Publications

Climate and root proximity as dominant drivers of enzyme activity and C and N isotopic signature in soil

No abstract is provided for this article.

Assessing microbial utilization of free versus sorbed Alanine by using position-specific 13C labeling and 13C-PLFA analysis

No abstract is provided for this article.

Active metabolic pathways of anaerobic methane oxidation in paddy soils

Anaerobic oxidation of methane (AOM) is a globally important CH4 sink. However, the AOM pathways in paddy soils, the largest agricultural source of methane emissions (31 Mio tons per year) are not yet well described. Here, a combination of 13C isotope tracer, phospholipid fatty acids (PLFA) analyses, and microbial community analysis was used to identify AOM pathways in fertilized (pig manure, biochar, NPK, and the control) paddy soils amended with alternative electron acceptors (AEAs) (NO3 −, Fe3+, SO4 2−, humic acids, and the reference without AEAs addition). After 84 days of anaerobic incubation, the microbial co-occurrence network got tightened and became more complex relative to unincubated samples. Fertilization and AEAs addition led to a strong divergence of the microbial community structure as indicated by abundances of AOM-related microbiota and 13C incorporation into microbial PLFA, thus suggesting an environmental niche differentiation of AOM-involved microorganisms. Comparative analyses revealed a set of major and minor AOM pathways with synergistic relations to complementary anaerobic microbial groups. NO3 −-driven AOM, performed by members of the candidate group ANME-2d, was the major AOM pathway. Minor AOM pathways involved NO2 − reduction by NC10, reduction of humic acids and Fe3+ by Geobacter species, and SO4 2− reduction by sulfate-reducing bacteria linked with anaerobic methanotrophs. As identified by the network analysis, these active AOM pathways compensated a fraction of CH4 produced during ongoing methanogenesis. From a broader ecological perspective, nitrogen-driven AOM will become a more important methane sink in the future with the increases of nitrogen fertilization and deposition.

Identification of spatial biochemical pattern in the rhizosphere by linkage between rhizodeposition and enzyme activities

No abstract is provided for this article.

Microbial utilization of sugars in soil assessed by position-specific labeling and compound-specific 13C-PLFA-analysis

No abstract is provided for this article.

Recycling of extracellular metabolites exceeds biomass de-novo synthesis

No abstract is provided for this article.

Disaggregated data for: "Mucilage Polysaccharide Composition and Exudation in Maize From Contrasting Climatic Regions"

Managing climatic risk in cocoa by designing resilient agroforestry systems based on a functional trait approach

Climate change projections indicate that significant areas of the current cocoa cultivation areas in West Africa are likely to experience unfavorable climatic conditions by 2050. Water use efficient agroforestry systems are considered to be an important option to adapt cocoa to climate change. Water use efficiency and complementary soil water use between cocoa and shade trees have been reported in previous studies in Indonesia but in our previous study in Ghana, popular native shade tree species Albizia ferruginea and Antiaris toxicaria were found to have a strong competitive water use advantage over cocoa plants during an extreme drought experienced during 2015/16. Cocoa plants under no shade were relatively more resilient with higher survival rate and post drought recovery.While past research studies   were each limited to few selected shade tree species being investigated despite the huge numbers within cocoa landscapes. To overcome this limitation, an approach based on functional traits of trees in terms of water use is proposed to understand their effect on water use efficiency and drought resilience in cocoa agroforestry systems rather than describing individual species. We apply this concept across temporal and spatial scales in a marginally suitable cocoa climate in Ghana. Shade tree species have been categorized into phenological trait groups (evergreen, deciduous, or brevi-deciduous) under which detailed above- and belowground traits interactions with cocoa plant and effect on water use has been evaluated.The following hypotheses are being tested: (i) shade trees in the three phenological trait groups exhibit significant difference in their root and water uptake depth, and, thus, affect environmental conditions relevant for cocoa, (ii) cocoa plant above- and belowground morphological and physiological traits are influenced by shade tree phenological and morphological traits and their modification by micro-climatic (light, temperature, relative humidity and VPD), and soil (water and nutrients) conditions over different seasons.Replicated plots of 19 shade tree species distributed across the three phenological trait groups have been established for analysis of functional traits interactions in such a multi-species agroforestry system. We determine root specific traits through direct sampling, stable isotope analysis for assessment of water use portioning between the various shade tree groups and cocoa plants. Soil moisture, temperature and relative humidity and light sensors were installed in each plot. Cocoa plants under different micro-climatic impact zones of the shade trees have been monitored for a full production cycle.  The shade trees impact on the cocoa plant productivity (morphology and yield traits) has been evaluated. Complementary and non-complementary shade tree species with respect to their trait interactions and effect on cocoa plant productivity have been identified.

