Auto- und Heterotrophic Respiration in the Hohenheim Climate Change Experiment - The Importance of Temperature Change and Vegetation Period

Current Climate change (CC) research in soil science mainly focusses on natural ecosystems, without considering the potential of agro-ecosystems for feedback mechanisms to CC and CC mitigation through Carbon(C)-sequestration. We expect that CC induces increasing water limitation under elevated temperature, lowers the intensity of soil respiration and changes the ratio between the amount of root-dependent and basal soil respiration. Such changes might be due to differences in the intrinsic temperature and moisture sensitivity of microbial and root respiration and due to altered root exudation. In this project, we focus on CC-induced effects on plant-dependent and basal soil respiration to improve the estimation of long-term soil organic matter stabilization. Within the Hohenheim Climate Change (HoCC) experiment (established in 2008), barley plants were pulse-labelled with 20-atom% 13CO2 for 4 h using ventilated transparent chambers on warmed and control plots in an agricultural field. The labeling was done during three different stages (advanced tillering, booting and grain-filling) of the vegetation period, at which C-sink strength of shoot and root differs according to plant development. CO2-fluxes and isotopic composition were measured in real time in the field for the first 50h (post labeling) using a 13CO2 isotope analyzer. Results from tracing 13C-fluxes will clarify how soil moisture and long-term elevated temperature affect the overall C-balance in agricultural soils in dependence of the vegetation period. This will allow estimations of direction and strength of feedback mechanisms of terrestrial C-cycling under CC. Overall, insights obtained in this project will provide better understanding of the CC impact on and of temperate agricultural production systems

Microbial carbon turnover in the detritusphere

Microbial decomposition processes at the soil-litter interface involves a complex food web including fungi, bacteria, and archaea that compete for the organic matter. During the decomposition, the nutrient quantity and quality changes as well as the microbial community composition. It is still a challenge to identify and quantify active microbial species in concurrency with their absolute contribution to the carbon (C) turnover. In the frame of the DFG-Project (FOR 918) “Carbon flow in belowground food webs assessed by isotope tracers“ we determined the C flow and turnover of differently aged maize litter in bacteria and fungi of an arable soil. A microcosm experiment was set up with C-13-labeled and unlabeled maize litter on top of soil cores. A reciprocal transplantation of the labeled litter on soil cores with unlabeled litter allowed us to follow the C flow into different microbial groups at the early (0-4d), intermediate (4-12d) and late stage (28-36d) of litter decomposition. We analyzed microbial CO2 respiration, microbial biomass and PLFA pattern in the top 3 mm of the soil cores. To identify and quantify microbial species feeding on the substrate and to assess their degree of C-13 assimilation, DNA stable isotope probing followed by gene-targeted sequencing of bacteria and fungi are currently performed on the soil metagenome. We expected specific microbial communities (copio- and oligotrophic) involved in maize litter decomposition at the different stages of litter decay. During the initial days of the experiment, up to 17% of the CO2-C was maize-derived C. The C-13 content in the CO2 decreased with continuous decomposition of the litter. The highest absolute amount of maize-derived C was found in gram-positive bacteria in the early stage of litter decomposition. For fungi, the highest maize C incorporation was in the intermediate stage of litter decomposition. We calculated a faster C turnover in the fungal biomass than in the bacterial biomass for all three decomposition stages. But during the later stage of litter decomposition, maize-derived C was less utilized by both bacteria and fungi. These results will be concluded by the quantitative DNA-SIP method to provide a species-resolved contribution to the C turnover in the microbial food web at different decomposition stages in the detritusphere

Divergent drivers of the microbial methane sink in temperate forest and grassland soils

