Publications

Background: Increasing drought frequency poses a significant threat to agricultural productivity. A promising strategy to enhance crop resilience against drought is the utilisation of root channels left by winter cover crops, which can improve access to subsoil water and nutrients for subsequent cash crops like maize (Zea mays L.). The impact of drought on bacterial communities inhabiting these root channels remains largely unknown. Here, we investigated drought-induced shifts in maize rhizosphere bacterial communities and their functional adaptation in cover crop root channels across three soil types in northern Germany (Luvisol, Podzol, and Phaeozem). Results: Using a multi-omics approach (16S rRNA gene amplicon sequencing, qPCR, and metaproteomics), we identified significant taxonomic and functional responses to drought. A rise in the abundance of K-strategist bacterial communities indicate a shift towards stress-tolerant populations with drought. Under drought stress, the relative abundances of Acidobacteriota, Actinomycetota, Planctomycetota, and Pseudomonadota increased, while Chloroflexota, Methylomirabilota, Ca. Patescibacteria, and Verrucomicrobiota declined. Functional analyses revealed that drought-stressed aerobic taxa among the Pseudomonadota and Verrucomicrobiota upregulated the glyoxylate cycle, potentially enhancing carbon and energy conservation, and increased antioxidant defences (catalase-glutathione peroxidase and methionine cycle-transsulfuration pathway). These drought-mitigating strategies were especially pronounced in root channels formed by Brassicaceae and Poaceae cover crops in the Luvisol and Podzol soils. Conclusions: These findings demonstrate the functional plasticity of rhizosphere bacterial communities in reused root channels in response to drought, highlighting the potential to leverage microbiome-mediated resilience for agricultural practices.

Rising global stoichiometric imbalance between increasing nitrogen (N) availability and depleting phosphorus (P) resources increases the importance of soil microbial P recycling. The contribution of extra- versus intracellular P (re-)cycling depending on ecosystem nutrient status is vastly unclear, making soil microorganisms a blind spot in our understanding of ecosystem responses to increasing P deficiency. We quantified P incorporation into microbial DNA and phospholipids by 33P labeling under contrasting conditions: low/high P soil × low/high carbon (C)NP application. By combining 33P and 14C labeling with tracing of microbial community biomarkers and functional genes, we disengaged the role of DNA and phospholipids in soil P cycling. Microorganisms in low P soil preferentially allocated P to phospholipids with an acceleration of phospholipids metabolism driven by C addition, which was strongly related to high abundances of microbial community members (e.g. some G-) with a fast phospholipids turnover. In high P soil, however, more P was allocated to DNA with a microbial functional shift towards DNA synthesis to support a replicative growth when sufficient C was supplied, which was coupled with a strong enrichment of fungal copiotrophs and microbial genes coding DNA primase. Consequently, adaptation to low P availability accelerated microbial intracellular P recycling through reutilization of the P stored in phospholipids. However, microorganisms under high P availability commonly adopted extracellular P recycling with release and reuse of DNA P by microbial death-growth dynamics. These results advance our understanding on microbial adaptation to P deficiency in soil by regulating component-specific P pathways and reflect the specific functions of phospholipids and DNA for P recycling.

The mobilization of soil nutrients bound in organic matter is largely mediated by enzymes derived from plants, soil microorganisms and animal residues. Land-use change alters important soil characteristics that may affect the activities of soil enzymes. However, mechanistic understanding of how land use and management practices influence the catalytic properties of enzymes in top- and subsoil are still scarce, especially in African ecosystems. We linked catalytic properties i.e. substrate affinity constant (Km) and maximum reaction rate (Vmax), determined by Michaelis–Menten kinetics, to a set of environmental and microbial variables in the soils of a land-use sequence (6 ecosystems) ranging from natural forests to agricultural fields at Mt. Kilimanjaro. The sensitivity of Km and Vmax of four extracellular hydrolytical enzymes, β-galactosidase, cellobiohydrolase, phosphatase and chitinase to changing environmental conditions were tested by fluorogenic substrates in topsoils and subsoils. The β-galactosidase activity increased with increasing soil depth. Other extracellular enzyme (cellobiohydrolase, phosphatase and chitinase) activities decreased with depth. The affinity of enzymes to substrates was higher in soils of natural compared to agricultural ecosystems: i.e. higher under forests than under cropland. The activity of β-galactosidase, cellobiohydrolase and chitinase enzyme were highest in lower mountain forest and grassland (less disturbed ecosystems). This indicated that changes in land use and management practice not only affects enzyme activity but also controls enzyme kinetics (Km and Ka) thus pointing towards the expression of different enzyme systems. Therefore, we concluded that anthropogenic activities result in alteration of C and nutrient cycling by affecting microbial activities and enzymes catalytic properties.

