Plant derived organic matter (OM), entering soils either as aboveground plant litter or via belowground rhizodeposition or dead roots, undergoes microbial mineralization and transformation and finally ends up in various soil OM (SOM) pools. With two major solid SOM pools besides dissolved OM, namely particulate OM (POM) and mineral-associated OM (MAOM), the initially plant dominated OM is progressively transformed into microbial OM during decomposition. However, as mineral soils comprise highly heterogeneous systems over a wide range of spatial and temporal scales, the microbial transformation of plant OM and the formation of SOM is highly variable in time and space as well. Processes controlling the persistence of SOM are especially determined at nm to µm scales at biological highly active biogeochemical interfaces. Thus, plant litter and roots form distinct soil hot spots for interactions between microbiota, OM and mineral particles that are thought to control the long-term fate of soil carbon. The detritusphere and rhizosphere thus represent soil volumes that host the complex interplay of biological, chemical and physical soil processes that determine the fate of SOM. We will highlight the intricate connection between the transformation of plant derived OM via microbial processing and soil structure formation that lead to the build-up of persistent SOM.   

How to cite: Mueller, C. W.: Plants, microorganisms and soil minerals, how the persistence of soil organic carbon is regulated at microscale interfaces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21758, https://doi.org/10.5194/egusphere-egu24-21758, 2024.

Soil zymography represents a non-invasive methodology facilitating the in situ visualization and localization of potential enzyme activities in soil. Due to universality and simplicity of zymography method, it has been widely used to visualize the hidden microbial and root life in soil, which is a very heterogeneous and “dark” environment.

Following the pioneering use of fluorogenic substrates for enzyme activity visualization in soil, a significant methodological advancement occurred within the subsequent decade. Our primary focus is to highlight the progress in the last 10 years, with respect to the spectrum of enzyme activity imaging, zymography resolution, standardization and hotspot identification. Specifically, we emphasize the integration of zymography with the visualization of soil acidification, root exudation, pore distribution, nutrient and water movements. Although the majority of applications so far have centered on enzyme activities in the rhizosphere to reveal plant-soil-microbial interactions, we present the case studies to identify soil heterogeneity and microbial activity also in biopores, detritusphere and other hotspots.

We present not only the advancements made but also the current possibilities, challenges, and the potential directions of soil zymography. This technique finds applications across natural and agricultural ecosystems, both in field settings and laboratory studies, capable of scaling from the entire root system (dm) down to microbial communities (μm).

In the decade ahead, the future of enzyme research, particularly zymography imaging, will continue to broaden the scope of microbial studies and hotspot localization. This expansion will involve integrating with disciplines such as (bio)chemical, physico-chemical, microbial cell imaging, and isotope applications, facilitating a deeper understanding of soil processes and microbial interactions.

How to cite: Bilyera, N. and Kuzyakov, Y.: Soil zymography: a decade in microbial hotspot imaging and future challenges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2546, https://doi.org/10.5194/egusphere-egu24-2546, 2024.

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.

How to cite: Gillini, A., Bilyera, N., Trupiano, D., Loginova, I., Dippold, M., and Scippa, G. S.: Rooted in the city: Unveiling the hidden world of Quercus cerris enzymatic activity in urban soils , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-976, https://doi.org/10.5194/egusphere-egu24-976, 2024.

In recent decades, the potential use of chars, such as biochar or hydrochar, as soil amendments to enhance plant growth, has garnered significant interest. However, understanding potential toxic impact of these materials on soil and plants remains an area requiring further exploration. In this study, the effect of applying hydrochar (HC) derived from chicken manure on the yield and nutritional quality of sunflower (Helianthus annuus L.) seeds was assessed under both well-irrigated and water deficit (WD) conditions. To address it, the HC was applied to a Cambisol at rates of 3.25 and 6.5 t ha^-1. Mineral fertilizer treatments with equivalent total nitrogen contributions as the amendment were included for comparison. Sunflower plants were cultivated in pots under two irrigations conditions (60 and 30% of the soil water holding capacity). After 77 days of cultivation, the plants were harvested, and the content of macro- and micronutrients, heavy metals in both seeds and leaves, as well as the seed fatty acid composition, were analyzed. Additionally, soil nutrient contents were assessed post-experiment

