Publications by authors named "Andreas Richter"

229 Publications

Ecological memory of recurrent drought modifies soil processes via changes in soil microbial community.

Nat Commun 2021 Sep 6;12(1):5308. Epub 2021 Sep 6.

Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria.

Climate change is altering the frequency and severity of drought events. Recent evidence indicates that drought may produce legacy effects on soil microbial communities. However, it is unclear whether precedent drought events lead to ecological memory formation, i.e., the capacity of past events to influence current ecosystem response trajectories. Here, we utilize a long-term field experiment in a mountain grassland in central Austria with an experimental layout comparing 10 years of recurrent drought events to a single drought event and ambient conditions. We show that recurrent droughts increase the dissimilarity of microbial communities compared to control and single drought events, and enhance soil multifunctionality during drought (calculated via measurements of potential enzymatic activities, soil nutrients, microbial biomass stoichiometry and belowground net primary productivity). Our results indicate that soil microbial community composition changes in concert with its functioning, with consequences for soil processes. The formation of ecological memory in soil under recurrent drought may enhance the resilience of ecosystem functioning against future drought events.
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http://dx.doi.org/10.1038/s41467-021-25675-4DOI Listing
September 2021

How can fertilization regimes and durations shape earthworm gut microbiota in a long-term field experiment?

Ecotoxicol Environ Saf 2021 Aug 16;224:112643. Epub 2021 Aug 16.

MOE Key Laboratory of Environment Remediation and Ecological Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, PR China; Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, PR China; State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, PR China.

The positive roles of earthworms on soil functionality has been extensively documented. The capacity of the earthworm gut microbiota on decomposition and nutrient cycling under long-term fertilization in field conditions has rarely been studied. Here, we report the structural, taxonomic, and functional responses of Eisenia foetida and Pheretima guillelmi gut microbiota to different fertilization regimes and durations using 16S rRNA gene-based Illumina sequencing and high-throughput quantitative PCR techniques. Our results revealed that the core gut microbiota, especially the fermentative bacteria were mainly sourced from the soil, but strongly stimulated with species-specificity, potential benefits for the host and soil health. The functional compositions of gut microbiota were altered by fertilization with fertilization duration being more influential than fertilization regimes. Moreover, the combination of organic and inorganic fertilization with the longer duration resulted in a higher richness and connectivity in the gut microbiota, and also their functional potential related to carbon (C), nitrogen, and phosphorus cycling, particularly the labile C decomposition, denitrification, and phosphate mobilization. We also found that long-term inorganic fertilization increased the abundance of pathogenic bacteria in the P. guillelmi gut. This study demonstrates that understanding earthworm gut microbiota can provide insights into how agricultural practices can potentially alter soil ecosystem functions through the interactions between soil and earthworm gut microbiotas.
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http://dx.doi.org/10.1016/j.ecoenv.2021.112643DOI Listing
August 2021

The effect of global change on soil phosphatase activity.

Glob Chang Biol 2021 Aug 12. Epub 2021 Aug 12.

CSIC, Global Ecology Unit CREAF-CSIC-UAB, Barcelona, Spain.

Soil phosphatase enzymes are produced by plant roots and microorganisms and play a key role in the cycling of phosphorus (P), an often-limiting element in terrestrial ecosystems. The production of these enzymes in soil is the most important biological strategy for acquiring phosphate ions from organic molecules. Previous works showed how soil potential phosphatase activity is mainly driven by climatic conditions and soil nitrogen (N) and carbon. Nonetheless, future trends of the activity of these enzymes under global change remain little known. We investigated the influence of some of the main drivers of change on soil phosphatase activity using a meta-analysis of results from 97 published studies. Our database included a compilation of N and P fertilization experiments, manipulation experiments with increased atmospheric CO concentration, warming, and drought, and studies comparing invaded and non-invaded ecosystems. Our results indicate that N fertilization leads to higher phosphatase activity, whereas P fertilization has the opposite effect. The rise of atmospheric CO levels or the arrival of invasive species also exhibits positive response ratios on the activity of soil phosphatases. However, the occurrence of recurrent drought episodes decreases the activity of soil phosphatases. Our analysis did not reveal statistically significant effects of warming on soil phosphatase activity. In general, soil enzymatic changes in the reviewed experiments depended on the initial nutrient and water status of the ecosystems. The observed patterns evidence that future soil phosphatase activity will not only depend on present-day soil conditions but also on potential compensations or amplifications among the different drivers of global change. The responses of soil phosphatases to the global change drivers reported in this study and the consideration of cost-benefit approaches based on the connection of the P and N cycle will be useful for a better estimation of phosphatase production in carbon (C)-N-P models.
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http://dx.doi.org/10.1111/gcb.15832DOI Listing
August 2021

Shifts in the Abundances of Saprotrophic and Ectomycorrhizal Fungi With Altered Leaf Litter Inputs.

Front Plant Sci 2021 21;12:682142. Epub 2021 Jul 21.

UFZ-Helmholtz Centre for Environmental Research, Department of Computational Hydrosystems, Leipzig, Germany.

Ectomycorrhizal (EcM) and saprotrophic fungi interact in the breakdown of organic matter, but the mechanisms underlying the EcM role on organic matter decomposition are not totally clear. We hypothesized that the ecological relations between EcM and saprotroph fungi are modulated by resources availability and accessibility, determining decomposition rates. We manipulated the amount of leaf litter inputs (No-Litter, Control Litter, Doubled Litter) on Trenched (root exclusion) and Non-Trenched plots (with roots) in a temperate deciduous forest of EcM-associated trees. Resultant shifts in soil fungal communities were determined by phospholipid fatty acids and DNA sequencing after 3 years, and CO fluxes were measured throughout this period. Different levels of leaf litter inputs generated a gradient of organic substrate availability and accessibility, altering the composition and ecological relations between EcM and saprotroph fungal communities. EcM fungi dominated at low levels of fresh organic substrates and lower organic matter quality, where short-distances exploration types seem to be better competitors, whereas saprotrophs and longer exploration types of EcM fungi tended to dominate at high levels of leaf litter inputs, where labile organic substrates were easily accessible. We were, however, not able to detect unequivocal signs of competition between these fungal groups for common resources. These results point to the relevance of substrate quality and availability as key factors determining the role of EcM and saprotroph fungi on litter and soil organic matter decay and represent a path forward on the capacity of organic matter decomposition of different exploration types of EcM fungi.
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http://dx.doi.org/10.3389/fpls.2021.682142DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8336600PMC
July 2021

Recently photoassimilated carbon and fungus-delivered nitrogen are spatially correlated in the ectomycorrhizal tissue of Fagus sylvatica.

