Rafaela Feola Conz


Last Name

Conz

First Name

Rafaela Feola

ORCID

0000-0002-9793-5501

Organisational unit

03982 - Six, Johan / Six, Johan

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2020 - 202615
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Publications 1 - 10 of 15
  • Residues from black soldier fly (Hermetia illucens) larvae rearing influence the plant-associated soil microbiome in the short term
    Item type: Journal Article
    Fuhrmann, Adrian Julius; Wilde, Benjamin; Conz, Rafaela Feola; et al. (2022)
    Frontiers in Microbiology
    The larvae of the black soldier fly (BSFL, Hermetia illucens) efficiently close resource cycles. Next to the nutrient-rich insect biomass used as animal feed, the residues from the process are promising plant fertilizers. Besides a high nutrient content, the residues contain a diverse microbial community and application to soil can potentially promote soil fertility and agricultural production through the introduction of beneficial microbes. This research assessed the application of the residues on plant-associated bacterial and fungal communities in the rhizosphere of a grass-clover mix in a 42-day greenhouse pot study. Potted soil was amended with BSFL residues (BR+) or conventional compost (CC+) produced by Rwandan waste management companies in parallel to residues and compost sterilized (BR-, CC-) by high-energy electron beam (HEEB) as abiotic controls. The fertilizers were applied at a rate of 150 kg N ha−1. Soil bacterial and fungal communities in both fertilizer and soil were assessed by high-throughput sequencing of ribosomal markers at different times after fertilizer application. Additionally, indicators for soil fertility such as basal respiration, plant yield and soil physicochemical properties were analyzed. Results showed that the application of BSFL residues influenced the soil microbial communities, and especially fungi, stronger than CC fertilizers. These effects on the microbial community structure could partly be attributed to a potential introduction of microbes to the soil by BSFL residues (e.g., members of genus Bacillus) since untreated and sterilized BSFL residues promoted different microbial communities. With respect to the abiotic effects, we emphasize a potential driving role of particular classes of organic matter like fiber and chitin. Indeed, especially taxa associated with decomposition of organic matter (e.g., members of the fungal genus Mortierella) were promoted by the application of BSFL residues. Soil fertility with respect to plant yield (+17% increase compared to unamended control) and basal respiration (+16% increase compared to unamended control) tended to be improved with the addition of BSFL residues. Findings underline the versatile opportunities for soil fertility arising from the application of BSFL residues in plant production and point to further research on quantification of the described effects.
  • Prolonged water limitation shifts the soil microbiome from copiotrophic to oligotrophic lifestyles in Scots pine mesocosms
    Item type: Journal Article
    Jaeger, Astrid C.H.; Hartmann, Martin; Conz, Rafaela Feola; et al. (2024)
    Environmental Microbiology Reports
    Reductions in soil moisture due to prolonged episodes of drought can potentially affect whole forest ecosystems, including soil microorganisms and their functions. We investigated how the composition of soil microbial communities is affected by prolonged episodes of water limitation. In a mesocosm experiment with Scots pine saplings and natural forest soil maintained at different levels of soil water content over 2 years, we assessed shifts in prokaryotic and fungal communities and related these to changes in plant development and soil properties. Prolonged water limitation induced progressive changes in soil microbial community composition. The dissimilarity between prokaryotic communities at different levels of water limitation increased over time regardless of the recurrent seasons, while fungal communities were less affected by prolonged water limitation. Under low soil water contents, desiccation-tolerant groups outcompeted less adapted, and the lifestyle of prokaryotic taxa shifted from copiotrophic to oligotrophic. While the abundance of saprotrophic and ligninolytic groups increased alongside an accumulation of dead plant material, the abundance of symbiotic and nutrient-cycling taxa decreased, likely impairing the development of the trees. Overall, prolonged episodes of drought appeared to continuously alter the structure of microbial communities, pointing to a potential loss of critical functions provided by the soil microbiome.
  • Identifying available resources and agricultural practices useful in soil fertility management to support orange-fleshed sweet potato cultivation on smallholder farms in Mozambique
    Item type: Journal Article
    Conz, Rafaela Feola; Pujol Pereira, Engil Isadora; Abdul, Naico; et al. (2022)
    African Journal of Agricultural Research