Initially, HC application did not cause a noticeable change in soil nutrient composition. However, both HC applications demonstrated high productivity under well-irrigated conditions. Likewise, under WD conditions, the best yields were achieved with a HC dose of 6.5 t ha^-1. Conversely, the composition of the different fatty acids in the seed oil remained unaffected by the treatments and irrigation conditions. Nonetheless, seed nutrient content was notably affected, particularly in plants treated with 6.5 t ha^-1. Under well-irrigated conditions, the seeds of these plants exhibited decreased K and P levels, along with higher levels of toxic elements and heavy metals such as Al, Ba, Cd, Pb, and Sr. Under WD conditions, the impact of the treatment on heavy metals contents was less pronounced, but there was a marked reduction of seed macronutrient content (Ca, K, Mg, P and S). Notably, plants treated with 6.5 t ha^-1 of HC under well-irrigated conditions exhibited a preferential accumulation of Al and Sr in the seeds, leading to the lowest concentrations of these toxic elements in their leaves. The accumulation of these metals in the seeds was accompanied by a decline of both elements in the soil after 77 days of experiment under this irrigation condition, suggesting plant uptake. Given that the concentration of both elements did not increase after the application of HC at the beginning of the experiment, it is presumed that these changes are due to a potential role of HC involved in heavy metals mobilization. Following qPCR analysis this may be related to microbial activity since the soils treated with 6.5 t ha^-1 of HC exhibited a higher abundance of 16S rRNA and ITS gene copies related to bacteria and fungi, respectively, along with an increased dehydrogenase activity. Our findings highlight that the impact of char amendment on soil systems should not be seen as a simple linear process but has to be evaluated considering the complex interactions between climatic conditions, application rate, plant physiology and microbial activity.

How to cite: Moreno Racero, F. J., Reinoso, R., Gismero Rodríguez, L., Martínez Force, E., Rosales Villegas, M. Á., and Knicker, H.: The application of hydrochar promotes soil microbial growth and enhances sunflower yield, altering the nutritional composition of the seeds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-591, https://doi.org/10.5194/egusphere-egu24-591, 2024.

Forest soils and roots harbor hyper-diverse microbiomes which strongly shape the growth and development of plant communities. How the biodiversity and functional capacities of the microbiome influence emergent ecosystem functioning is an important next frontier in the biogeosciences with implications for conservation, ecosystem management, and microbiome engineering. Directly testing hypotheses between microbiome diversity and forest functioning has been obstructed by a lack of paired data on microbiomes and in situ observations of forest growth and health. Here, I will synthesize findings from two large-scale European forest soil and root sampling efforts where we identified features of the mycorrhizal fungal, soil fungal, and bacterial communities linked to variation in forest tree growth and nutrition. We sampled roots and/or soils across 285 forest monitoring plots spanning 18 European countries, sequenced full-length fungal ITS and prokaryotic 16S amplicons to relate microbiomes to high resolution observations of tree growth, foliar nitrogen and phosphorus content, and aboveground carbon stocks. We show that the composition, richness, and traits of both root and soil inhabiting symbiotrophic fungal guilds is tightly linked to variation in tree growth, nutrition, and aboveground biomass carbon stocks while the biodiversity of free-living microbiomes was not tightly coupled to these key metrics of aboveground forest functioning. We also produced a roster of fungal biodiversity and compositional traits which are strong positive and negative bioindicators of forest carbon storage and nutrition. These large-scale observations lay important groundwork for experimental studies and demonstrate that soil microbiomes capture unique variation in emergent forest functions that cannot be explained by other physical, chemical, and biological properties.

How to cite: Anthony, M. A. and the ICP Forests Microbiome Collaboration: Forest microbiomes and aboveground forest functioning , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1765, https://doi.org/10.5194/egusphere-egu24-1765, 2024.