New Phytol 2021 Jul 1. Epub 2021 Jul 1.

Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, A-1030, Austria.

Ectomycorrhizal plants trade plant-assimilated carbon for soil nutrients with their fungal partners. The underlying mechanisms, however, are not fully understood. Here we investigate the exchange of carbon for nitrogen in the ectomycorrhizal symbiosis of Fagus sylvatica across different spatial scales from the root system to the cellular level. We provided N-labelled nitrogen to mycorrhizal hyphae associated with one half of the root system of young beech trees, while exposing plants to a CO atmosphere. We analysed the short-term distribution of C and N in the root system with isotope-ratio mass spectrometry, and at the cellular scale within a mycorrhizal root tip with nanoscale secondary ion mass spectrometry (NanoSIMS). At the root system scale, plants did not allocate more C to root parts that received more N. Nanoscale secondary ion mass spectrometry imaging, however, revealed a highly heterogenous, and spatially significantly correlated distribution of C and N at the cellular scale. Our results indicate that, on a coarse scale, plants do not allocate a larger proportion of photoassimilated C to root parts associated with N-delivering ectomycorrhizal fungi. Within the ectomycorrhizal tissue, however, recently plant-assimilated C and fungus-delivered N were spatially strongly coupled. Here, NanoSIMS visualisation provides an initial insight into the regulation of ectomycorrhizal C and N exchange at the microscale.
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http://dx.doi.org/10.1111/nph.17591DOI Listing
July 2021

Genomic insights into diverse bacterial taxa that degrade extracellular DNA in marine sediments.

Nat Microbiol 2021 07 14;6(7):885-898. Epub 2021 Jun 14.

Division of Microbial Ecology, Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria.

Extracellular DNA is a major macromolecule in global element cycles, and is a particularly crucial phosphorus, nitrogen and carbon source for microorganisms in the seafloor. Nevertheless, the identities, ecophysiology and genetic features of DNA-foraging microorganisms in marine sediments are largely unknown. Here, we combined microcosm experiments, DNA stable isotope probing (SIP), single-cell SIP using nano-scale secondary isotope mass spectrometry (NanoSIMS) and genome-centric metagenomics to study microbial catabolism of DNA and its subcomponents in marine sediments. C-DNA added to sediment microcosms was largely degraded within 10 d and mineralized to CO. SIP probing of DNA revealed diverse 'Candidatus Izemoplasma', Lutibacter, Shewanella and Fusibacteraceae incorporated DNA-derived C-carbon. NanoSIMS confirmed incorporation of C into individual bacterial cells of Fusibacteraceae sorted from microcosms. Genomes of the C-labelled taxa all encoded enzymatic repertoires for catabolism of DNA or subcomponents of DNA. Comparative genomics indicated that diverse 'Candidatus Izemoplasmatales' (former Tenericutes) are exceptional because they encode multiple (up to five) predicted extracellular nucleases and are probably specialized DNA-degraders. Analyses of additional sediment metagenomes revealed extracellular nuclease genes are prevalent among Bacteroidota at diverse sites. Together, our results reveal the identities and functional properties of microorganisms that may contribute to the key ecosystem function of degrading and recycling DNA in the seabed.
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http://dx.doi.org/10.1038/s41564-021-00917-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8289736PMC
July 2021

Membrane integration into PDMS-free microfluidic platforms for organ-on-chip and analytical chemistry applications.

Lab Chip 2021 05;21(10):1866-1885

Department of Biomedical Science, Faculty of Medicine, Eberhard Karls University Tübingen, 72076 Tübingen, Germany. and NMI Natural and Medical Sciences Institute at the University of Tübingen, 72770 Reutlingen, Germany.

Membranes play a crucial role in many microfluidic systems, enabling versatile applications in highly diverse research fields. However, the tight and robust integration of membranes into microfluidic systems requires complex fabrication processes. Most integration approaches, so far, rely on polydimethylsiloxane (PDMS) as base material for the microfluidic chips. Several limitations of PDMS have resulted in the transition of many microfluidic approaches to PDMS-free systems using alternative materials such as thermoplastics. To integrate membranes in those PDMS-free systems, novel alternative approaches are required. This review provides an introduction into microfluidic systems applying membrane technology for analytical systems and organ-on-chip as well as a comprehensive overview of methods for the integration of membranes into PDMS-free systems. The overview and examples will provide a valuable resource and starting point for any researcher that is aiming at implementing membranes in microfluidic systems without using PDMS.
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http://dx.doi.org/10.1039/d1lc00188dDOI Listing
May 2021

Warming and elevated CO intensify drought and recovery responses of grassland carbon allocation to soil respiration.

Glob Chang Biol 2021 07 6;27(14):3230-3243. Epub 2021 May 6.

Department of Ecology, University of Innsbruck, Innsbruck, Austria.

