Soil microbial basal respiration is a proposed biological indicator of soil health and a key parameter in studying microbial carbon cycling. It is commonly quantified in closed-chamber incubations by measuring the increase in CO₂ concentration in the vial headspace over time compared to a known background. Assuming a linear CO₂ increase solely caused by microbial activity, respiration rate estimates derived between 1 and 24 hours should compare, but differences have been observed previously.

To investigate how and why estimates of microbial respiration rate vary with incubation duration and amount of soil, gas samples were collected at 12 time points over a 24-hour period for ten soils covering two texture categories and a gradient of organic carbon content.

Microbial respiration rate was on average 3.4-fold higher after 1 hour than after 24 hours. The apparent decline in microbial respiration over time was related to a violation of the assumption that the sample CO₂ concentration at the beginning of the incubation equals the assumed background in soil-free blanks. Follow-up experiments indicated that the dissolution of CO₂ in the soil solution during the pre-incubation can cause an initial peak in emissions at the start of the incubation (i.e. CO₂ artefact) through shifts in chemical equilibria caused by the method itself, which can be misinterpreted as high initial respiration rates.

Over time, the contribution of the method’s artefact decreases. Factors like soil moisture, amount of soil incubated, microbial activity rate, and chamber closure timing affect the artefact's magnitude. Optimising incubation duration and headspace-to-soil ratio (e.g. 24-hour incubation at 22 mL vial : 1 g soil) can mitigate the effect of the CO₂ artefact and produce unbiased estimates of microbial respiration rates.

How to cite: Schroeder, J.: CO2 artefact can distort estimate of microbial basal respiration rate in closed chambers , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8038, https://doi.org/10.5194/egusphere-egu25-8038, 2025.

Introduction

Soil respiration is an important part of the carbon cycle and is a significant terrestrial carbon source. There is currently very limited research focused on characterising soil respiration in Singapore, and even among studies conducted in Southeast Asia, most of the research focuses on primary forests rather than urbanized soils. The objectives of this study were to assess the variation of soil respiration with land use, characterise the daily cycles of soil respiration and identify the factors which drive soil respiration in an urban catchment.

Methods

Soil Respiration was measured at 7 forests sites and 12 urban park sites in Singapore, using a portable Li Cor Soil Respiration Smart Chamber.  Soil samples were also collected from each of the sites and their nutrient concentrations were quantified. Additionally, at one park and one forest, the daily cycle of soil respiration was measured from 7 am to 7pm, where half hourly measurements were taken, along with corresponding measurements of soil temperature and moisture. 

Results & Discussion

When comparing soil respiration rates between parks and forests, we found that, on average, respiration rates in the forests were slightly higher than those in the parks (Forests – 3.62, Parks – 3.46 umol CO2.m^-2s^-1) (Fig 1), but the difference was not statistically significant (Wilcox test p value > 0.05).

Next, the daily variation of soil respiration was characterised and our results revealed that the magnitude of variation in soil respiration throughout the day was small (Forest: 2.34-2.52, Park: 3.80-4.26 umol CO2/m².s) (Fig 2). This lack of variation can be explained by relatively minor changes in soil temperature and moisture. Soil temperatures in Singapore did not vary much throughout the day (Forest: 26.2 – 28.0⁰C, Park: 27.1 – 30.3⁰C), and as previous research shows, more significant changes in temperature are required to see significant changes in soil respiration.

Finally, in order to determine what factors affected soil respiration, the relationship between soil nutrients and soil respiration was assessed. Results revealed that only NO3^- was strongly positively correlated with soil respiration and a linear regression analysis revealed that soil nitrate concentrations explained about 50% of the variation of soil respiration (Adjusted R² = 0.503, p<0.05). Other nutrients like phosphate, ammonium and dissolved organic carbon has no significant relationship with soil respiration.

Fig 1: Variation of Soil Respiration by Land use

Fig 2: Daily cycle of Soil respiration in a park and forest

In terms of future work, we also plan on conducting soil respiration measurements on managed land use types like agriculture and golf courses. Additionally, we plan on further characterising temporal variations of soil respiration, including diurnal and seasonal variations, across land use types. Finally, we will collect additional data on soil parameters like total organic carbon, microbial populations and community diversity and use these to develop models for soil respiration as well.