Aerated topsoils are important sinks for atmospheric methane (CH4) via oxidation by CH4‐oxidizing bacteria (MOB). However, intensified management of grasslands and forests may reduce the CH4 sink capacity of soils. We investigated the influence of grassland land‐use intensity (150 sites) and forest management type (149 sites) on potential atmospheric CH4 oxidation rates (PMORs) and the abundance and diversity of MOB (with qPCR) in topsoils of three temperate regions in Germany. PMORs measurements in microcosms under defined conditions yielded approximately twice as much CH4 oxidation in forest than in grassland soils. High land‐use intensity of grasslands had a negative effect on PMORs (−40%) in almost all regions and fertilization was the predominant factor of grassland land‐use intensity leading to PMOR reduction by 20%. In contrast, forest management did not affect PMORs in forest soils. Upland soil cluster (USC)‐α was the dominant group of MOBs in the forests. In contrast, USC‐γ was absent in more than half of the forest soils but present in almost all grassland soils. USC‐α abundance had a direct positive effect on PMOR in forest, while in grasslands USC‐α and USC‐γ abundance affected PMOR positively with a more pronounced contribution of USC‐γ than USC‐α. Soil bulk density negatively influenced PMOR in both forests and grasslands. We further found that the response of the PMORs to pH, soil texture, soil water holding capacity and organic carbon and nitrogen content differ between temperate forest and grassland soils. pH had no direct effects on PMOR, but indirect ones via the MOB abundances, showing a negative effect on USC‐α, and a positive on USC‐γ abundance. We conclude that reduction in grassland land‐use intensity and afforestation has the potential to increase the CH4 sink function of soils and that different parameters determine the microbial methane sink in forest and grassland soils.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659ESFMinistry of Education, Science and Culture of Mecklenburg‐Western PomeraniaPeer Reviewe

Beeinflusst die Landnutzungsintensität im Grünland die mikrobielle Besiedlung von organo-mineralischen Komplexen sowie die Ressourcenverteilung innerhalb der mikrobiellen Bodengemeinschaft?

Minerale bzw. die Oberflächen von organo-mineralischen Komplexen sind neben der Rhizo- und Detritussphäre mikrobielle ´Hot Spots` in Böden. Die Besiedlung dieser Mikrohabitate ist abhängig von biotischen und abiotischen Eigenschaften des Bodens. Es ist daher anzunehmen, dass unterschiedliche mikrobielle Ressourcennutzungsstrategien zur räumlichen Verteilung von Bodenmikroorganismen auf lokaler Ebene beitragen können. Bis heute ist unklar, inwiefern sich dies auf die Struktur und Funktion der mikrobiellen Gemeinschaft unter Freilandbedingungen in Grünlandböden auswirkt. Im Rahmen der Biodiversitäts-Exploratorien versuchen wir zwei Forschungsfragen zu beantworten 1) Welche Organismen sind beim Wurzelabbau in Grünlandböden unter verschiedenen Landnutzungsintensitäten die Hauptakteure? 2) Wer profitiert wann am meisten? Hierzu wurde innerhalb des Forschungsprojektes im September 2014 ein randomisiertes Feldexperiment mit Mikrokosmen auf 10 Flächen der Schwäbischen Alb angelegt. Die Flächen unterscheiden sich in ihrer Landnutzungsintensität (fünf Flächen mit hohem und fünf mit niedrigem LUI-Index), nicht aber hinsichtlich des Bodentyps (Rendzina). Befüllt wurde jeder Mikrokosmos mit einem standortangepassten Mineral-Wurzelgemisch bestehend aus: 71,4% Illit, 9,6% Goethit, 17% Quarz-Schluff und 2% Quarzsand sowie doppelt markierten Feinwurzeln, Dactylis glomerata/ Lolium perenne (13,1 Atom-% C-13 und 12,1 Atom-% N-15). Die Ernte der Mikrokosmen, des angrenzenden Bodens sowie der Vegetation direkt über den Mikrokosmen wird nach 1, 3, 6, 12 und 18 Monaten durchgeführt. Zur Beantwortung der Forschungsfragen werden a) die mikrobielle Gemeinschaftsstruktur mit Hilfe von CFE, PLFA und molekularbiologischen Methoden (qPCR), sowie b) das mikrobielle Nahrungsnetz mittels isotopischer Verfahren analysiert

Unraveling spatiotemporal variability of arbuscular mycorrhizal fungi in a temperate grassland plot