Glucose is one of the major primary metabolites in the plant root exudates to mediate the cross-talk between plants and microbes, but their contribution to drought resistance of plants is largely unknown. To test this, we inoculated arbuscular mycorrhizal fungi (AMF) in soybean, quantified rhizospheric microbial hotspots, visualized glucose exudation pattern, and analyzed microbial activities, such as kinetic properties of β-glucosidase and acid phosphomonoesterase enzymes, and microbial biomass phosphorus.

Drought reduced glucose exudation, mainly allocated to root tips under optimum conditions, and narrowed the rhizosphere enzymatic hotspot by three times. However, AMF inoculation enhanced glucose exudation compared to non-mycorrhizal plants, and enlarged enzymatic hotspot area by 53% under drought condition. Despite the 50% reduction in β-glucosidase and acid phosphomonoesterase activities owing to water deficit, AMF symbiont triggered up to 36% enzyme activities in correlation with the non-mycorrhizal ones. Therefore, the drought resistance of these two enzymes was enhanced by up to 63% in mycorrhizal plants. The biomass of microbial phosphorus increased by 45% under drought conditions in plants inoculated with AMF.

Overall, the greater resistance of enzyme activities to drought in AMF-inoculated than in non-mycorrhizal suggest that microorganisms associated with mycorrhizal root have higher capability to react to altered abiotic environmental conditions than those associated with non-mycorrhizal roots. The mycorrhization induced an interactive regulation of soybean glucose exudation and rhizosphere expansion for enzyme activities. This contributed to the resistance of microbial functions (e.g., enzyme expression) to drought stress in AMF-inoculated than in non-mycorrhizal soybean. AMF-inoculation suppressed adverse drought effects on plant and microbial nutrient mining, which has substantial implications for controlling microbial roles in organic matter decomposition and P cycling.

Keywords: glucose imaging, arbuscular mycorrhiza fungi, soybean, hotspot, drought resistance

How to cite: Hoang Thi Thu, D.: Overlapping locality between rhizosphere and mycorrhizosphere regulates glucose exudation pattern in rhizosphere and enzyme distribution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1017, https://doi.org/10.5194/egusphere-egu24-1017, 2024.

For decades, biogeochemists have speculated that roots are key drivers of anoxic microsites – anomalous volumes of oxygen depletion – in upland soils. Rhizosphere-associated anoxic microsites are hypothesized to regulate plant contaminant uptake, nutrient availability, and the fate of root-derived carbon. However, despite the potential importance of rhizosphere-associated anoxic microsites, it remains unclear why, when, and where anoxic microsites form in the rhizosphere. Here, we pair planar optical oxygen sensors with microfluidic devices mimicking a soil structure to map the distribution of oxygen in a young wheat rhizosphere. We filled microfluidic devices with i) sterile; ii) wheat symbiont-inoculated, and iii) whole-soil community-inoculated nutrient solutions. As a result, we were able to determine root oxygen consumption vs. microbial oxygen consumption over space (i.e., at different root physiological features) and time (i.e., day/night cycles). We will show that i) intense root respiration within the root tip may drive anoxic microsite formation, even in the absence of microbial respiration; ii) microbial colonization of lateral root emergence may drive localized oxygen depletion in older root sections, and iii) overall rhizosphere oxygen depletion has a predictable, diurnal cycle dictated by the plant’s photosynthetically active period. Our findings are the first to link root physiology to anoxic microsites, providing a strong basis for future studies of anoxic microsites in field soils. 

How to cite: Lacroix, E., Ceriotti, G., Garrido-Sanz, D., Borisov, S., Berg, J., Keel, C., de Anna, P., and Keiluweit, M.: Why, where, and when are there anoxic microsites in the rhizosphere – a microfluidic approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6598, https://doi.org/10.5194/egusphere-egu24-6598, 2024.