Photosynthesis and soil respiration represent the two largest fluxes of CO in terrestrial ecosystems and are tightly linked through belowground carbon (C) allocation. Drought has been suggested to impact the allocation of recently assimilated C to soil respiration; however, it is largely unknown how drought effects are altered by a future warmer climate under elevated atmospheric CO (eT_eCO ). In a multifactor experiment on managed C3 grassland, we studied the individual and interactive effects of drought and eT_eCO (drought, eT_eCO , drought × eT_eCO ) on ecosystem C dynamics. We performed two in situ CO pulse-labeling campaigns to trace the fate of recent C during peak drought and recovery. eT_eCO increased soil respiration and the fraction of recently assimilated C in soil respiration. During drought, plant C uptake was reduced by c. 50% in both ambient and eT_eCO conditions. Soil respiration and the amount and proportion of C respired from soil were reduced (by 32%, 70% and 30%, respectively), the effect being more pronounced under eT_eCO (50%, 84%, 70%). Under drought, the diel coupling of photosynthesis and SR persisted only in the eT_eCO scenario, likely caused by dynamic shifts in the use of freshly assimilated C between storage and respiration. Drought did not affect the fraction of recent C remaining in plant biomass under ambient and eT_eCO , but reduced the small fraction remaining in soil under eT_eCO . After rewetting, C uptake and the proportion of recent C in soil respiration recovered more rapidly under eT_eCO compared to ambient conditions. Overall, our findings suggest that in a warmer climate under elevated CO drought effects on the fate of recent C will be amplified and the coupling of photosynthesis and soil respiration will be sustained. To predict the future dynamics of terrestrial C cycling, such interactive effects of multiple global change factors should be considered.
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http://dx.doi.org/10.1111/gcb.15628DOI Listing
July 2021

Empirical support for the biogeochemical niche hypothesis in forest trees.

Nat Ecol Evol 2021 02 4;5(2):184-194. Epub 2021 Jan 4.

CSIC, Global Ecology Unit CREAF-CEAB-UAB, Bellaterra, Spain.

The possibility of using the elemental compositions of species as a tool to identify species/genotype niche remains to be tested at a global scale. We investigated relationships between the foliar elemental compositions (elementomes) of trees at a global scale with phylogeny, climate, N deposition and soil traits. We analysed foliar N, P, K, Ca, Mg and S concentrations in 23,962 trees of 227 species. Shared ancestry explained 60-94% of the total variance in foliar nutrient concentrations and ratios whereas current climate, atmospheric N deposition and soil type together explained 1-7%, consistent with the biogeochemical niche hypothesis which predicts that each species will have a specific need for and use of each bio-element. The remaining variance was explained by the avoidance of nutritional competition with other species and natural variability within species. The biogeochemical niche hypothesis is thus able to quantify species-specific tree niches and their shifts in response to environmental changes.
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http://dx.doi.org/10.1038/s41559-020-01348-1DOI Listing
February 2021

Acclimation in plants - the Green Hub consortium.

Plant J 2021 04 31;106(1):23-40. Epub 2021 Jan 31.

Plant Molecular Biology, Faculty of Biology, Ludwig-Maximilians-Universität München, Planegg-Martinsried, 82152, Germany.

Acclimation is the capacity to adapt to environmental changes within the lifetime of an individual. This ability allows plants to cope with the continuous variation in ambient conditions to which they are exposed as sessile organisms. Because environmental changes and extremes are becoming even more pronounced due to the current period of climate change, enhancing the efficacy of plant acclimation is a promising strategy for mitigating the consequences of global warming on crop yields. At the cellular level, the chloroplast plays a central role in many acclimation responses, acting both as a sensor of environmental change and as a target of cellular acclimation responses. In this Perspective article, we outline the activities of the Green Hub consortium funded by the German Science Foundation. The main aim of this research collaboration is to understand and strategically modify the cellular networks that mediate plant acclimation to adverse environments, employing Arabidopsis, tobacco (Nicotiana tabacum) and Chlamydomonas as model organisms. These efforts will contribute to 'smart breeding' methods designed to create crop plants with improved acclimation properties. To this end, the model oilseed crop Camelina sativa is being used to test modulators of acclimation for their potential to enhance crop yield under adverse environmental conditions. Here we highlight the current state of research on the role of gene expression, metabolism and signalling in acclimation, with a focus on chloroplast-related processes. In addition, further approaches to uncovering acclimation mechanisms derived from systems and computational biology, as well as adaptive laboratory evolution with photosynthetic microbes, are highlighted.
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http://dx.doi.org/10.1111/tpj.15144DOI Listing
April 2021

Microbial growth and carbon use efficiency show seasonal responses in a multifactorial climate change experiment.

Commun Biol 2020 10 16;3(1):584. Epub 2020 Oct 16.

Terrestrial Ecosystem Research, Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria.

Microbial growth and carbon use efficiency (CUE) are central to the global carbon cycle, as microbial remains form soil organic matter. We investigated how future global changes may affect soil microbial growth, respiration, and CUE. We aimed to elucidate the soil microbial response to multiple climate change drivers across the growing season and whether effects of multiple global change drivers on soil microbial physiology are additive or interactive. We measured soil microbial growth, CUE, and respiration at three time points in a field experiment combining three levels of temperature and atmospheric CO, and a summer drought. Here we show that climate change-driven effects on soil microbial physiology are interactive and season-specific, while the coupled response of growth and respiration lead to stable microbial CUE (average CUE = 0.39). These results suggest that future research should focus on microbial growth across different seasons to understand and predict effects of global changes on soil carbon dynamics.
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http://dx.doi.org/10.1038/s42003-020-01317-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7567817PMC
October 2020

Acidobacteria are active and abundant members of diverse atmospheric H-oxidizing communities detected in temperate soils.

ISME J 2021 02 6;15(2):363-376. Epub 2020 Oct 6.

Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria.