Comparing the belowground allocation of assimilated carbon (C) to roots and mycorrhizal fungi across biomes can reveal specific plant nutrient acquisition strategies in ecosystems and allows to predict consequences of environmental changes. Three natural ecosystems (arid shrubland, coastal matorral, humid-temperate forest) distinct in annual precipitation and vegetation cover and compositions were selected to conduct a 13CO2 pulse labeling of natural woody vegetation to chase the allocation of assimilated C to arbuscular mycorrhizal (AM) fungi and fine roots. Further, nitrogen (N) and phosphorus (P) availability, root traits, root colonization, and the extraradical AM fungal mycelium (PLFA and NLFA 16:1ω5c) were analyzed to evaluate the efficiency of nutrient acquisition strategies. AM fungal colonization decreased with increasing aridity by up to 55% intraradical and by up to 90% extraradical. High root tissue densities – indicating longevity of roots – and low specific root lengths – indicating a low nutrient uptake capacity – pointed to a slow and resource conservative acquisition strategy of plants in the arid shrubland. Plants in the matorral, on the contrary, had lower root tissue densities but higher specific root lengths and higher root N contents, pointing to a fast nutrient acquisition strategy. The expression of abundant acquisitive fine roots of plants in the matorral, however, comes at the cost of larger C investment, shown by high 13C incorporation into root tissue. High root tissue densities and greater root diameter indicated that plants in the humid-temperate forest followed a resource-conservative strategy and outsource their nutrient acquisition to AM fungi. This outsourcing provides an efficient pathway to compensate a low uptake capacity of thick and dense roots. These ecosystem-specific acquisition strategies and distinct mutualism with AM fungi across the biomes will likely affect the sensitivity of plants to abiotic and biotic stressors and, thus, ecosystem responses to future climatic and environmental changes.

As wildfires have increased in extension and frequency over the past several years, research is focused on how wildfires influence ecosystem resilience, which has serious implications for the recovery and protection of native forests and plantations. Fires can drastically impact most physicochemical and biological soil properties, including soil surface mineralogical composition. However, from a bibliometric point of view, no attempt has been made to provide a comprehensive picture of the research status on fire effects in mineralogy and nutrient stocks. This work aims to evaluate fire effects on mineralogy and nutrients (FMN), the thematic evolution and determine the most relevant trends according to the intellectual structure of the knowledge built up in this research field through bibliometric analysis, using the VOSviewer software. The methodology comprises two phases: (i) Data Collection, and (ii) Bibliometric Analysis and Data Mining (Performance Analysis and Science Mapping). A detailed bibliometric analysis was performed, including 530 articles based on publications in the Web of Science (WOS) in the period 1984–2020. In general, the results demonstrate that Forest Ecology and Management is the leading journal in the field. The USA, Spain, and France are the top three countries hosting core research centers for this topic. Certini G. was the author with more citations (1395) in one paper and Johnson, D. had the more published papers (19) that received 549 citations in total. Currently, the hotspots fire issues mainly include soil nutrients (e.g. nitrogen, phosphorus, carbon, and calcium); in addition to the selected keywords, wildfires co-occurs more frequently with disturbances and terms such as soils, water quality, boreal forests, and stream. In conclusion, the growing interest in the field is evident considering 530 articles written by 1822 authors and their research exhibited in 211 journals, from universities and research centers in 60 countries.