Landfills are one of the largest anthropogenic sources of methane (CH₄), and hot-spots of CH₄ emissions in landfill cover soils can enrich microbes that oxidize CH₄ to carbon dioxide (CO₂). CH₄ oxidation rates are modulated by multiple variables including soil moisture and temperature, although the interactive effects of these factors on CH₄ oxidation rates have not been well-studied. Here, we conducted a closed-headspace batch experiment with cover soil from a former landfill in Ontario, Canada to measure CH₄ consumption and CO₂ efflux rates associated with variations in soil moisture and temperature simultaneously. Soil samples were incubated under a factorial design of 5 soil moisture contents ranging from 11 to 47% WFPS (water-filled pore space), and 6 temperatures ranging from 1 to 35°C. At each temperature and WFPS combination, CH₄ (812 nmol) was spiked into the headspace, and headspace CH₄ and CO₂ concentrations were measured over 2 hours to calculate CO₂ efflux and CH₄ consumption rates. The maximum CO₂ efflux rate was observed at the maximal WFPS and temperature conditions of this experiment (92 nmol h^-1 g dry wt.^-1 at 47% WFPS and 35°C), while the maximum CH₄ consumption rate was observed at intermediate WFPS and temperature conditions (1.9 nmol h^-1 g dry wt.^-1 at 25% WFPS and 25°C). The CO₂ efflux observed is primarily attributed to the oxidative degradation of soil organic matter. A diffusion-reaction model was fit to the observed data to represent the effects of temperature and soil WFPS on the CH₄ consumption and CO₂ efflux rates. The model predicted similar optimal conditions as those observed for both the CH₄ consumption and the CO₂ efflux rates. The modeling and experimental results show that the dominant controls on optimal soil moisture for CH₄ consumption are moisture limitation of microbial activity and of gas (CH₄ and oxygen) diffusion, versus the interactive effects of moisture limitation of gas (oxygen) diffusion and of solute mobility for CO₂ effluxes. These results provide insight into how seasonal changes in soil moisture and temperature could impact CH₄ oxidation rates, and therefore also net CH₄ emissions, in landfill cover soils and other environments.

How to cite: Lam, C., Slowinski, S., Ramezanzadeh, M., Hug, L., Willms, N., Van Cappellen, P., and Rezanezhad, F.: Consumption of methane by a landfill cover soil under variable moisture and temperature conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13836, https://doi.org/10.5194/egusphere-egu24-13836, 2024.

The response of soil carbon release to global warming is largely determined by the temperature sensitivity of soil respiration, yet how this relationship will be affected by increasing atmospheric nitrogen deposition is unclear. Here, we present a global synthesis of 686 observations from 168 field studies to investigate the relationship between nitrogen enrichment and the temperature sensitivity of soil respiration. We find that the temperature sensitivity of total and heterotrophic soil respiration increased with latitude. In addition, for total and autotrophic respiration, the temperature sensitivity responded more strongly to nitrogen enrichment with increasing latitude. Temperature and precipitation during the Last Glacial Maximum were better predictors of how the temperature sensitivity of soil respiration responds to nitrogen enrichment than contemporary climate variables. The tentative legacy effects of paleoclimate variables regulate the response through shaping soil organic carbon and nitrogen content. We suggest that careful consideration of past climate conditions is necessary when projecting soil carbon dynamics under future global change.

How to cite: Tian, P.: Past climate conditions predict the influence ofnitrogen enrichment on the temperature sensitivityof soil respiration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1953, https://doi.org/10.5194/egusphere-egu24-1953, 2024.

Hotspots are characterized by an increased availability of nutritional elements compared to the surrounding bulk soil, which enhances microbial activity. However, the shifts in nutrient stoichiometry, when hotspot formation is initiated by a non-microbial organic matter source (rhizodeposits, litter, feces & mucus, percolating dissolved organic matter), are highly hotspot-specific. This results in contrasting microbial dynamics in the rhizo-hyphosphere, the detritusphere, the drilosphere and further biopores of soil animals, and in preferential flow pathways.

Experiments and models of microbial growth-death dynamics have recently improved our understanding of how element stoichiometry shapes element allocation in microbial metabolism. This holds specifically true for to the two contrasting pathways of microbial growth – intracellular element storage versus the investment of C, nutrients and energy in replicative microbial growth. Both growth modes involve synthesis of organic polymers – either storage or structural cellular polymers. However, the nature of these two types of polymers is highly contrasting with regards to their elemental but also their molecular diversity, such that the two growth modes generate distinct differences in the molecular compositon of the cellular biomass. We can therefore expect that the stoichiometric differences of nutrient hotspots will drive differences in the molecular diversity of the microbial biomass, and so ultimately the successively accumulating necromass.