    Orange-fleshed sweet potato is an important source of macro-and micronutrients for humans, particularly in resource-poor rural communities. However, sweet potato cultivation removes large amounts of nutrients from the soil. Hence, soil fertility replenishment is vital to secure long-term food production. The lack of access to fertilizers hinders the ability of farmers to supply and replenish soil nutrients, intensifying food insecurity. This study aimed at identifying locally available organic residues and agricultural practices with potential application in soil fertility management to prevent soil degradation in southern Mozambique. We conducted a survey to gather information on the farmers’ demographics and farming systems of 107 orange-fleshed sweet potato farmers. Results show that more than 70% of farmers use agroecological practices such as intercropping and crop rotation, and more than 90% indicated having residual crop biomass after harvest. Most cultivated crops, such as lettuce, beans, etc., are harvested in July-August, before the start of orange-fleshed sweet potato cultivation. Thus, there is potential for the application of crop residues as an organic amendment for orange-fleshed sweet potato cultivation. Nevertheless, farmers need support to adopt soil fertility management based on locally accessible resources, therefore ensuring extension services focused on the long-term benefits of sustainable practices are vital.
  • Mechanisms behind high N2O emissions from livestock enclosures in Kenya revealed by dual-isotope and functional gene analyses
    Item type: Journal Article
    Fang, Xiantao; Harris, Stephen J.; Leitner, Sonja Maria; et al. (2024)
    Soil Biology and Biochemistry
    Livestock manure contributes to global warming due to greenhouse gas (GHG) emissions, especially nitrous oxide (N2O) and methane (CH4). In the arid and semi-arid lands of Sub-Saharan Africa (SSA), extensive pastoral grazing systems are common, with cattle grazing in the savanna during the day and kept in enclosures (called bomas in Kenya) during the night. Manure is usually not removed from bomas but left to accumulate, leading to excessive local nitrogen loads, making these bomas an overlooked N2O emission hotspot in SSA that is currently not accounted for in national and regional GHG budgets. Here, we present the first in-situ isotope measurements of N2O fluxes from 37 cattle bomas along an age gradient ranging from 0 to 5 years after boma abandonment in Kenya along with functional gene analysis of soil and manure samples. The isotopic composition of the emitted N2O from bomas suggests that on average 91 ± 8% N2O was produced via bacterial denitrification and/or nitrifier denitrification, with little variation across boma age class. We also found high levels of N2O reduction to N2 across all sample sites (81 ± 9%), indicating high levels of N2O consumption. The abundances of denitrification-related genes (nirK and narG) were significantly higher than those of nitrification-related genes (amoA: AOA and AOB) in the cattle manure samples taken from the bomas, corroborating N2O emissions largely being attributed to denitrification. Significant abundance of the reduction-related gene (nosZ) also corroborated the high potential for microbial N2O reduction in bomas. Thus, by combining dual-isotope and functional gene analysis, we were able to identify source processes that govern N2O emissions from these systems. More generally, making use of the manure by spreading it in the vicinity of the bomas or on dedicated forage plots could provide a win-win by enhancing savanna productivity while simultaneously mitigating GHG emissions.
  • Soil microbial and plant responses to increasing antibiotic concentration: a case study of five antibiotics
    Item type: Working Paper
    van den Broek, Sarah W.E.B.; Nybom, Inna; Conz, Rafaela Feola; et al. (2025)
    bioRxiv
    Antibiotic contamination from biogenic waste in agricultural soils poses a significant threat to soil health and crop productivity. We investigated the effect of antibiotics on the soil microbial community, antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) and plant productivity in a six week greenhouse trial. Here, Spinacia oleracea (spinach) and Raphanus sativus (radish) were grown from seed and a mix of five antibiotics, namely sulfamethoxazole, trimethoprim, enrofloxacin, clarithromycin and chlortetracycline, were added to the soil at concentrations 0, 0.1, 1 and 10 mg kg−1 soil dry weight (c0, c0.1, c1 and c10, respectively). Overall, we found that the antibiotic treatments significantly impacted prokaryotic α-diversity and prokaryotic and fungal β-diversity. Human and plant pathogen abundance did not increase under antibiotic exposure, but there was a significant reduction of plant growth-promoting bacteria. Moreover, the c10 treatment significantly increased the abundance of MGE intI1 indicative of horizontal gene transfer and ARG sul1 antibiotic resistance and significantly lowered radish biomass and nitrogen uptake, while spinach biomass and nitrogen uptake were unaffected. In summary, our study showed that antibiotic exposure significantly changed prokaryotic community diversity and taxonomy, while fungi remained largely unaffected. The reduction of plant growth-promoting bacteria may have a significant impact on soil nutrient cycling and crop productivity, but