Publications

Background Main transformation pathways of low molecular weight organic substances (LMWOS) are understood, but only limited knowledge exists on their transformations in different soils and on their interactions with biochar. Aim Objectives were to study short‐term pathways of 13 C‐labelled LMWOS with different functional groups in the presence and absence of biochar in arable loess soils. Methods Soils from three sites were incubated with or without artificially aged biochar and 13 C‐labelled acetate, alanine or glucose at different rates (10 or 50 µmol C g −1 soil) at 60% water holding capacity and 15°C for 5 days, and total and substrate‐derived CO 2 ‐C and microbial biomass C (MBC) were determined and analyses of variance were calculated. Results Cumulative CO 2 ‐C (ΣCO 2 ‐C) emission was significantly ( p ≤ 0.05) affected by substrate rate and type and their interaction. Biochar significantly stimulated total, but not substrate‐derived ΣCO 2 ‐C (ΣCO 2 ‐C SD ) emission. Box‐Cox transformed MBC was significantly affected by site, substrate rate and type, whereas biochar had no significant effect. Substrate‐derived MBC (MBC SD ) and carbon use efficiency (CUE) were significantly affected by site, substrate rate and type and their interaction. Conclusions MBC SD and CUE results at low addition rate confirmed the greater importance of glucose for the build‐up of MBC compared to acetate and alanine, whereas the latter were mineralized to a greater extent. Biochar, once it is aged, which is the typical biochar form in soil, did not significantly affect build‐up of MBC SD and CUE and only slightly increased total, but not ΣCO 2 ‐C SD emission.

The central carbon (C) metabolic network harvests energy to power the cell and feed biosynthesis for growth. In pure cultures, bacteria use some but not all of the network's major pathways, such as glycolysis and pentose phosphate and Entner-Doudoroff pathways. However, how these pathways are used in microorganisms in intact soil communities is unknown. Here, we analyzed the incorporation of 13C from glucose isotopomers into phospholipid fatty acids. We showed that groups of Gram-positive and Gram-negative bacteria in an intact agricultural soil used different pathways to metabolize glucose. They also differed in C use efficiency (CUE), the efficiency with which a substrate is used for biosynthesis. Our results provide experimental evidence for diversity among microbes in the organization of their central carbon metabolic network and CUE under in situ conditions. These results have important implications for our understanding of how community composition affects soil C cycling and organic matter formation.

 The intricate interaction between human activities and the repercussions of climate change has made urban ecosystem health and biodiversity—both vital to human survival and well-being—particularly vulnerable. Recent research has spotlighted the frequently underestimated but crucial role that interactions between plant roots and several biotic and abiotic components of soil play in affecting urban biodiversity and ecosystem dynamics.We conducted a controlled experiment to investigate this relatively obscure aspect of the urban environment. The experiment has been done with young plantlets of Quercus cerris and three urban soils collected from distinct sites in the city of Campobasso (Italy). We selected three sites in the city to clearly show a specific gradient of urbanization and vegetation fragmentation. Q. cerris young plants were grown in the rhizoboxes packed with three urban soils for two weeks to evaluate the impact of soil-plant interactions on the possible enzymes’ release by the roots and root-harboring microorganisms. The spatial distribution of three enzymes, namely acid phosphatase (P-cycle), β-glucosidase (C-cycle), and leucine aminopeptidase (N-cycle), was mapped and detected in each soil region (i.e., bulk soil and rhizosphere longitudinal surface) using a 2-D soil zymography technique.The zymogram analysis revealed that the enzyme activities in soils differed spatially along the urbanization gradient, with the more urbanized soil having the highest levels of enzymatic activity and hotspot presence.The root activity toward the exudation correlated with the highest enzymatic activity, that futrther lead to more intensive turnover of soil organic matter in soil. This could be linked to the exudation of roots to regulate plant growth in unfavorable conditions or to the rhizodeposition of substrates to change soil composition. Further in-depth analyses of the physical and chemical properties of the soil, along with the profiling and characterization of the microbial community composition, are currently underway in order to obtain a better understanding of the role of root enzymatic activities and their consequences on the biogeochemical processes in urban soils.

Aims This study investigated the influence of climate and soil on the exudation rate and polysaccharide composition of aerial nodal root mucilage from drought-resistant and drought-susceptible maize varieties. Methods Two maize varieties were grown in two different soils (sandy-clay loam Acrisol and loam Luvisol) under simulated climatic conditions of their agroecological zones of origin in Kenya and Germany. The exudation rate of mucilage from the aerial nodal roots was quantified as dry weight per root tip per day and the mucilage was characterized for its polysaccharide composition. Results On average, the mucilage exudation rate was 35.8% higher under the Kenyan semi-arid tropical than under the German humid temperate climatic conditions. However, cultivation in the loam Luvisol soil from Germany led to 73.7% higher mucilage exudation rate than cultivation in the sandy-clay loam Acrisol soil from Kenya, plausibly due to its higher microbial biomass and nutrient availability. The drought-resistant Kenyan maize variety exuded 58.2% more mucilage than the drought-susceptible German variety. On average, mucilage polysaccharides were composed of 40.6% galactose, 26.2% fucose, 13.1% mannose, 11% arabinose, 3.5% glucose, 3.2% xylose, 1.3% glucuronic acid, and 1% an unknown uronic acid. Overall, significantly higher proportions of the uronic acids were found in the mucilage of the plants grown in the Kenyan sandy-clay loam soil and under the Kenyan semi-arid tropical climatic conditions. Conclusions Maize is able to enhance its mucilage exudation rate under warm climatic conditions and in soils of high microbial activity to mitigate water stress and support the rhizosphere microbiome, respectively. Graphical abstract