Acknowledgements

This research grant is funded by the Singapore National Research Foundation under its Competitive Funding for Water Research (CWR) initiative and administered by PUB, Singapore’s National Water Agency.

How to cite: Senaratna, K. Y. K., Te, S. H., Fatichi, S., and Gin, K. Y.-H.: Characterising Soil Respiration rates across different land uses in a Tropical Urban Catchment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13880, https://doi.org/10.5194/egusphere-egu25-13880, 2025.

Recent climatic changes have increased the unpredictability of rainfall events with a heightened probability of droughts, thus influencing the belowground carbon sequestration. Soil structure is shaped by physical, chemical, and biological processes and their interactions. Droughts are linked to the loss of soil structural stability, reduced pore-water connectivity, and organic carbon transport, therefore affecting soil microbial activity. The protection of carbon within the soil matrix is majorly driven by its accessibility to microbial decomposers and is also determined by the abundance of soil pores of a specific size range. In this study, we investigated the effects of drought on soil pore characteristics like pore size distribution, porosity, distances to pores, and biochemical properties such as microbial biomass carbon, ergosterol content, and soil organic carbon. The study site was a Long-term Ecological Research experiment of a short grass steppe ecosystem with treatments of 66% rain exclusion (regarded as drought) and control plots in a randomized complete block design. Dominant plant species include C4 grasses, blue grama (Bouteloua gracilis), buffalo grass (Buchloe dactyloides), and C3 plains prickly pear cactus (Opuntia polyacantha). This study aims to understand the importance of soil structure in interaction with organic matter and microbial activity. Intact soil cores of 5 cm in height by 5 cm in diameter were collected from 5-10 cm of soil depth to derive the soil pore characteristics using the X-ray computed microtomography technique (X-ray µCT, resolution of 18 µm). Bulk and intact soil samples were collected during the fifth year of the treatments in place.

The results demonstrated that drought differentially affected pores of different size ranges, substantially increasing volumes of > 60 µm diameter pores, and decreasing the volumes of 36-60 µm pores, while not affecting <18 µm pores. Drought decreased total volume, number of fragments, and fragment size of soil POM, and markedly decreased microbial biomass,  and enzyme activities. Furthermore, the bulk soil samples were analyzed for base chemical properties such as pH, cation exchange capacity, available phosphorus, exchangeable potassium, magnesium, and calcium We surmise that a 5-year drought in SGS prairie soils,  despite increasing the volume of medium-sized pores and pore connectivity, the lower microbial quotient (qMic), along with higher metabolic quotient (qCO₂) contributes to greater loss of C as CO₂ and slower C accumulation in the soil.

How to cite: Thotakuri, G., Dor, M., Guber, A., Kravchenko, A., and Smith, M.: Long-term drought alters pore structure and biochemical characteristics in soils of short-grass steppe, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4470, https://doi.org/10.5194/egusphere-egu25-4470, 2025.

Agricultural soils contribute as major polluters of nitrous oxide (N₂O) emissions in Europe, which are a result of microbial nitrification and denitrification processes. Nitrification inhibitors (NI) have gained attention by decreasing N₂O emissions and nitrate leaching, thereby promoting the uptake of nitrogen (N) by plants. However, concerns have been raised about the long-term efficiency of NI at the scale of microbial communities, for example if taxa develop resistance. This work hypothesises that target and non-target microbial taxa develop resistance to NIs over time after showing initial sensitivity to 3,4-Dimethylpyrazole phosphate (DMPP) application. More in depth, specific nitrifying organisms will be less resilient against DMPP in an agricultural field with a high clay/sand ratio. Lastly, different types of fertilizations interact differently with DMPP, creating a change in the response of Ammonia oxidizing bacteria and archaea gene abundance.