Combined biochar and nitrogen application stimulates enzyme activity and root plasticity

Biochar (BC) and nitrogen (N) fertilizers are frequently applied to improve soil properties and increase crop productivity. Nonetheless, our mechanistic understanding of plant-soil interactions under single or combined application of BC and N remains incomplete. For the first time, we applied a split-root system to evaluate how BC or N contributes to the changes in soil enzyme activities, N and phosphorus (P) cycling as well as root plasticity. Left and right parts of rhizoboxes were filled with silty-clay loamy soil amended with BC (15 g kg−1 soil, from wheat straw, 300 °C), N (0.05 g KNO3-N kg−1 soil) or a control (no amendments), resulting in the following combinations: BC/Control, N/Control, BC/N. Soil enzyme activities, available N and P, root morphology and plant biomass were analyzed after plant harvest. Plant biomass (shoot + root) ranged from 0.56 g pot−1 (BC/Control) to 0.91 g pot−1(BC/N). The decreased soil bulk density and increased P availability in the BC compartment (BC/Control and BC/N) stimulated root length by 1.4–1.8 times – an effect that was independent of N availability in the same rhizobox. Biochar stimulated activities of β-glucosidase and leucine aminopeptidase (by 33–39%) compared to N due to the coupling of C, N and P cycles in BC/N treated soil. Nitrogen fertilization also increased β-glucosidase activity compared to the unfertilized control, whereas root elongation remained unaffected. Thus, the combined application of BC/N had more efficient benefits for plant growth than BC or N alone. This is linked with i) the stimulation of enzyme activities at the BC locations to reduce N limitation for both microorganisms and plants, and ii) an increase of fine root production to improve N uptake efficiency. Thus, combined BC/N application is potentially especially sustainable to overcome nutrient limitation as well as to maintain crop productivity because it accelerates root-microbial interactions.

Resistance of microbial community and its functional sensitivity in the rhizosphere hotspots to drought

Climate change impacts soil microbial communities, activities and functionality. Nonetheless, responses of the microbiome in soil microenvironments with contrasting substrate availability in the rhizosphere to climatic stresses such as drought are largely unknown. To fill this knowledge gap, we coupled soil zymography with site-specific micro-sampling of the soil and subsequent high-throughput sequencing. This helped identify how the bacterial community structure and the genes encoding N-cycling enzymes (leucine aminopeptidase and chitinase) in rhizosphere hotspots and coldspots (microsites with activities in the range of bulk soil but localized within the rhizosphere) of maize respond to drought (20% WHC, two weeks). The elevated activities of leucine aminopeptidase and chitinase in rhizosphere hotspots were caused by the tight collaborative relationships between bacteria and their stable network structure rather than by any significant shift in bacterial community structure or enzyme-encoding gene copies. Despite the similarity in bacterial community structure in soil under drought and optimal moisture, functional predictions indicated the increased relative abundance of genera belonging to Actinobacteria capable of leucine aminopeptidase and chitinase production, especially Streptomyces, Nocardioides, Marmoricola, and Knoellia. Accordingly, the number of gene copies encoded by Actinobacteria for these two enzymes increased by 5.0–17% under drought. Among the bacteria with increased relative abundance under drought, Luedemannella played a crucial role in mediating nutrients and energy fluxes between bacteria. This was reflected in a 35–70% increase in leucine aminopeptidase and chitinase activities under drought. The resistance of enzyme activities to drought was higher in hotpots than that in coldspots. These results revealed that rhizosphere bacterial community composition remained stable, and that the number of gene copies encoded by Actinobacteria responsible for N-cycling enzymes increased under drought. The expected reduction of processes of N cycle was absent. Instead, bacteria increased N mining rate in those hotspots remaining active despite water scarcity.

Tracing C Fluxes through the Metabolic Network of Soil Microbial Communities by Position-Specific Labeling

No abstract is provided for this article.

From Position-Specific Labeling to Environmental Fluxomics: Elucidating Biogeochemical Cycles from the Metabolic Perspective (BG Division Outstanding ECS Award Lecture)

No abstract is provided for this article.