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Goldmann, K., Boeddinghaus, R. S., Klemmer, S., Regan, K. M., Heintz-Buschart, A., Fischer, M., Prati, D., Piepho, H., Berner, D., Marhan, S., Kandeler, E., Buscot, F., & Wubet, T. Unraveling spatiotemporal variability of arbuscular mycorrhizal fungi in a temperate grassland plot. Environmental Microbiology, 22(3),(2020): 873-888, doi:10.1111/1462-2920.14653.Soils provide a heterogeneous environment varying in space and time; consequently, the biodiversity of soil microorganisms also differs spatially and temporally. For soil microbes tightly associated with plant roots, such as arbuscular mycorrhizal fungi (AMF), the diversity of plant partners and seasonal variability in trophic exchanges between the symbionts introduce additional heterogeneity. To clarify the impact of such heterogeneity, we investigated spatiotemporal variation in AMF diversity on a plot scale (10 × 10 m) in a grassland managed at low intensity in southwest Germany. AMF diversity was determined using 18S rDNA pyrosequencing analysis of 360 soil samples taken at six time points within a year. We observed high AMF alpha‐ and beta‐diversity across the plot and at all investigated time points. Relationships were detected between spatiotemporal variation in AMF OTU richness and plant species richness, root biomass, minimal changes in soil texture and pH. The plot was characterized by high AMF turnover rates with a positive spatiotemporal relationship for AMF beta‐diversity. However, environmental variables explained only ≈20% of the variation in AMF communities. This indicates that the observed spatiotemporal richness and community variability of AMF was largely independent of the abiotic environment, but related to plant properties and the cooccurring microbiome.We thank the managers of the three Exploratories, Kirsten Reichel‐Jung, Swen Renner, Katrin Hartwich, Sonja Gockel, Kerstin Wiesner, and Martin Gorke for their work in maintaining the plot and project infrastructure; Christiane Fischer and Simone Pfeiffer for giving support through the central office, Michael Owonibi and Andreas Ostrowski for managing the central data base, and Eduard Linsenmair, Dominik Hessenmöller, Jens Nieschulze, Ernst‐Detlef Schulze, Wolfgang W. Weisser and the late Elisabeth Kalko for their role in setting up the Biodiversity Exploratories project. The work has been funded by the DFG Priority Program 1374 ‘Infrastructure‐Biodiversity‐Exploratories’ (BU 941/22‐1, BU 941/22‐3, KA 1590/8‐2, KA 1590/8‐3). Field work permits were issued by the responsible state environmental office of Baden‐Württemberg (according to § 72 BbgNatSchG). Likewise, we kindly thank Beatrix Schnabel, Melanie Günther and Sigrid Härtling for 454 sequencing in Halle. AHB gratefully acknowledges the support of the German Centre for Integrative Biodiversity Research (iDiv) Halle‐Jena‐Leipzig funded by the German Research Foundation (FZT 118). Authors declare no conflict of interests

Reviewing the Carbonation Resistance of Concrete

The paper reviews the studies on one of the important durability properties of concrete i.e. Carbonation. One of the main causes of deterioration of concrete is carbonation, which occurs when carbon dioxide (CO2) penetrates the concrete’s porous system to create an environment with lower pH around the reinforcement in which corrosion can proceed. Carbonation is a major cause of degradation of concrete structures leading to expensive maintenance and conservation operations. Herein, the importance, process and effect of various parameters such as water/cement ratio, water/binder ratio, curing conditions, concrete cover, super plasticizers, type of aggregates, grade of concrete, porosity, contaminants, compaction, gas permeability, supplementary cementitious materials (SCMs)/ admixtures on the carbonation of concrete has been reviewed. Various methods for estimating the carbonation depth are also reported briefl

Effects of warming and drought on potential N2O emissions and denitrifying bacteria abundance in grasslands with different land-use

Increased warming in spring and prolonged summer drought may alter soil microbial denitrification. We measured potential denitrification activity and denitrifier marker gene abundances (nirK, nirS, nosZ) in grasslands soils in three geographic regions characterized by site-specific land-use indices (LUI) after warming in spring, at an intermediate sampling and after summer drought. Potential denitrification was significantly increased by warming, but did not persist over the intermediate sampling. At the intermediate sampling, the relevance of grassland land-use intensity was reflected by increased potential N2O production at sites with higher LUI. Abundances of total bacteria did not respond to experimental warming or drought treatments, displaying resilience to minor and short-term effects of climate change. In contrast, nirS- and nirK-type denitrifiers were more influenced by drought in combination with LUI and pH, while the nosZ abundance responded to the summer drought manipulation. Land-use was a strong driver for potential denitrification as grasslands with higher LUI also had greater potentials for N2O emissions. We conclude that both warming and drought affected the denitrifying communities and the potential denitrification in grassland soils. However, these effects are overruled by regional and site-specific differences in soil chemical and physical properties which are also related to grassland land-use intensit