Drylands contain most of the global soil inorganic carbon (SIC), yet its sources and vulnerability are poorly constrained. We measured SIC content and its radiocarbon (14C) at 55 dryland sites across Asia and Europe to investigate the origins of SIC and its environmental factors. In the top 10 cm, SIC generally increased with aridity, but extremely dry sites with low soil organic carbon (SOC) often had low SIC, implying that low vegetation input limits both SOC accumulation and pedogenic carbonate formation. The Δ14C of topsoil SIC was positively related to the Δ14C of SOC and declined with aridity, consistent with reduced influence of modern C sources. SIC content was linked mainly to net primary productivity (NPP) and SOC, whereas Δ14C-SIC was controlled primarily by soil pH, which governs carbonate dissolution and precipitation reactions. Thus, a greater imprint of modern carbon is found in carbonates of less alkaline surface soils, either indicating a greater potential for forming new pedogenic carbonates or greater isotopic exchange. At a subset of sites on the Chinese Loess Plateau and the Inner Mongolia Plateau, soil samples were collected across multiple depth intervals. SIC contents remained relatively constant with depth, whereas Δ14C-SIC decreased, indicating reduced contributions of recent carbon to SIC. We estimate that carbonates reflecting the influence of modern C sources accounted for about 30% of topsoil SIC but only about 10% in subsoils. These results show that dryland subsoils retain older, more stable, and likely geogenic carbonates, whereas topsoils contain younger pedogenic carbonates that are more influenced by and potentially vulnerable to environmental change.

In designed experiments, different sources of variability and an adequate scale of measurement need to be considered, but not all approaches in common usage are equally valid. In order to elucidate the importance of sources of variability and choice of scale, we conducted an experiment where the effects of biochar and slurry applications on soil properties related to soil fertility were studied for different designs: (a) for a field‐scale sampling design with either a model soil (without natural variability) as an internal control or with composited soils, (b) for a design with a focus on amendment variabilities, and (c) for three individual field‐scale designs with true field replication and a combined analysis representative of the population of loess‐derived soils. Three silty loam sites in Germany were sampled and the soil macroaggregates were crushed. For each design, six treatments (0, 0.15 and 0.30 g slurry‐N kg −1 with and without 30 g biochar kg −1 ) were applied before incubating the units under constant soil moisture conditions for 78 days. CO 2 fluxes were monitored and soils were analysed for macroaggregate yields and associated organic carbon (C). Mixed‐effects models were used to describe the effects. For all soil properties, results for the loess sites differed with respect to significant contributions of fixed effects for at least one site, suggesting the need for a general inclusion of different sites. Analysis using a multilevel model allowed generalizations for loess soils to be made and showed that site:slurry:biochar and site:slurry interactions were not negligible for macroaggregate yields. The use of a model soil as an internal control enabled observation of variabilities other than those related to soils or amendments. Experiments incorporating natural variability in soils or amendments resulted in partially different outcomes, indicating the need to include all important sources of variability. Highlights Effects of biochar and slurry applications were studied for different designs and mixed‐effects models were used to describe the effects. Including an internal control allowed observation of, e.g., methodological and analytical variabilities. The results suggested the need for a general inclusion of different sites. Analysis using a multilevel model allowed generalizations for loess soils. The results indicated the need to include all important sources of variability.

No abstract is provided for this article.

Soil compaction associated with mechanized wood harvesting can long-lastingly disturb forest soils, ecosystem function, and productivity. Sustainable forest management requires precise and deep knowledge of logging operation impacts on forest soils, which can be attained by meta-analysis studies covering representative forest datasets. We performed a meta-analysis on the impact of logging-associated compaction on forest soils microbial biomass carbon (MBC), bulk density, total porosity, and saturated hydraulic conductivity (K sat ) affected by two management factors (machine weight and passage frequency), two soil factors (texture and depth), and the time passed since the compaction event. Compaction significantly decreased soil MBC by −29.5% only in subsoils (>30 cm). Overall, compaction increased soil bulk density by 8.9% and reduced total porosity and K sat by −10.1 and −40.2%, respectively. The most striking finding of this meta-analysis is that the greatest disturbance to soil bulk density, total porosity, and K sat occurs after very frequent (>20) machine passages. This contradicts the existing claims that most damage to forest soils happens after a few machine passages. Furthermore, the analyzed physical variables did not recover to the normal level within a period of 3–6 years. Thus, altering these physical properties can disturb forest ecosystem function and productivity, because they play important roles in water and air supply as well as in biogeochemical cycling in forest ecosystems. To minimize the impact, we recommend the selection of suitable logging machines and decreasing the frequency of machine passages as well as logging out of rainy seasons especially in clayey soils. It is also very important to minimize total skid trail coverage for sustainable forest management.