Significant rates of atmospheric dihydrogen (H) consumption have been observed in temperate soils due to the activity of high-affinity enzymes, such as the group 1h [NiFe]-hydrogenase. We designed broadly inclusive primers targeting the large subunit gene (hhyL) of group 1h [NiFe]-hydrogenases for long-read sequencing to explore its taxonomic distribution across soils. This approach revealed a diverse collection of microorganisms harboring hhyL, including previously unknown groups and taxonomically not assignable sequences. Acidobacterial group 1h [NiFe]-hydrogenase genes were abundant and expressed in temperate soils. To support the participation of acidobacteria in H consumption, we studied two representative mesophilic soil acidobacteria, which expressed group 1h [NiFe]-hydrogenases and consumed atmospheric H during carbon starvation. This is the first time mesophilic acidobacteria, which are abundant in ubiquitous temperate soils, have been shown to oxidize H down to below atmospheric concentrations. As this physiology allows bacteria to survive periods of carbon starvation, it could explain the success of soil acidobacteria. With our long-read sequencing approach of group 1h [NiFe]-hydrogenase genes, we show that the ability to oxidize atmospheric levels of H is more widely distributed among soil bacteria than previously recognized and could represent a common mechanism enabling bacteria to persist during periods of carbon deprivation.
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http://dx.doi.org/10.1038/s41396-020-00750-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8027828PMC
February 2021

Covid-19: implications for insurer risk management and the insurability of pandemic risk.

Geneva Risk Insur Rev 2020 Sep 22:1-29. Epub 2020 Sep 22.

Ludwig-Maximilians-Universität München (LMU Munich), Munich, Germany.

This paper analyzes the insurability of pandemic risk and outlines how underwriting policies and scenario analysis are used to build resilience upfront and plan contingency actions for crisis scenarios. It then summarizes the unique "lessons learned" from the Covid-19 crisis by baselining actual developments against a reasonable, pre-Covid-19 pandemic scenario based on the 2002 SARS epidemic and 1918 Spanish influenza pandemic. Actual developments support the pre-Covid-19 hypothesis that financial market developments dominate claims losses due to the demographics of pandemics and other factors. However, Covid-19 "surprised" relative to the pre-Covid-19 scenario in terms of its impact on the real economy as well as on the property and casualty segment as business interruption property triggers and exclusions are challenged, something that may adversely impact the insurability of pandemics as well as the perception of the industry for some time to come. The unique lessons of Covid-19 reinforce the need for resilience upfront in solvency and liquidity, the need to improve business interruption wordings and re-underwrite the book, and the recognition that business interruption caused by pandemics may not be an insurable risk due to its large accumulation potential and the threat of external moral hazard. These insurability limitations lead to a discussion about the structure and financing of protection against the impact of future pandemics.
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http://dx.doi.org/10.1057/s10713-020-00054-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7506824PMC
September 2020

Composition and activity of nitrifier communities in soil are unresponsive to elevated temperature and CO, but strongly affected by drought.

ISME J 2020 12 7;14(12):3038-3053. Epub 2020 Aug 7.

Centre for Microbiology and Environmental Systems Science, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria.

Nitrification is a fundamental process in terrestrial nitrogen cycling. However, detailed information on how climate change affects the structure of nitrifier communities is lacking, specifically from experiments in which multiple climate change factors are manipulated simultaneously. Consequently, our ability to predict how soil nitrogen (N) cycling will change in a future climate is limited. We conducted a field experiment in a managed grassland and simultaneously tested the effects of elevated atmospheric CO, temperature, and drought on the abundance of active ammonia-oxidizing bacteria (AOB) and archaea (AOA), comammox (CMX) Nitrospira, and nitrite-oxidizing bacteria (NOB), and on gross mineralization and nitrification rates. We found that N transformation processes, as well as gene and transcript abundances, and nitrifier community composition were remarkably resistant to individual and interactive effects of elevated CO and temperature. During drought however, process rates were increased or at least maintained. At the same time, the abundance of active AOB increased probably due to higher NH availability. Both, AOA and comammox Nitrospira decreased in response to drought and the active community composition of AOA and NOB was also significantly affected. In summary, our findings suggest that warming and elevated CO have only minor effects on nitrifier communities and soil biogeochemical variables in managed grasslands, whereas drought favors AOB and increases nitrification rates. This highlights the overriding importance of drought as a global change driver impacting on soil microbial community structure and its consequences for N cycling.
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http://dx.doi.org/10.1038/s41396-020-00735-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7784676PMC
December 2020

Regulation of nitrogen fixation from free-living organisms in soil and leaf litter of two tropical forests of the Guiana shield.

Plant Soil 2020 1;450(1):93-110. Epub 2019 Apr 1.

Centre of Excellence PLECO (Plants and Ecosystems), Department of Biology, University of Antwerp, Wilrijk, Belgium.

Background And Aims: Biological fixation of atmospheric nitrogen (N) is the main pathway for introducing N into unmanaged ecosystems. While recent estimates suggest that free-living N fixation (FLNF) accounts for the majority of N fixed in mature tropical forests, the controls governing this process are not completely understood. The aim of this study was to quantify FLNF rates and determine its drivers in two tropical pristine forests of French Guiana.

Methods: We used the acetylene reduction assay to measure FLNF rates at two sites, in two seasons and along three topographical positions, and used regression analyses to identify which edaphic explanatory variables, including carbon (C), nitrogen (N), phosphorus (P) and molybdenum (Mo) content, pH, water and available N and P, explained most of the variation in FLNF rates.

Results: Overall, FLNF rates were lower than measured in tropical systems elsewhere. In soils seasonal variability was small and FLNF rates differed among topographies at only one site. Water, P and pH explained 24% of the variation. In leaf litter, FLNF rates differed seasonally, without site or topographical differences. Water, C, N and P explained 46% of the observed variation. We found no regulatory role of Mo at our sites.

Conclusions: Rates of FLNF were low in primary rainforest on poor soils on the Guiana shield. Water was the most important rate-regulating factor and FLNF increased with increasing P, but decreased with increasing N. Our results support the general assumption that N fixation in tropical lowland forests is limited by P availability.
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http://dx.doi.org/10.1007/s11104-019-04012-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7319290PMC
April 2019

Hydrogel Patterns in Microfluidic Devices by Do-It-Yourself UV-Photolithography Suitable for Very Large-Scale Integration.

Micromachines (Basel) 2020 May 2;11(5). Epub 2020 May 2.

Institut für Halbleiter- und Mikrosystemtechnik, Technische Universität Dresden, 01187 Dresden, Germany.