more research is needed to understand the long-term impact of these co-applied antibiotics on food production. Additionally, more studies are needed to understand the effect of antibiotics on realistic, field scale, conditions to fully understand the impact on environmental and human health. Importance Agricultural soils are increasingly contaminated with complex mixtures of antibiotics from various biogenic sources, yet we lack a clear understanding of their specific ecological impact. While many studies investigate antibiotics, they often are studied in pollution sources like manure which contain confounding factors like heavy metals. To provide clear mechanistic insight, we investigated the effects of a complex, five-antibiotic mixture on the soil-plant system, independent of other contaminants. This revealed that the effect of antibiotics extends beyond selecting for antibiotic resistance. Specifically, the reduction of prokaryotic diversity and plant growth-promoting bacteria under antibiotic exposure can have potential detrimental effects on plant and soil health. Moreover, we found that antibiotic exposure can reduce plant biomass and nitrogen uptake, but this is highly plant dependent. This research highlights the critical need to monitor antibiotic pollution due to its potential detrimental effect on plant health and alterations to the soil microbiome.
  • Drought increases root and rhizodeposition carbon inputs into soils
    Item type: Journal Article
    Kost, Elena; Kundel, Dominika; Barthel, Matti; et al. (2026)
    Plant and Soil
    Aims Increasing droughts affect crop yield and health. Plants can respond to drought by adapting their root biomass, root morphology, and quality and quantity of rhizodeposition to improve water and nutrient uptake. Besides droughts, agricultural management influences roots and rhizodeposition; however, it is not well studied how agricultural management can affect the response of roots and rhizodeposition to drought. Methods A semi-continuous 13CO2 isotope labelling experiment was performed in a long-term field experiment comparing biodynamic, mixed conventional, and mineral conventional cropping systems. Rainout shelters were installed to induce drought. Root, net rhizodeposition, and the rhizosphere microbiome were determined at ripening of wheat. Results Drought enhanced the total root carbon mainly through the increase of fine roots. Fine root carbon under drought was primarily enhanced in the mixed conventional and biodynamic cropping system, both receiving farmyard manure, whereas no increase was measured in the mineral fertilized conventional system. Net rhizodeposition carbon was enhanced in all cropping systems under drought, particularly in the first 0.25 m. While some plant-growth-promoting genera such as Streptomyces and Rhizophagus showed relative increases under drought, other plant growth-promoting genera often involved in nitrogen fixation such as Rhodoferax and Mesorhizobium were decreased. Conclusion This field trial suggests that drought increases total belowground carbon input via fine root and net rhizodeposition carbon inputs. Since fine root carbon increased under drought in cropping systems with farmyard manure, adding manure under future drought periods could be advantageous to increase soil carbon inputs and improve nutrient foraging.
  • Locating the microbes along the maize root system under nitrogen limitation: a root phenotypic approach
    Item type: Journal Article
    Galindo-Castaneda, Tania; Kost, Elena; Giuliano, Elena; et al. (2025)
    Annals of Botany
    Background A major challenge in agriculture is the low nitrogen (N) uptake efficiency of crops, which poses environmental and economic costs. Root adaptive architectural and anatomical phenotypes in synergy with root microbes could be a promising approach to improve plant N uptake. However, little is known about such synergies. Here, we aimed to characterize the spatial distribution of the root prokaryotes of maize (Zea mays) under low N in 30-L mesocosms, where root architecture and anatomy are freely expressed, searching for correlations between prokaryotic genus abundance and ten phenotypes.Methods We studied the root prokaryotic community of 4-week-old plants growing in 30-L mesocosms under low N using two sandy soil mixtures. We collected root, rhizosphere and bulk soil samples at various locations, including depths (0-20, 20-70, 70-150 cm), root classes (lateral and axial) and root types (seminal and crown). We measured plant growth response to low N availability and performed 16S rRNA gene metabarcoding on extracted DNA.Key Results Sampling location was the third most important factor after soil mixture and compartment, explaining similar to 5 % of the variance in root prokaryotic diversity. Seminal roots (0-20 cm depth), shallow crown roots (0-20 cm) and deep crown roots (20-150 cm) showed well-separated root microbial communities. Lateral root branching density (LRBD) explained 10 % of this variance in the rhizosphere and the root tissue. We identified prokaryotic genera specific to depth, soil-root compartment, root class and type under LN. Moreover, architectural phenotypes LRBD and lateral root length significantly correlated with the abundance of 37 genera.Conclusions We highlight the importance of sampling location and architectural traits that may be associated with the microbial cycling of soil N. The exploration of synergies between root traits and microbes that participate in the N cycle has the potential to increase sustainability in agriculture.