Interactions between the living and non-living components of the Earth system—the biosphere and the geosphere—are the prerequisites for a habitable planet and provide the resources required by humans. Although the scale of anthropogenic global change is unprecedented, the fundamental laws of nature governing the responses of the geo- and biosphere remain unchanged. The TERRA Cluster of Excellence will investigate how geo-biosphere interactions respond to and influence environmental change. TERRA tests the hypothesis of whether the geosphere’s diversity stabilizes the biosphere and, vice versa, whether biodiversity stabilizes the geosphere – and asks: if this is the case, how? To target this challenge, one primary goal of TERRA will be to generate a discipline-overarching concept on system’s stability, applicable to the geo- and the biosphere, to quantitatively integrate the stability concept into predictive models. Based on that, the quantitative description of diversity-stability interrelationship within and across spheres is the overarching goal of TERRA.TERRA’s four research themes are organized along the continuum of different temporal and spatial scales. Theme 1 “Geo-Biosphere Interactions in the Geological Past” involves investigations at sites where high-fidelity records of past geo-biosphere interactions are well preserved across key time intervals. In one project, we will focus on the paleo-biodiversity hotspot at the Miocene site Hammerschmiede in Southern Germany. Understanding past Geo-Biosphere Interactions provides the baseline of geo-biosphere interactions without anthropogenic influence, and thus a foundation for identifying and quantifying anthropogenic impacts under contemporary and future conditions.Theme 2 “Large-Scale Contemporary Geo-Biosphere Interactions” develops a process-based understanding of present-day geo-biosphere interactions on spatial scales on which experimental manipulation is impossible. In our initial projects we aim to disentangle Geo-Biosphere Feedbacks in the FynBOS biome, a mediterranean biodiversity hotspot, and will assess how anthropogenically-enhanced species invasion can be analyzed as “local experiments” to understand self-organizational patterns in novel ecosystems.Theme 3 focuses on “Small-Scale Contemporary Geo-Biosphere Interactions” to provide mechanistic understanding of feedbacks between the geo and the biosphere on scales small enough to allow well-controlled experiments (µm to 100 m). The central field plots of our Diversitorium infrastructure form a large geodiversity manipulation experiment, modulating mineralogy, texture and climate variability independently. We will, in first projects, also investigate sites with high spatial geological heterogeneity, such as Alpine peatlands, to assess how geodiversity shapes geo-bio-systems and their stability.Across scales, Theme 4 “Geo-Biosphere Interactions in the Future” shall build and investigate future scenarios based on observational, experimental, and modeling results, guided by the principle of ’past extremes informing the future’. Using machine learning, climate and vegetation modelling, we aim to advance our understanding of past and present vegetation changes identifying the underlying complex and cascading series of biosphere-geosphere feedbacks. Model-based comparison of past and present Earth-System states allows deciphering systematic differences between dynamics under natural conditions and anthropogenic

Necromass derived from microbial turnover is a potential source of energy and nutrients to compromise the competition between microorganisms and plant in the rhizosphere. However, the role of necromass for microbial processes within the rhizosphere lacks a deep understanding of mechanisms and thus the interplay of root traits, soil temperature and necromass cannot be yet described thoroughly. Therefore, by using two root traits of maize (mutant rth3 with defective root hair prolongation and the corresponding wild type) at 20oC and 30 oC in phosphorus (P) deficient soil we tested if: i) necromass amendment provides additional labile organic matter to stimulate microbial-synthesized enzymes and hence expand rhizosphere hotspots and effeting P acquisition niches; ii) necromass addition stimulates rhizosphere microbial activities of hairless-mutant maize more than wild type regardless of temperature. Coupling in situ zymography and destructive sampling and subsequent analysis of microbial activities and plant biomass, revealed that the presence of necromass raises hotspot percentage in rhizosphere by three to fourfold at 20oC while this increment was three times lower at 30 oC. Shorter turnover time of substrate at 30 oC compared to 20oC in necromass treated soil evidently proves a faster decomposition stimulated by the concomitant warmerming and necromass-derived labile sources. Formation of fish-bone root structure beneficial from necromass addition could be a strategy of mutant maize to compensate the root hairs absence under warming resulting in outcompeting of rhizosphere microbiome for 33P uptake by plant. Decoupling alteration of Vmax and Km in necromass presence at 30oC showed that under warming stress microorganisms allocated their energy resources to synthesize more enzymes rather than increasing their efficiency. Overall, the intrinsic flexibility of plant-microbe interaction and necromass decomposition is a dynamic process that corresponds to the extent and duration of rhizosphere hotspots and mediates the adaptation of agro43 ecosystem to global warming.