Microorganisms govern soil nutrient cycling. It is therefore critical to understand their responses to human-induced increases in N and P inputs. We investigated microbial community composition, biomass, functional gene abundance, and enzyme activities in response to 10-year N and P addition in a primary tropical montane forest, and we explored the drivers behind these effects. Fungi were more sensitive to nutrient addition than bacteria, and the fungal community shift was mainly driven by P availability. N addition aggravated P limitation, to which microbes responded by increasing the abundance of P cycling functional genes and phosphatase activity. In contrast, P addition alleviated P deficiency, and thus P cycling functional gene abundance and phosphatase activity decreased. The shift of microbial community composition, changes in functional genes involved in P cycling, and phosphatase activity were mainly driven by P addition, which also induced the alteration of soil stoichiometry (C/P and N/P). Eliminating P deficiency through fertilization accelerated C cycling by increasing the activity of C degradation enzymes. The abundances of C and P functional genes were positively correlated, indicating the intensive coupling of C and P cycling in P-limited forest soil. In summary, a long-term fertilization experiment demonstrated that soil microorganisms could adapt to induced environmental changes in soil nutrient stoichiometry, not only through shifts of microbial community composition and functional gene abundances, but also through the regulation of enzyme production. The response of the microbial community to N and P imbalance and effects of the microbial community on soil nutrient cycling should be incorporated into the ecosystem biogeochemical model.

Paddy soils regularly experience redox oscillations during the wetting and draining stages, yet the effects of short-term presence of oxygen (O2) on in-situ microbial hotspots and enzyme activities in anoxic ecosystems remain unclear. To fill this knowledge gap, we applied soil zymography to localize hotspots and activities of phosphomonoesterase (PME), β-glucosidase (BG), and leucine aminopeptidase (LAP) in three compartments of rice-planted rhizoboxes (top bulk, rooted, and bottom bulk paddy soil) under oxic (+O2) and anoxic (O2) conditions. Short-term (35 min) aeration decreased PME activity by 13–49 %, BG by 4–52 %, and LAP by 12–61 % as compared with O2 in three soil compartments. The percentage of hotspot area was higher by 3–110 % for PME, by 10–60 % for BG, and by 12–158 % for LAP under +O2 vs. O2 conditions depending on a rice growth stage. Irrespective of the aeration conditions, the rhizosphere extent of rice plants for three enzymes was generally greater under higher moisture conditions and at earlier growth stage. Higher O2 sensitivity for the tested enzymes at bottom bulk soil versus other compartments suggested that short-term aeration during conventional zymography may lead to underestimation of nutrient mobilization in subsoil compared to top bulk soil. The intolerance of anaerobic microorganisms against the toxicity of O2 in the cells and the shift of microbial metabolic pathways may explain such a short-term suppression by O2. Our findings, therefore, show that anoxic conditions and soil moisture should be kept during zymography and probably other in-situ soil imaging methods when studying anoxic systems.

Interest in managing agroecosystems for improving soil health has driven the application of conservation practices, such as reduced tillage. However, our understanding remains limited regarding changes in soil organic carbon (SOC), microbial resource limitations, and soil ecosystem multifunctionality across the soil profile (not just in the upper layers) following long-term reduced tillage as compared to conventional tillage. This study aimed to compare the impacts of reduced tillage (RT) and conventional tillage (CT) on SOC storage, soil enzyme activities, and ecosystem functionality in a 90 cm soil profile. Soil cores were collected from four different soil depths (0–10, 10–30, 30–50, 50–90 cm) in a 55-year field experiment (crop rotation primarily featured cereals) in central Germany comparing RT (rotary harrow, 5–8 cm depth) and CT (mouldboard plough, 25 cm depth). Results showed that RT increases SOC content by 24 % at 0–10 cm depth but decreases SOC content by 22 % at 10–30 cm depth relative to CT. The enhanced SOC content under RT further improved soil ecosystem multifunctionality by a factor of 2.8 at 0–10 cm compared to CT. Notably, higher available nitrogen (N) content increased vector length at 0–10 cm depth under RT, related to the higher production and release of C-acquisition enzymes. In contrast, the higher exudation of N-acquiring enzymes found at 10–50 cm depth indicated N limitation for microorganisms under RT. At this depth, CT alleviated microbial N limitation. Moreover, RT lowered SOC stock by 24 % compared to CT at 10–30 cm, resulting in an 11 % decrease in SOC across the entire 0–90 cm soil profile. In conclusion, while reduced tillage improved soil ecosystem functionality in the 0–10 cm, it may not enhance SOC sequestration, highlighting the importance of considering the whole soil profile when comparing the SOC sequestration potential of different tillage practices.