The study was conducted on agricultural fields located in Köningslutter, Lower Saxony (Silt loam) and Hohenhiem, Baden-Wuerttemberg (Silty clay loam). One of three distinct fertilizers was applied to each field, specifically ammonium sulphate nitrate, slurry or urea ammonium nitrate solution, in combination with or without DMPP. Samples were taken at four different time points over the growing season of winter wheat. Additional physicochemical parameters including N mineralisation rates, pH, carbon and N content, and respiration rates of CO₂, N₂O and CH₄ were measured simultaneously. Microbial communities were analysed with qPCR targeting functional genes related to nitrification and denitrification (amoA and nosZ1/2, respectively). Amplicon sequencing of universal prokaryote taxonomic markers and amoA was performed to investigate the response of target and non-target taxa to DMPP addition over time. Statistical analyses are being conducted.

How to cite: Groven, A.-C., Wonneberger, A., Binder, I., Russer, R., Pacholski, A., Finn, D., and Tebbe, C.: The impact of the nitrification inhibitor DMPP on agricultural soil microbial communities, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19893, https://doi.org/10.5194/egusphere-egu25-19893, 2025.

Conventional petroleum-based plastics are non-degradable materials that are difficult to degrade during disposal and landfill after use; therefore, they have an adverse environmental impact over a long period of time. An example is the problem of soil landfill of agricultural mulching films, which are discarded after agricultural activities. Plastic particles alter the physicochemical properties of the soil, resulting in reduced crop yields and disruption of nutrient cycling within the soil ecosystem, while also impacting groundwater contamination. Furthermore, they serve as carriers for organic pollutants such as heavy metals, pesticides, and herbicides, causing greater environmental contamination. To solve this problem, there has been a growing interest in bioplastics as alternatives to conventional fossil-based plastics, particularly in the agricultural field. In order to reduce the pollution load in the soil through the utilization of bioplastics, it is essential to thoroughly understand the microorganisms involved in biodegradation and their corresponding biodegradation characteristics within soil and compost environments. Therefore, in this study, microbial communities were characterized during the degradation of two bioplastics (Polylactic acid (PLA) and Polybutylene adipate terephthalate (PBAT)), under mesophilic (35℃) and thermophilic (58℃) composting conditions. PLA and PBAT films and granules were buried in chicken manure compost, and the biodegradability was assessed based on the weight loss over time. PLA film was degraded rapidly, by 41.5% in 5 days and by 91.15% in 10 days under thermophilic composting conditions, and completely degraded in 15 days. Under mesophilic composting conditions, PLA film showed a degradation rate of 17.9% in 20 days. To characterize microbial communities during the bioplastics degradation, compost samples near the bioplastics were collected, followed by DNA extraction. The 16S rRNA gene region was amplified using the 515F/806R primer set to investigate the bacterial community, as well as the ITS2 gene region using the ITS3/ITS4 primer set to analyze the fungal community. Subsequently, the sequences were analyzed using Illumina Miseq. The information obtained in this study can be used to secure promising bioresources to enhance bioplastics degradation.

How to cite: Cho, K.-S., Cho, I., and Kim, G.: Characterization of Microbial Communities during Bioplastics Degradation in Mesophilic and Thermophilic Composting Conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3918, https://doi.org/10.5194/egusphere-egu25-3918, 2025.

The use of biochemicals in agriculture has become crucial to meeting the global demand for food production. Agrochemicals, such as fertilizers and pesticides, are widely applied to enhance crop efficiency. Additionally, other chemicals like nitrification inhibitors offer the potential to mitigate the environmental impact caused by the excessive use of fertilizers. While their effects on targeted microbial taxa are known, their broader environmental risk to the entire microbial community remains poorly understood.

Considering the urgency of assessing these risks, extraction and deep sequencing of total RNA offers a powerful approach to unveil non-target effects without favoring specific taxa or introducing bias from dead or dormant biomass. By simultanously analysing rRNA and mRNA, it is possible to investigate negative effects not only on the activity of specific taxa but also on critical ecosystem functions providing the potential to discover previously unknown effects.

