering the trajectory of natural ecosystems