Neben Stickstoff ist Phosphor (P) das wichtigste wachstumslimitierende Nahrelement in Boden. Dennoch gibt es wenig Information uber die raumliche Heterogenitat des P-Gehaltes in Waldboden. Daruber hinaus ist der Effekt einer homogenen versus heterogenen P‑Verteilung im Boden auf die mikrobielle P‑Akquirierung und Zusammensetzung der mikrobiellen Gemeinschaft weitgehend unbekannt. Ein Rhizotronexperiment mit P-armem Waldboden wurde durchgefuhrt um konkurrierende P‑Aufnahmestrategien von Mikroorganismen zu untersuchen. Um den Effekt raumlicher P‑Heterogenitat auf pflanzliche und mikrobielle P‑Aufnahme zu eruieren wurden mit F.sylvatica bepflanzte Rhizotrone mit P‑33‑Eisen(III)phosphat, einer relativ immobilen P Quelle, in verschiedenen raumlichen Verteilungen markiert. Die P‑Mobilisierung durch Mikroorganismen wurde mittels einer verbesserten P-33-PLFA-Methode verfolgt, welche die P‑33‑Inkorporierung in Mikroorganismen mit Anderungen in der Zusammensetzung mikrobieller Gemeinschaften in situ verbindet. Die mikrobielle P-Aufnahme war erhoht in Rhizotronen mit hoher P‑Verfugbarkeit, sowie in solchen mit heterogener P‑Verteilung. Charakteristische PLFA weisen auf eine Akkumulation von Ektomykorrhizapilzen, typischerweise assoziiert mit Buchenwurzeln, in P‑reichen Arealen hin. Diese Ektomykorrhizzapilze fuhren wahrscheinlich zu einer starken Zunahme der P‑Mobilisierung des ausgebrachten P‑33‑Eisen(III)phosphats in stark P-haltigen Habitaten. Im Gegensatz hierzu benotigen Habitate mit niedriger P-Verfugbarkeit eine komplexer zusammengesetzte mikrobielle Gemeinschaft um unzugangliche P-Quellen zu mobilisieren. Entsprechend fordern hohe P‑Vorkommen die Bildung von Pilzhyphen zur P-Mobilisierung – ein Effekt, der mit sinkendem P-Gehalt abnimmt. Des Weiteren zeigen grampositive und ‑negative Bakterien eine massiv erhohte P‑Aufnahme unter zunehmend heterogenen P-Verteilungen. Sie stellen jedoch einen kleineren Anteil der mikrobiellen Gemeinschaft als in homogen P‑angereicherten Rhizotronen, was auf einen Vorteil filamentoser Organismen bei heterogener P-Verteilung hindeutet. Entsprechend fordert eine heterogene P-Verteilung in Waldboden die P-Aufnahme mikrobieller Gemeinschaften aus mineralischen P-Quellen mit geringer biologischer Verfugbarkeit in Waldboden.

Abstract Background and Aims Multiple biotic and abiotic stressors increasingly threaten tropical grasslands, yet restoration efforts predominantly prioritise aboveground traits, neglecting critical belowground traits essential for ecosystem resilience and recovery. We proposed that these neglected traits shape ecosystem biodiversity, productivity, and stress tolerance. This study assessed biomass yield, root and rhizosphere traits, resource acquisition strategies, and soil microbial communities in selected perennial grasses used for forage and seed-based restoration. We also evaluated enzymatic activity and microbial functional potential related to carbon, nitrogen, and phosphorus cycling. Methods In a long-term restoration project in a tropical semi-arid grassland, we measured plant biomass, root morphology, mycorrhization, extracellular enzyme activities, and rhizosphere microbial community composition and function. Results Eragrostis superba had the highest shoot biomass, while Cenchrus ciliaris showed the highest root biomass and mycorrhization. The root trait–microbiome associations revealed distinct resource acquisition strategies: Chloris roxburghiana and Enteropogon macrostachyus displayed a ‘do-it-yourself’ strategy supported by copiotrophic rhizomicrobiome, while C. ciliaris displayed an ‘outsourcing’ strategy. Conversely, E. superba displayed high intraspecific root trait variation, exhibiting partially ‘do-it-yourself’ and ‘outsourcing’ traits. Grass species significantly influenced fungal, but not bacterial, community composition and favoured nutrient recycling over direct nutrient acquisition, with recycling strategies varying among species. Conclusion Root traits and belowground plant–microbe interactions shape ecosystem function in tropical grassland restoration. Selected species occupied distinct successional niches, from early colonisation ( C. ciliaris ) to late-stage productivity ( E. superba ). Integrating these traits into restoration frameworks is essential for enhancing ecosystem resilience, productivity, and successful long-term ecological restoration outcomes.