Here, we demonstrate how total RNA analysis can enhance our understanding of non-target effects of agrochemicals on microbial soil communities. In the GENEPEASE II project, the impact of the commercial fungicide Prosaro was examined using soil microcosms over a 6 months period. Besides the expected decline in fungal taxa, significant effects on the overall microbial community were observed, as indicated by shifts in the rRNA and the gene expression profiles (all ANOVAs p < 0.05). Ongoing in-depth analyses will identify individual taxa affected by the fungicide. By linking these taxa to their ecological roles in natural settings and identifying up- and downregulated genes, we aim to pinpoint ecosystem functions that are potentially affected by the use of the fungicide.

Moving forward, this method will be applied to a field trial investigating the non-target effects of nitrification inhibitors nitrapyrin and DMPP. Both compounds have the potential to reduce emissions of the greenhouse gas N₂O. In this context, the analysis of mRNA provides an opportunity to investigate potential impacts on enzymes closely related to ammonia monooxygenase, the primary target of nitrification inhibition. Such effects could potentially impact greenhouse gas-regulating processes, such as methane oxidation, and therefore counteract the positive environmental benefits of nitrification inhibition.

Ultimately, refining this method for the presented experiments will help to develop a robust approach for utilizing total RNA in various agrochemical applications. Thus, total RNA analysis can serve as a crucial tool for incorporating microbial community data into environmental risk assessments, therefore contributing to a more sustainable future in agriculture.

How to cite: Horstmann, L., Gözdereliler, E., Zervas, T., Donhauser, J., Nielsen, C. S., Kjøller, R., Ekelund, F., Priemé, A., Jacobsen, C. S., and Ellegaard-Jensen, L.: Environmental risk assessment at the microbial level: utilizing total RNA sequencing to evaluate the non-target impact of biochemicals in agriculture, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21642, https://doi.org/10.5194/egusphere-egu25-21642, 2025.

Soil organic carbon (SOC) is a key indicator of healthy soils. Among the sources contributing to the SOC pool, the role of microbial biomass and especially necromass is often overlooked. Microbial necromass sometimes reaches 40 times of the microbial biomass, emphasizing the role of soil microorganisms in carbon sequestration. However, overall, determining necromass in soils is not common. In this study, we aimed to examine (i) the microbial biomass and necromass in agriculturally used soils across Austria, Central Europe, and (ii) the effect of environmental factors and soil parameters on biomass-necromass contributions in arable and grassland ecosystems.

We sampled soils (soil corer with 2.5 cm diameter and 10 cm depth, 3 samples per site) from 400 sites across Austria, from 150 m a.s.l. up to 2500 m a.s.l. including croplands, grasslands, and grass strips. The cooled samples were analysed for microbial biomass using Chloroform Fumigation Extraction (CFE) and for microbial necromass using amino sugars extraction. Moreover, composite soil samples (2.5 cm diameter, 10 cm depth; 3 samples per site) were used to determine pH (CaCl₂), SOC, texture, potassium, phosphorus, nitrogen, humus content. The climate data (mean annual air temperature and annual precipitation) was obtained from Geosphere Austria, the Austrian Federal Agency for Geology, Geophysics, Climatology and Meteorology, Vienna. Soil management data was obtained through questionnaires directly from the land owners or operators. Data were statistically analysed using CatBoost models.

Average microbial carbon (MC) across sites was 401 ± 256 mg g^-1 and microbial nitrogen (MN) 65.0 ± 48.9 mg g^-1. Both MC and MN significantly increased in the order croplands < grass strips < grasslands (HSD, p<0.001). Preliminary analyses showed specific effects of soil and environmental parameters on the proportion of microbial biomass and necromass in the soils.

Our results indicate that land use significantly impacts microbial biomass distribution, potentially affecting nutrient cycling and soil health. Understanding these dynamics could inform land management practices aimed at improving soil fertility and mitigating climate change through enhanced carbon sequestration.

How to cite: Monoshyn, D., Mittmannsgruber, M., Wiedenegger, E., Gruber, E., Murugan, R., Inselsbacher, E., and Zaller, J. G.: Microbial Biomass and Necromass in Austrian Soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3553, https://doi.org/10.5194/egusphere-egu25-3553, 2025.