The interest in large-scale integrated (LSI) microfluidic systems that perform high-throughput biological and chemical laboratory investigations on a single chip is steadily growing. Such highly integrated Labs-on-a-Chip (LoC) provide fast analysis, high functionality, outstanding reproducibility at low cost per sample, and small demand of reagents. One LoC platform technology capable of LSI relies on specific intrinsically active polymers, the so-called stimuli-responsive hydrogels. Analogous to microelectronics, the active components of the chips can be realized by photolithographic micro-patterning of functional layers. The miniaturization potential and the integration degree of the microfluidic circuits depend on the capability of the photolithographic process to pattern hydrogel layers with high resolution, and they typically require expensive cleanroom equipment. Here, we propose, compare, and discuss a cost-efficient do-it-yourself (DIY) photolithographic set-up suitable to micro-pattern hydrogel-layers with a resolution as needed for very large-scale integrated (VLSI) microfluidics. The achievable structure dimensions are in the lower micrometer scale, down to a feature size of 20 µm with aspect ratios of 1:5 and maximum integration densities of 20,000 hydrogel patterns per cm². Furthermore, we demonstrate the effects of miniaturization on the efficiency of a hydrogel-based microreactor system by increasing the surface area to volume (SA:V) ratio of integrated bioactive hydrogels. We then determine and discuss a correlation between ultraviolet (UV) exposure time, cross-linking density of polymers, and the degree of immobilization of bioactive components.
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http://dx.doi.org/10.3390/mi11050479DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7281684PMC
May 2020

The -dependent signalling pathway coordinates plastid biogenesis with the synthesis of anthocyanins.

Philos Trans R Soc Lond B Biol Sci 2020 06 4;375(1801):20190403. Epub 2020 May 4.

Plant Physiology, Institute of Biology, Humboldt-Universität zu Berlin, Philippstrasse 13, 10115 Berlin, Germany.

In recent years, it has become evident that plants perceive, integrate and communicate abiotic stress signals through chloroplasts. During the process of acclimation plastid-derived, retrograde signals control nuclear gene expression in response to developmental and environmental cues leading to complex genetic and metabolic reprogramming to preserve cellular homeostasis under challenging environmental conditions. Upon stress-induced dysfunction of chloroplasts, GENOMES UNCOUPLED (GUN) proteins participate in the repression of (s). Here, we show that the retrograde signal emitted by, or communicated through, GUN-proteins is also essential to induce the accumulation of photoprotective anthocyanin pigments when chloroplast development is attenuated. Comparative whole transcriptome sequencing and genetic analysis reveal GUN1 and GUN5-dependent signals as a source for the regulation of genes involved in anthocyanin biosynthesis. The signal transduction cascade includes well-known transcription factors for the control of anthocyanin biosynthesis, which are deregulated in mutants. We propose that regulation of and genes contributing to anthocyanin biosynthesis are two, albeit oppositely, co-regulated processes during plastid biogenesis. This article is part of the theme issue 'Retrograde signalling from endosymbiotic organelles'.
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http://dx.doi.org/10.1098/rstb.2019.0403DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7209955PMC
June 2020

Post-translational coordination of chlorophyll biosynthesis and breakdown by BCMs maintains chlorophyll homeostasis during leaf development.

Nat Commun 2020 03 20;11(1):1254. Epub 2020 Mar 20.

Institute of Biology/Plant Physiology, Humboldt-Universität zu Berlin, Philippstraße 13, 10115, Berlin, Germany.

Chlorophyll is indispensable for life on Earth. Dynamic control of chlorophyll level, determined by the relative rates of chlorophyll anabolism and catabolism, ensures optimal photosynthesis and plant fitness. How plants post-translationally coordinate these two antagonistic pathways during their lifespan remains enigmatic. Here, we show that two Arabidopsis paralogs of BALANCE of CHLOROPHYLL METABOLISM (BCM) act as functionally conserved scaffold proteins to regulate the trade-off between chlorophyll synthesis and breakdown. During early leaf development, BCM1 interacts with GENOMES UNCOUPLED 4 to stimulate Mg-chelatase activity, thus optimizing chlorophyll synthesis. Meanwhile, BCM1's interaction with Mg-dechelatase promotes degradation of the latter, thereby preventing chlorophyll degradation. At the onset of leaf senescence, BCM2 is up-regulated relative to BCM1, and plays a conserved role in attenuating chlorophyll degradation. These results support a model in which post-translational regulators promote chlorophyll homeostasis by adjusting the balance between chlorophyll biosynthesis and breakdown during leaf development.
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http://dx.doi.org/10.1038/s41467-020-14992-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7083845PMC
March 2020

Hydrogel Microvalves as Control Elements for Parallelized Enzymatic Cascade Reactions in Microfluidics.

Micromachines (Basel) 2020 Feb 5;11(2). Epub 2020 Feb 5.

Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Straße 6, 01069 Dresden, Germany.

Compartmentalized microfluidic devices with immobilized catalysts are a valuable tool for overcoming the incompatibility challenge in (bio) catalytic cascade reactions and high-throughput screening of multiple reaction parameters. To achieve flow control in microfluidics, stimuli-responsive hydrogel microvalves were previously introduced. However, an application of this valve concept for the control of multistep reactions was not yet shown. To fill this gap, we show the integration of thermoresponsive poly(-isopropylacrylamide) (PNiPAAm) microvalves (diameter: 500 and 600 µm) into PDMS-on-glass microfluidic devices for the control of parallelized enzyme-catalyzed cascade reactions. As a proof-of-principle, the biocatalysts glucose oxidase (GOx), horseradish peroxidase (HRP) and myoglobin (Myo) were immobilized in photopatterned hydrogel dot arrays (diameter of the dots: 350 µm, amount of enzymes: 0.13-2.3 µg) within three compartments of the device. Switching of the microvalves was achieved within 4 to 6 s and thereby the fluid pathway of the enzyme substrate solution (5 mmol/L) in the device was determined. Consequently, either the enzyme cascade reaction GOx-HRP or GOx-Myo was performed and continuously quantified by ultraviolet-visible (UV-Vis) spectroscopy. The functionality of the microvalves was shown in four hourly switching cycles and visualized by the path-dependent substrate conversion.
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http://dx.doi.org/10.3390/mi11020167DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7074747PMC
February 2020

Response of human periosteal cells to degradation products of zinc and its alloy.