  • Drought-induced tree mortality in Scots pine mesocosms promotes changes in soil microbial communities and trophic groups
    Item type: Journal Article
    Jaeger, Astrid C.H.; Hartmann, Martin; Conz, Rafaela Feola; et al. (2024)
    Applied Soil Ecology
    Increased tree mortality related to water limitation is documented for various species at different sites globally. Nevertheless, our understanding of tree mortality effects on soil microbial communities remains scarce. Therefore, we conducted a mesocosm experiment with young Scots pine saplings and natural forest soil with differing drought legacies to follow changes in soil microbial communities during tree mortality. Scots pine saplings were completely deprived of water during the experiment until they died. Shifts in soil microbial communities during tree mortality were assessed by metabarcoding in parallel with measurements of tree vitality and physicochemical soil properties. Drought history influenced the rate at which trees died, although high individual differences were observed. Tree death was accompanied by reduced stomatal conductance, discoloring of needles, increased defoliation, and shrinkage of the stem diameter. Soil NO3− concentrations increased after tree death, potentially through diminished plant uptake and increased microbial nitrification. Microbial abundance and community composition were affected by tree death and drought legacy. Copiotrophic bacterial taxa decreased during tree mortality, while oligotrophic taxa increased, probably slowing down soil carbon turnover. Fungal saprotrophs decreased, while symbiotrophs, such as ectomycorrhizal (ECM) fungi, increased in abundance, potentially through facultative saprothrophy and as a survival strategy of the trees in the initial phase of dying. Overall, our results indicate that drought-induced tree mortality promotes changes in soil prokaryotic and fungal communities, potentially affecting soil processes in forest ecosystems.
  • The impact of antibiotics from human excreta-based fertilizers on soil bacterial and fungal communities, antibiotic resistance genes and mobile genetic elements
    Item type: Other Conference Item
    van den Broek, Sarah W.E.B.; Nybom, Inna; Conz, Rafaela Feola; et al. (2024)
    ASM MICROBE 2024. Abstracts Online
    The use of human excreta-based fertilizers to recycle valuable nutrients is an increasingly popular approach to enhance sustainable agriculture. Despite the many potential benefits, these fertilizers may introduce antibiotics and antibiotic resistant genes (ARGs). ARGs can disseminate among soil microorganisms through horizontal gene transfer using mobile genetic elements (MGEs), which can lead to antibiotic resistant pathogens that can spread to clinical settings. To investigate the potential impact of antibiotics on the soil microbial community structure and functioning, a six-week greenhouse trial was conducted where spinach and radish were grown in soils spiked with a mixture of five widespread antibiotics (clarithromycin, sulfamethoxazole, trimethoprim, chlortetracycline and enrofloxacin), applied at concentrations 0, 0.1, 1 and 10 mg kg-1 soil dry weight. Metabarcoding of bacterial and fungal ribosomal markers coupled to qPCR-based quantification of four ARGs (sul1, dfrA12, tetQ, qnrS1) and two MGEs (intI1, intI2) was performed on collected soil samples. In our study, a canonical analysis of principal coordinates of β-diversity showed distinct bacterial groups for each antibiotic concentration, while all fungal groups overlapped except for a distinct 10 mg kg-1 treatment cluster. Antibiotic concentration and soil pH had a significant impact on both bacterial and fungal β-diversity, but α-diversity remained unchanged. Sul1 and intI1 abundance significantly increased in the 10 mg kg-1 antibiotic concentration compared to the other treatments. This can likely be attributed to persistent selection pressure in the 10 mg kg-1 treatment, where sulfamethoxazole concentration remains high enough after 6 weeks to affect the sul1 and intI1 concentrations. Overall, our findings show that these five antibiotics only induced elevated sul1 and intI1 concentrations when applied in one to two orders of magnitude higher compared to commonly detected levels in agricultural soils. IntI1, suggested as an anthropogenic pollution indicator, did not increase in the lower antibiotic concentrations which is a promising step in the research investigating the environmental and human health risks of human excreta-derived fertilizers and advancing their safe use in the future. Nevertheless, monitoring antibiotic levels in fertilizers is crucial, as even low antibiotic concentrations may increase ARGs before and after application, potentially leading to antibiotic resistant pathogens and posing clinical risks.
Publications 1 - 10 of 15