Ukraine is prosperous in agricultural activities. Agricultural land covers 68.5% of the total land area. Additionally, Ukraine exports around 10% of the global cereals abroad and thus plays an important role in global food security. Crop production in Ukraine is dominated by grains (wheat, barley, corn), technical crops (sunflowers, sugar beets), potatoes¹. Livestock production is dominated by poultry, pigs, cows¹.  However, agricultural activities have been under threat over the past two decades. An important reason is climate change. Climate drivers such as temperature and precipitation have changed their patterns in space and time in Ukraine since 2000. The implications of those changes on agriculture are poorly studied, namely on crop yield, synthetic fertilizers, and animal manure. Furthermore, the potential implications of agriculture and climate on future water scarcity are unknown considering the ongoing Russian-Ukrainian war.

In this study, we aim to assess the relationship between climate drivers and agriculture in Ukraine over the past two decades (2000-2020) and discuss the potential implications of these drivers on future water scarcity considering the Russian-Ukrainian war as an additional (unexpected) threat. We do this in a spatially explicit way. We collect the following data for agriculture: crop yield, crop area, fertilizers, irrigation². Data for climate drivers include air temperature and precipitation³. For agriculture, data is based on one-year time steps, and data for climate drivers is seasonal every year between 2000 and 2020. We map the data for 24 provinces in Ukraine. We also show the historical changes over the studied period. From a historical perspective, we identify the main relationship between the climate drivers and agricultural aspects by province in Ukraine. We take these insights and discuss how water scarcity would change in the future if climate change and food production continue following the historical pattern, and consider the war as an additional threat. One of the results shows that water quantity is influenced by climate change; examples are droughts (less precipitation over time). Water quality is influenced by agricultural runoff and war activities; examples are too many nutrients from agriculture in rivers and too many emerging pollutants from destroyed treatment facilities.

Keywords: agriculture, climate parameters, water scarcity, drivers, implications

Acknowledgments: European Union HORIZON-MISS-2023-OCEAN-SOIL-01 Grant Agreement No. 101156867 (Path4Med).

1: European Parliamentary Research Service: Ukrainian agriculture, PE 760.432 – April 2024

2: The online platform AgroStats: Agricultural statistical data in Ukraine (1980-2023)

3: Climate Change Viewer platform: air temperature and precipitation in Ukraine (1981-2020)

How to cite: Strokal, V., Labenko, O., Ladyka, M., Palamarchuk, S., Naumovska, O., Vagaliuk, L., and Voitenko, L.: Relationship between climate drivers and agriculture in Ukraine: changes over the past two decades and potential implications on water scarcity in the future, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6172, https://doi.org/10.5194/egusphere-egu25-6172, 2025.

Tropical peat swamp forests are critical components of the global carbon (C) and nitrogen (N) cycles, with microbial decomposers playing a pivotal role in the assimilation of these elements through the activity of extracellular enzymes in the soil. This study examines the impact of C and N decomposition on microbial enzymatic activity in the Padang Alan soil of the Maludam peat swamp forest, Sarawak. To evaluate the role of extracellular enzymes in driving C and N cycling, soil samples were collected at four depths (0–10 cm, 10–50 cm, 50–100 cm, and 100–150 cm) and subjected for enzymatic assays. C-acquiring enzymatic activities were assessed using β-1,4-glucosidase and phenol oxidase, while N-assimilation activity was measured using β-1,4-N-acetylglucosaminidase. The findings revealed that both C- and N-acquiring enzyme activities peaked at the 0–10 cm depth, where organic matter decomposition is most active, and declined with increasing depth. This pattern underscores the dominance of enzymatic activities in the top soil layers, where decomposition processes are most dynamic. Additionally, N decomposition is influenced by the progression of lignin degradation during decomposition process. Although enzymatic responses varied with soil depth, edaphic factors were found to control enzymatic activity predominantly. These results deepen our understanding of microbial-mediated nutrient cycling in tropical peat soils and emphasize the relationship between soil depth, enzyme activity, and nutrient cycling. Nonetheless, enzymatic activity can be varied by forest type, and elucidating the microbial nutrient demand in peat soil provides important insights into nutrient cycling of tropical peatland ecosystems.