Mater Sci Eng C Mater Biol Appl 2020 Mar 31;108:110208. Epub 2019 Oct 31.

Department of Oral and Maxillofacial Surgery, University Hospital Tübingen, Osianderstrasse 2-8, Tübingen, 72076, Germany. Electronic address:

Zinc (Zn) and its alloys are proposed as promising resorbable materials for osteosynthesis implants. Detailed studies should be undertaken to clarify their properties in terms of degradability, biocompatibility and osteoinductivity. Degradation products of Zn alloys might affect directly adjacent cellular and tissue responses. Periosteal stem cells are responsible for participating in intramembranous ossification during fracture healing. The present study aims at examining possible effects emanating from Zn or Zn-4Ag (wt%) alloy degradation products on cell viability and osteogenic differentiation of a human immortalized cranial periosteal cell line (TAg cells). Therefore, a modified extraction method was used to investigate the degradation behavior of Zn and Zn-4Ag alloys under cell culture conditions. Compared with pure Zn, Zn-4Ag alloy showed almost fourfold higher degradation rates under cell culture conditions, while the associated degradation products had no adverse effects on cell viability. Osteogenic induction of TAg cells revealed that high concentration extracts significantly reduced calcium deposition of TAg cells, while low concentration extracts enhanced calcium deposition, indicating a dose-dependent effect of Zn ions. Our results give evidence that the observed cytotoxicity effects were determined by the released degradation products of Zn and Zn-4Ag alloys, rather than by degradation rates calculated by weight loss. Extracellular Zn ion concentration was found to modulate osteogenic differentiation of TAg cells. These findings provide significant implications and guidance for the development of Zn-based alloys with an optimized degradation behavior for Zn-based osteosynthesis implants.
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http://dx.doi.org/10.1016/j.msec.2019.110208DOI Listing
March 2020

Evaluation of a Zn-2Ag-1.8Au-0.2V Alloy for Absorbable Biocompatible Materials.

Materials (Basel) 2019 Dec 20;13(1). Epub 2019 Dec 20.

Section Medical Materials Science and Technology, University Hospital Tübingen, Osianderstrasse 2-8, 72076 Tübingen, Germany.

Zinc (Zn) and Zn-based alloys have been proposed as a new generation of absorbable metals mainly owing to the moderate degradation behavior of zinc between magnesium and iron. Nonetheless, mechanical strength of pure Zn is relatively poor, making it insufficient for the majority of clinical applications. In this study, a novel Zn-2Ag-1.8Au-0.2V (wt.%) alloy (Zn-Ag-Au-V) was fabricated and investigated for use as a potential absorbable biocompatible material. Microstructural characterization indicated an effective grain-refining effect on the Zn alloy after a thermomechanical treatment. Compared to pure Zn, the Zn-Ag-Au-V alloy showed significantly enhanced mechanical properties, with a yield strength of 168 MPa, an ultimate tensile strength of 233 MPa, and an elongation of 17%. Immersion test indicated that the degradation rate of the Zn-Ag-Au-V alloy in Dulbecco's phosphate buffered saline was approximately 7.34 ± 0.64 μm/year, thus being slightly lower than that of pure Zn. Biocompatibility tests with L929 and Saos-2 cells showed a moderate cytotoxicity, alloy extracts at 16.7%, and 10% concentration did not affect metabolic activity and cell proliferation. Plaque formation in vitro was reduced, the Zn-Ag-Au-V surface inhibited adhesion and biofilm formation by the early oral colonizer , indicating antibacterial properties of the alloy.
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http://dx.doi.org/10.3390/ma13010056DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6981962PMC
December 2019

Microbial carbon limitation: The need for integrating microorganisms into our understanding of ecosystem carbon cycling.

Glob Chang Biol 2019 Dec 14. Epub 2019 Dec 14.

Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria.

Numerous studies have demonstrated that fertilization with nutrients such as nitrogen, phosphorus, and potassium increases plant productivity in both natural and managed ecosystems, demonstrating that primary productivity is nutrient limited in most terrestrial ecosystems. In contrast, it has been demonstrated that heterotrophic microbial communities in soil are primarily limited by organic carbon or energy. While this concept of contrasting limitations, that is, microbial carbon and plant nutrient limitation, is based on strong evidence that we review in this paper, it is often ignored in discussions of ecosystem response to global environment changes. The plant-centric perspective has equated plant nutrient limitations with those of whole ecosystems, thereby ignoring the important role of the heterotrophs responsible for soil decomposition in driving ecosystem carbon storage. To truly integrate carbon and nutrient cycles in ecosystem science, we must account for the fact that while plant productivity may be nutrient limited, the secondary productivity by heterotrophic communities is inherently carbon limited. Ecosystem carbon cycling integrates the independent physiological responses of its individual components, as well as tightly coupled exchanges between autotrophs and heterotrophs. To the extent that the interacting autotrophic and heterotrophic processes are controlled by organisms that are limited by nutrient versus carbon accessibility, respectively, we propose that ecosystems by definition cannot be 'limited' by nutrients or carbon alone. Here, we outline how models aimed at predicting non-steady state ecosystem responses over time can benefit from dissecting ecosystems into the organismal components and their inherent limitations to better represent plant-microbe interactions in coupled carbon and nutrient models.
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http://dx.doi.org/10.1111/gcb.14962DOI Listing
December 2019

A systemic overreaction to years versus decades of warming in a subarctic grassland ecosystem.

Nat Ecol Evol 2020 01 9;4(1):101-108. Epub 2019 Dec 9.

Department of Biology, University of Antwerp, Wilrijk, Belgium.