Assessing the sustainability of land use management of northern Ethiopian drylands by various indicators for soil health

Land use change and agricultural intensification in developing countries affect terrestrial carbon (C) stocks, CO2 efflux, microbial communities and overall soil health. This study assesses the effects of four land use types typical for northern Ethiopia (forests, exclosures, grazing lands and intensively cultivated croplands) on various soil health indicators. We quantified and compared microbial biomass carbon (MBC), water extractable organic carbon (WOC), metabolic quotient (qCO2), substrate use efficiency (SUE) and dynamics of 14C-labelled glucose added to soil. Irrespective of the land use, MBC but not SUE decreased 2- to 8-fold with increasing depth, demonstrating the C limitation of subsoil microbial communities under all land use forms. Sandy soils, however, which permit seepage and leaching of WOC into lower layers and promote subsoil microbial communities, adapted to frequent input of easily accessible C substrates. Significantly higher qCO2 were recorded in subsoils compared to topsoils, especially in croplands with low MBC. In croplands, high glucose-14C incorporation (≈20%) into their low microbial biomass indicates a high SUE and reflects a better nutrient supply of these microbial communities. Mineralization of up to 95% of 14C-labeled glucose in topsoils of forest and grazing lands was higher than in croplands, and exclosures never reached the level of natural ecosystems. This demonstrates that 6–10 years of exclosure establishment does not result in soil microbial communities and soil C dynamics resembling those of natural forests. Our study demonstrates that land use can negatively affect the ecological performance of microbial communities and that these impacts are more severe in sandy than in clayey soils. Mitigation strategies such as minimum tillage or residue retention in intensively cultivated croplands can increase microbial abundance and activity and help ensure environmental sustainability and mitigation of climate change. Nonetheless, such measures need to be carefully accompanied by monitoring indicators of soil health to confirm the sustainability of the chosen mitigation strategies.

Effect of environmental conditions on the fatty acid fingerprint of microbial communities

No abstract is provided for this article.

Extracellular enzyme activity and stoichiometry: The effect of soil microbial element limitation during leaf litter decomposition

To explore carbon (C), nitrogen (N), and phosphorus (P) dynamics during leaf litter decomposition, we investigated the temporal variability of soil microbial biomass and associated soil enzyme activities. Our 342-day leaf litter (Quercus wutaishanica) decomposition experiment at the Loess Plateau (China) sheds light on how soil microorganisms – mainly the soil microbial biomass C, N, P, and soil enzyme activities – maintain element homeostasis of C, N, and P by producing soil enzymes during various phases of litter decomposition. Overall, the highest soil enzyme activities were measured in summer, whereas soil microbial biomass carbon (MBC) and soil microbial biomass nitrogen (MBN) were highest in winter. Soil water content and soil temperature had significant effects on soil enzyme activities and stoichiometry. The results indicate that the stoichiometry of extracellular enzyme activities (lnBG:lnNAG:lnAP) changes significantly between individual stages of litter decomposition. The resources available for microorganisms were restricted by C and P, while P limitation progressively decelerated during decomposition and C limitation was enhanced at the latest stage. Strong positive correlations between ecological indicators of microbial element limitation and soil enzyme activities indicated that microbes allocate C and nutrients towards soil enzyme production to mine for scarce nutrients. This adaptation strategy enabled the soil microorganisms to maintain element homeostasis. Soil MBC, MBN, soil microbial biomass phosphorus (MBP), MBC:MBN, MBC:MBP, and MBN:MBP rarely showed significant correlations with soil or leaf litter C, N, P, C:N, C:P, and N:P. This suggests no resource dependency of microbial element composition but supports the concept of element homeostasis of soil microorganisms. Besides compensating for element imbalances by adjusting soil enzyme production, the microorganisms also adjusted element use efficiencies such as C use efficiency. We conclude that the maintenance of element homeostasis by soil microorganisms induces a tight co-regulation of enzymes involved in covering their C and nutrient supply during successive litter degradation.

Microbial mobilization of various P species depends on weathering history of soils

Microbial utilization of sugars in soil assessed by position-specific labeling and compound-specific 13C-PLFA-analysis

No abstract is provided for this article.

Contribution of arbuscular mycorrhiza and exoenzymes to nitrogen acquisition of sorghum under drought