How to cite: Lindang, H. U., Lau, S. Y. L., Laing, R. S., Raczka, N. C., and Melling, L.: Soil Enzyme Activity in Tropical Peat Swamp Forest : Insights from Sarawak, Malaysia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15871, https://doi.org/10.5194/egusphere-egu25-15871, 2025.

Arid regions are increasingly impacted by water scarcity and land degradation driven by both anthropogenic pressures and natural factors. In Jordan, a predominantly arid country, strategies have been implemented to mitigate these challenges and adapt to the changing climate. Among these strategies, Marab Water Harvesting Technology (WHT) has been established as a key method for sustainable water management. Traditionally, the cropping system in Marab areas has focused on barley monoculture, which limits the production of ecosystem services. To enhance the production of these positive externalities, vetch (Vicia sativa), a leguminous crop, has been introduced into the cropping system. This diversification aims to improve soil fertility and the quality of fodder available for livestock, and to support sustainable agriculture. Preliminary field data are promising, confirming the effectiveness of Marab WHT in providing sufficient water for vetch cultivation, consistent with existing literature. Additionally, vetch has improved total soil nitrogen and organic matter in the Marab cropping system. To further evaluate the scalability and resilience of this cropping system under varying climatic conditions, the FAO AquaCrop model is being employed to test its application in different regions and its adaptability to climate change.

How to cite: Strohmeier, S., Renzi, N., Castelli, G., Bresci, E., Al Widyan, J., Hilali, M. E.-D., and Haddad, M.: Enhancing Ecosystem Services of Marab Water Harvesting Technology: Integrating Vetch into Traditional Barley-based Cropping Systems for Soil Fertility Restoration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16522, https://doi.org/10.5194/egusphere-egu25-16522, 2025.

The Geological Survey of India (GSI) conducted an extensive geochemical survey under the National Geochemical Mapping (NGCM) project in Odisha, analysing 28,115 stream sediment samples. This study focused on 10 potentially toxic elements (Co, Cu, Cd, Cr, Zn, W, As, Mn, Ni, and V) from a dataset of 51 elements to evaluate soil contamination across the state. Multivariate statistical techniques revealed significant inter-element relationships, while Geographic Information System (GIS) methods were employed to generate interpolated geochemical distribution maps. The study identified a concentration hierarchy of Cr > Mn > V > Zn > Ni > Cu > Co > Cd > As > W among the elements, with Spearman correlation analysis indicating strong associations among Cd and W. Soil contamination levels were evaluated using pollution indices such as the geo-accumulation index (Igeo), contamination factor (CF), Pollution Load Index (PLI), and Potential Ecological Risk Index (PERI). The results revealed moderate to high pollution levels in Odisha's northern and southwestern regions, primarily driven by Cd, W, Cr, and Ni. Principal Component Analysis (PCA) identifies four significant components in the dataset, with distinct contributions from various elements. PC1, accounting for the largest variance, is primarily influenced by Cd (17%), Cr (16%), and Ni (14%), suggesting a strong association with ultramafic geological sources, sulfide mineralization, or to some extent industrial pollution. In contrast, PC2 is dominated by Co (26%), Mn (23%), Cu (21%), and Zn (18%), which are often linked to metalliferous inputs, soil geochemistry, and anthropogenic activities such as mining and industrial discharge. Health risk assessment showed children were more vulnerable to Co, Cr, V, As and Cd toxicity in the study region. Whereas, Cd, Cr, and Co are major risk contributors for adult males and females. The hazards associated with non-carcinogenic and carcinogenic soil metals exceeded tolerable thresholds. The computed Hazard Index indicates that soil particle ingestion is the primary exposure pathway associated with elevated risk, succeeded by dermal contact. The results endorse the formulation of targeted remediation plans and policies to mitigate health concerns linked to these polluted soils.

How to cite: Dey, P., Tripathy, S., and Pruseth, K. L.: Evaluation of Potentially Toxic Element Contamination and Related Health Risk Assessment in Soil of Odisha, India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18753, https://doi.org/10.5194/egusphere-egu25-18753, 2025.