Temperature governs most biotic processes, yet we know little about how warming affects whole ecosystems. Here we examined the responses of 128 components of a subarctic grassland to either 5-8 or >50 years of soil warming. Warming of >50 years drove the ecosystem to a new steady state possessing a distinct biotic composition and reduced species richness, biomass and soil organic matter. However, the warmed state was preceded by an overreaction to warming, which was related to organism physiology and was evident after 5-8 years. Ignoring this overreaction yielded errors of >100% for 83 variables when predicting their responses to a realistic warming scenario of 1 °C over 50 years, although some, including soil carbon content, remained stable after 5-8 years. This study challenges long-term ecosystem predictions made from short-term observations, and provides a framework for characterization of ecosystem responses to sustained climate change.
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http://dx.doi.org/10.1038/s41559-019-1055-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6942924PMC
January 2020

Enhanced structural maturation of human induced pluripotent stem cell-derived cardiomyocytes under a controlled microenvironment in a microfluidic system.

Acta Biomater 2020 01 26;102:273-286. Epub 2019 Nov 26.

Institute of Pharmacology and Toxicology, Technische Universität Dresden, Fetscherstr. 74, 01307 Dresden, Germany. Electronic address:

The lack of a fully developed human cardiac model in vitro hampers the progress of many biomedical research fields including pharmacology, developmental biology, and disease modeling. Currently, available methods may only differentiate human induced pluripotent stem cells (iPSCs) into immature cardiomyocytes. To achieve cardiomyocyte maturation, appropriate modulation of cellular microenvironment is needed. This study aims to optimize a microfluidic system that enhances maturation of human iPSC-derived cardiomyocytes (iPSC-CMs) through cyclic pulsatile hemodynamic forces. Human iPSC-CMs cultured in the microfluidic system show increased alignment and contractility and appear more rod-like shaped with increased cell size and increased sarcomere length when compared to static cultures. Increased complexity and density of the mitochondrial network in iPSC-CMs cultured in the microfluidic system are in line with expression of mitochondrial marker genes MT-CO1 and OPA1. Moreover, the optimized microfluidic system is capable of stably maintaining controlled oxygen levels and inducing hypoxia, revealed by increased expression of HIF1α and EGLN2 as well as changes in contraction parameters in iPSC-CMs. In summary, this microfluidic system boosts the structural maturation of iPSC-CM culture and could serve as an advanced in vitro cardiac model for biomedical research in the future. STATEMENT OF SIGNIFICANCE: The availability of in vitro human cardiomyocytes generated from induced pluripotent stem cells (iPSCs) opens the possibility to develop human in vitro heart models for disease modeling and drug testing. However, iPSC-derived cardiomyocytes remain structurally and functionally immature, which hinders their application. In this manuscript, we present an optimized and complete microfluidic system that enhances maturation of iPSC-derived cardiomyocytes through physiological cyclic pulsatile hemodynamic forces. Furthermore, we improved our microfluidic system by using a closed microfluidic recirculation and oxygen exchangers to achieve and maintain low oxygen in the culture chambers, which is suitable for mimicking the hypoxic condition and studying the pathophysiological mechanisms of human diseases in vitro. In the future, a variety of technologies including 3D tissue engineering could be integrated into our system, which may greatly extend the use of iPSC-derived cardiac models in drug development and disease modeling.
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http://dx.doi.org/10.1016/j.actbio.2019.11.044DOI Listing
January 2020

Association between true non-contrast and virtual non-contrast vertebral bone CT attenuation values determined using dual-layer spectral detector CT.

Eur J Radiol 2019 Dec 7;121:108740. Epub 2019 Nov 7.

Department of Diagnostic and Interventional Radiology, Heidelberg University Hospital, INF 110, 69120, Heidelberg, Germany. Electronic address:

Purpose: To investigate the association of vertebral CT attenuation between virtual non-contrast (VNC) and true non-contrast (TNC) images and to evaluate if VNC vertebral CT attenuation could be used for phantom-less osteoporosis detection in dual-layer spectral-detector CT (SDCT).

Methods: 200 patients with non-contrast and portal-venous phase SDCT were retrospectively assigned to a test and a validation group of 100 patients each. CT attenuation of L1 vertebrae were measured on VNC and TNC. The test group was used to determine the difference between VNC and TNC CT attenuation and to calculate a statistical model for TNC CT attenuation prediction. The validation group was used to assess the capability of the model to predict TNC from VNC CT attenuation and its accuracy to identify osteoporosis. Osteoporosis was defined as a TNC CT attenuation of ≤110HU.

Results: In both groups, CT attenuation was lower in VNC than in TNC (P < 0.001). VNC and TNC CT attenuation was correlated strongly (r = 0.958). Using the regression equation established in the test group (TNC = 23.677 + 1.540 × VNC), the predicted TNC CT attenuation did not differ from the real TNC CT attenuation in the validation group (P = 0.359). A VNC CT attenuation cut-off of 52HU yielded an AUC of 0.978 for osteoporosis detection.

Conclusions: L1 CT attenuation is systematically underestimated in VNC compared with TNC images. However, TNC L1 CT attenuation can be predicted reliably from VNC. VNC may perform well in phantom-less osteoporosis detection.
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http://dx.doi.org/10.1016/j.ejrad.2019.108740DOI Listing
December 2019

Soil multifunctionality is affected by the soil environment and by microbial community composition and diversity.

Soil Biol Biochem 2019 Sep 26;136:107521. Epub 2019 Jun 26.

University of Vienna, Center for Microbiology and Environmental Systems Science, Department of Microbiology and Ecosystem Science, Division of Terrestrial Ecosystem Research, Althanstrasse 14, 1090 Vienna, Austria.