Temporal and small-scale spatial variation in grassland productivity, biomass quality, and nutrient limitation

Characterization of spatial and temporal variation in grassland productivity and nutrition is crucial for a comprehensive understanding of ecosystem function. Although within-site heterogeneity in soil and plant properties has been shown to be relevant for plant community stability, spatiotemporal variability in these factors is still understudied in temperate grasslands. Our study aimed to detect if soil characteristics and plant diversity could explain observed small-scale spatial and temporal variability in grassland productivity, biomass nutrient concentrations, and nutrient limitation. Therefore, we sampled 360 plots of 20 cm × 20 cm each at six consecutive dates in an unfertilized grassland in Southern Germany. Nutrient limitation was estimated using nutrient ratios in plant biomass. Absolute values of, and spatial variability in, productivity, biomass nutrient concentrations, and nutrient limitation were strongly associated with sampling date. In April, spatial heterogeneity was high and most plots showed phosphorous deficiency, while later in the season nitrogen was the major limiting nutrient. Additionally, a small significant positive association between plant diversity and biomass phosphorus concentrations was observed, but should be tested in more detail. We discuss how low biological activity e.g., of soil microbial organisms might have influenced observed heterogeneity of plant nutrition in early spring in combination with reduced active acquisition of soil resources by plants. These early-season conditions are particularly relevant for future studies as they differ substantially from more thoroughly studied later season conditions. Our study underlines the importance of considering small spatial scales and temporal variability to better elucidate mechanisms of ecosystem functioning and plant community assembly

Stochastic Dispersal Rather Than Deterministic Selection Explains the Spatio-Temporal Distribution of Soil Bacteria in a Temperate Grassland

Spatial and temporal processes shaping microbial communities are inseparably linked but rarely studied together. By Illumina 16S rRNA sequencing, we monitored soil bacteria in 360 stations on a 100 square meter plot distributed across six intra-annual samplings in a rarely managed, temperate grassland. Using a multi-tiered approach, we tested the extent to which stochastic or deterministic processes influenced the composition of local communities. A combination of phylogenetic turnover analysis and null modeling demonstrated that either homogenization by unlimited stochastic dispersal or scenarios, in which neither stochastic processes nor deterministic forces dominated, explained local assembly processes. Thus, the majority of all sampled communities (82%) was rather homogeneous with no significant changes in abundance-weighted composition. However, we detected strong and uniform taxonomic shifts within just nine samples in early summer. Thus, community snapshots sampled from single points in time or space do not necessarily reflect a representative community state. The potential for change despite the overall homogeneity was further demonstrated when the focus shifted to the rare biosphere. Rare OTU turnover, rather than nestedness, characterized abundance-independent β-diversity. Accordingly, boosted generalized additive models encompassing spatial, temporal and environmental variables revealed strong and highly diverse effects of space on OTU abundance, even within the same genus. This pure spatial effect increased with decreasing OTU abundance and frequency, whereas soil moisture – the most important environmental variable – had an opposite effect by impacting abundant OTUs more than the rare ones. These results indicate that – despite considerable oscillation in space and time – the abundant and resident OTUs provide a community backbone that supports much higher β-diversity of a dynamic rare biosphere. Our findings reveal complex interactions among space, time, and environmental filters within bacterial communities in a long-established temperate grassland

Carbon budgets of top- and subsoil food webs in an arable system

© 2018 This study assessed the carbon (C) budget and the C stocks in major compartments of the soil food web (bacteria, fungi, protists, nematodes, meso- and macrofauna) in an arable field with/without litter addition. The C stocks in the food web were more than three times higher in topsoil (0–10 cm) compared to subsoil (>40 cm). Microorganisms contained over 95% of food web C, with similar contributions of bacteria and fungi in topsoil. Litter addition did not alter C pools of soil biota after one growing season, except for the increase of fungi and fungal feeding nematodes in the topsoil. However, the C budget for functional groups changed with depth, particularly in the microfauna. This suggests food web resilience to litter amendment in terms of C pool sizes after one growing season. In contrast, the distinct depth dependent pattern indicates specific metacommunities, likely shaped by dominant abiotic and biotic habitat properties