Hidden miners - The role of microorganisms under cover crops for phosphorus management

Phosphorus (P) is a limiting and non-renewable nutrient for which improper management is becoming a threat to food security and an environmental hazard for aquatic ecosystems. Phosphorus is particularly difficult to manage as complex physicochemical processes in the soil leave most P unavailable for crop uptake. Cover crops are a promising tool of agronomic management, which may increase P availability for the following crops through various mechanisms, such as an overall extended root system, greater P mobilization via exudation of organic anions, enhanced P mineralization by phosphatase excretion and microbial interactions. Better understanding of plant-microbial interactions offer the possibility to unravel the potential of cover crops for P management. In the frame of the EU Horizon2020 Project SoilCare we present the results of two studies in SW Germany about P dynamics under cover crops. The first field experiment investigated the effects of cover crop mixtures and no-tillage in a field experiment in the research station Tachenhausen of Nuertingen-Geislingen University, the second one studied the effects of single cover crop species in a low-P field near Rottenburg. The samples were analyzed for PLFA/NLFA content, enzymatic activities (acid and alkaline phospho-monoesterases and phosphodiesterase) and microbial P. The results reveal significant effects of cover crop mixtures on soil microbes, increasing their abundance and activity, as well as shifts in the microbial community structure. The effects were more pronounced near the soil surface and were still detectable more than one year after cover cropping in winter wheat. The microbial abundance, including Pmic and the activity of several enzymes of the P cycle were strongly increased in the rhizosphere of the cover crops. The results indicate that, under optimized agronomic management, the use of cover crops and minimum tillage can have measurable positive effects on the cycling of P in temperate agroecosystems

Microbial growth response to substrate complexity under different temperature regimes

Soil microbial communities mediate soil feedbacks to climate change and a thorough understanding of their response to increasing temperatures is central for predicting climate-induced changes in carbon fluxes. However, it is still unclear how microbial communities will change their structure and functions in response to temperature change and availability of organic carbon of varying complexity. Here, we present results from a lab-based study where soil microbial communities were exposed to different temperatures and organic C of different stability. Soil samples were collected from vegetated and bare fallow plots located in two regions in southwest Germany varying in climatic and edaphic conditions. Soils amended with cellobiose (CB), xylan or coniferyl alcohol (CA, lignin precursor) were incubated at 5, 15 and 25 °C. We generally found highest cumulative respiration (CO2-C) at 25 °C in all substrate treatments even though total microbial growth (measured as total extracted DNA) was higher at 15 °C. Fungal biomass (measured from ergosterol content and fungal PLFAs) responded significantly to added substrate and incubation temperature, with higher fungal biomass at 5 or 15 °C than 25 °C in all substrate amendments. Xylan addition resulted in significantly higher ergosterol contents than for CB and CA. Within region, land-use significantly affected fungal biomass response to added substrate; however, the temperature response was similar between fallow and vegetated plots. Bacterial community response was also significantly affected by substrate quality. In contrast to fungi, the growth response of Gram+ and Gram- bacteria declined in the order CB > xylan > CA. Currently, we are analyzing the qPCR data understand the response of different bacterial taxa to temperature and substrate complexity. Our results demonstrate the importance of the interaction between soil temperature and substrate quality for soil microbial community functions and growth strategies

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

Can soil improving cropping systems reduce the loss of soil biodiversity within agricultural soils?

Horizon 2020(H2020)Environmental Biolog

Phosphorus-acquisition strategies of canola, wheat and barley in soil amended with sewage sludges

Crops have different strategies to acquire poorly-available soil phosphorus (P) which are dependent on their architectural, morphological, and physiological root traits, but their capacity to enhance P acquisition varies with the type of fertilizer applied. The objective of this study was to examine how P-acquisition strategies of three main crops are affected by the application of sewage sludges, compared with a mineral P fertilizer. We carried out a 3-months greenhouse pot experiment and compared the response of P-acquisition traits among wheat, barley and canola in a soil amended with three sludges or a mineral P fertilizer. Results showed that the P-acquisition strategy differed among crops. Compared with canola, wheat and barley had a higher specific root length and a greater root carboxylate release and they acquired as much P from sludge as from mineral P. By contrast, canola shoot P content was greater with sludge than with mineral P. This was attributed to a higher rootreleased acid phosphatase activity which promoted the mineralization of sludge-derived P-organic. This study showed that contrasted P-acquisition strategies of crops allows increased use of renewable P resources by optimizing combinations of crop and the type of P fertilizer applied within the cropping system

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

Effect of nitrification inhibitors on the growth and activity of Nitrosotalea devanaterra in culture and soil

Peer reviewedPublisher PD

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

Impacts of organic and conventional crop management on diversity and activity of free-living nitrogen fixing bacteria and total bacteria are subsidiary to temporal effects

A three year field study (2007-2009) of the diversity and numbers of the total and metabolically active free-living diazotophic bacteria and total bacterial communities in organic and conventionally managed agricultural soil was conducted at the Nafferton Factorial Systems Comparison (NFSC) study, in northeast England. The result demonstrated that there was no consistent effect of either organic or conventional soil management across the three years on the diversity or quantity of either diazotrophic or total bacterial communities. However, ordination analyses carried out on data from each individual year showed that factors associated with the different fertility management measures including availability of nitrogen species, organic carbon and pH, did exert significant effects on the structure of both diazotrophic and total bacterial communities. It appeared that the dominant drivers of qualitative and quantitative changes in both communities were annual and seasonal effects. Moreover, regression analyses showed activity of both communities was significantly affected by soil temperature and climatic conditions. The diazotrophic community showed no significant change in diversity across the three years, however, the total bacterial community significantly increased in diversity year on year. Diversity was always greatest during March for both diazotrophic and total bacterial communities. Quantitative analyses using qPCR of each community indicated that metabolically active diazotrophs were highest in year 1 but the population significantly declined in year 2 before recovering somewhat in the final year. The total bacterial population in contrast increased significantly each year. Seasonal effects were less consistent in this quantitative study