Microorganisms are critical in mediating carbon (C) and nitrogen (N) cycling processes in soils. Yet, it has long been debated whether the processes underlying biogeochemical cycles are affected by the composition and diversity of the soil microbial community or not. The composition and diversity of soil microbial communities can be influenced by various environmental factors, which in turn are known to impact biogeochemical processes. The objectives of this study were to test effects of multiple edaphic drivers individually and represented as the multivariate soil environment interacting with microbial community composition and diversity, and concomitantly on multiple soil functions (i.e. soil enzyme activities, soil C and N processes). We employed high-throughput sequencing (Illumina MiSeq) to analyze bacterial/archaeal and fungal community composition by targeting the 16S rRNA gene and the ITS1 region of soils collected from three land uses (cropland, grassland and forest) deriving from two bedrock forms (silicate and limestone). Based on this data set we explored single and combined effects of edaphic variables on soil microbial community structure and diversity, as well as on soil enzyme activities and several soil C and N processes. We found that both bacterial/archaeal and fungal communities were shaped by the same edaphic factors, with most single edaphic variables and the combined soil environment representation exerting stronger effects on bacterial/archaeal communities than on fungal communities, as demonstrated by (partial) Mantel tests. We also found similar edaphic controls on the bacterial/archaeal/fungal richness and diversity. Soil C processes were only directly affected by the soil environment but not affected by microbial community composition. In contrast, soil N processes were significantly related to bacterial/archaeal community composition and bacterial/archaeal/fungal richness/diversity but not directly affected by the soil environment. This indicates direct control of the soil environment on soil C processes and indirect control of the soil environment on soil N processes by structuring the microbial communities. The study further highlights the importance of edaphic drivers and microbial communities (i.e. composition and diversity) on important soil C and N processes.
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http://dx.doi.org/10.1016/j.soilbio.2019.107521DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6837881PMC
September 2019

Growth explains microbial carbon use efficiency across soils differing in land use and geology.

Soil Biol Biochem 2019 Jan 15;128:45-55. Epub 2018 Oct 15.

Department of Microbiology and Ecosystem Science, Research Network "Chemistry Meets Microbiology", University of Vienna, Althanstraße 14, 1090 Vienna, Austria.

The ratio of carbon (C) that is invested into microbial growth to organic C taken up is known as microbial carbon use efficiency (CUE), which is influenced by environmental factors such as soil temperature and soil moisture. How microbes will physiologically react to short-term environmental changes is not well understood, primarily due to methodological restrictions. Here we report on two independent laboratory experiments to explore short-term temperature and soil moisture effects on soil microbial physiology (i.e. respiration, growth, CUE, and microbial biomass turnover): (i) a temperature experiment with 1-day pre-incubation at 5, 15 and 25 °C at 60% water holding capacity (WHC), and (ii) a soil moisture/oxygen (O) experiment with 7-day pre-incubation at 20 °C at 30%, 60% WHC (both at 21% O) and 90% WHC at 1% O. Experiments were conducted with soils from arable, pasture and forest sites derived from both silicate and limestone bedrocks. We found that microbial CUE responded heterogeneously though overall positively to short-term temperature changes, and decreased significantly under high moisture level (90% WHC)/suboxic conditions due to strong decreases in microbial growth. Microbial biomass turnover time decreased dramatically with increasing temperature, and increased significantly at high moisture level (90% WHC)/suboxic conditions. Our findings reveal that the responses of microbial CUE and microbial biomass turnover to short-term temperature and moisture/O changes depended mainly on microbial growth responses and less on respiration responses to the environmental cues, which were consistent across soils differing in land use and geology.
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http://dx.doi.org/10.1016/j.soilbio.2018.10.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6774786PMC
January 2019

Plant roots increase both decomposition and stable organic matter formation in boreal forest soil.

Nat Commun 2019 09 4;10(1):3982. Epub 2019 Sep 4.

Department of Agricultural Sciences, University of Helsinki, PO Box 66, Helsinki, Finland.

Boreal forests are ecosystems with low nitrogen (N) availability that store globally significant amounts of carbon (C), mainly in plant biomass and soil organic matter (SOM). Although crucial for future climate change predictions, the mechanisms controlling boreal C and N pools are not well understood. Here, using a three-year field experiment, we compare SOM decomposition and stabilization in the presence of roots, with exclusion of roots but presence of fungal hyphae and with exclusion of both roots and fungal hyphae. Roots accelerate SOM decomposition compared to the root exclusion treatments, but also promote a different soil N economy with higher concentrations of organic soil N compared to inorganic soil N accompanied with the build-up of stable SOM-N. In contrast, root exclusion leads to an inorganic soil N economy (i.e., high level of inorganic N) with reduced stable SOM-N build-up. Based on our findings, we provide a framework on how plant roots affect SOM decomposition and stabilization.
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http://dx.doi.org/10.1038/s41467-019-11993-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6726645PMC
September 2019

Nutrient scarcity strengthens soil fauna control over leaf litter decomposition in tropical rainforests.

Proc Biol Sci 2019 09 4;286(1910):20191300. Epub 2019 Sep 4.

CSIC, Global Ecology Unit CREAF-CSIC-UAB, 08913 Bellaterra, Spain.

Soil fauna is a key control of the decomposition rate of leaf litter, yet its interactions with litter quality and the soil environment remain elusive. We conducted a litter decomposition experiment across different topographic levels within the landscape replicated in two rainforest sites providing natural gradients in soil fertility to test the hypothesis that low nutrient availability in litter and soil increases the strength of fauna control over litter decomposition. We crossed these data with a large dataset of 44 variables characterizing the biotic and abiotic microenvironment of each sampling point and found that microbe-driven carbon (C) and nitrogen (N) losses from leaf litter were 10.1 and 17.9% lower, respectively, in the nutrient-poorest site, but this among-site difference was equalized when meso- and macrofauna had access to the litterbags. Further, on average, soil fauna enhanced the rate of litter decomposition by 22.6%, and this contribution consistently increased as nutrient availability in the microenvironment declined. Our results indicate that nutrient scarcity increases the importance of soil fauna on C and N cycling in tropical rainforests. Further, soil fauna is able to equalize differences in microbial decomposition potential, thus buffering to a remarkable extent nutrient shortages at an ecosystem level.
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http://dx.doi.org/10.1098/rspb.2019.1300DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6742996PMC
September 2019
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