Whereas controlled incubation experiments demonstrate how element allocation to storage and replicative growth depends on nutrient stoichiometry, we lack an understanding of how growth modes are distributed among hotspots in situ. Besides developing this conceptual understanding, we aim to shed light on the implications of differences in cell physiology among hotspots, which includes i) the turnover rate of microbial biomass due to contrasting resistance to stress (e.g. starvation), ii) the molecular composition of the microbial cells and iii) the resulting chemical properties and molecular diversity of necromass. These factors strongly influence the formation rates, qualities and persistence of necromass-derived soil organic matter arising in these hotspots. Furthermore, the accrual of organic matter shapes microbial resource availability, including element stoichiometry, in the hotspot, as well as the physico-chemical microbial habitat properties. In consequence, a feedback loop between microbial growth- and turnover-based organic matter formation and the initial processes, that trigger the hotspot formation elaborates. Thus, although hotspot formation is always initiated by non-microbial organic matter input, the characteristics of the established soil hotspots are ultimately linked to the microbial necromass’ molecular and elemental diversity, which is the direct product of the hotspots’ microbial metabolism and growth mode. This study aims to relate the nutrient enriching processes (rhizodeposits, litter, feces & mucus, percolating DOM) and soil-intrinsic feedbacks to the dominant microbial growth modes and resulting properties of the organic matter in soil hotspots. 

How to cite: Dippold, M. A., Banfield, C. C., and Mason-Jones, K.: Metabolic responses to hotspot-forming processes: growth modes and their ecological consequences, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13344, https://doi.org/10.5194/egusphere-egu24-13344, 2024.

Microorganisms are the primary agents of litter decomposition in the detritusphere, and are considered potentially powerful levers for influencing soil biogeochemical transformation of plant C into soil organic matter (SOM). However, it remains unclear whether soil microbial activity is primarily constrained by the microbial community composition or by the abiotic soil habitat in which they live. We explored the relative importance of abiotic and biotic factors in litter carbon (C) cycling by reinoculating five sterilized agricultural soils from the Netherlands with six contrasting soil microbial communities from a gradient of land-use intensity. Admixing of subsurface horizons (representing older SOM) and the addition of synthetic ferrihydrite (as an iron oxide representative) were included as additional abiotic manipulations. 16S and ITS amplicon sequencing confirmed that the contrasting communities successfully colonized the sterilized soils and retained strong signatures of their source inoculum during a laboratory incubation of nine months. Nevertheless, basal respiration of SOM and the mineralization of isotopically (¹³C) labelled litter (Lolium perenne) was overwhelmingly determined by the abiotic soil matrix, most notably the source soil and mixing of subsurface horizons. Ferrihydrite, in contrast, had little effect. These observations were extended by quantification of mineral nitrogen as well as ¹³C incorporation into particulate and mineral-associated SOM fractions. The findings provide strong experimental support for the responsiveness of C cycling to soil abiotic habitat factors, irrespective of community structure.

How to cite: Mason-Jones, K., Ingenhoven, K., Hannula, S. E., Veen, G. F. (., and van der Putten, W. H.: Abiotic soil matrix, rather than microbial community composition, determines litter C cycling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13285, https://doi.org/10.5194/egusphere-egu24-13285, 2024.

Arbuscular mycorrhizal fungi (AMF) affect both plant nutrition and soil physical properties, including soil water retention and hydraulic conductivity. However, much less is known about the preferences of AMF for proliferation into soils of different (physical) natures, i.e. soil textures. To investigate this, we designed a pot trial with tomato in which AMF had access to root-free soil patches of different textures. We hypothesized that AMF would prefer fine-textured soils over coarse-textured soils because a finer textured soil is comparatively moist (which most fungi prefer) and contains a greater share of low-weight particles (less growth resistance) than a coarse-textured soil.

We inoculated tomato plants with the fungus Rhizopagus irregularis grown in 4L pots filled with a quartz sand: loam mixture (1:1 w/w). The loam is a calcareous alluvial loam obtained from the C-horizon with a pH of 7.5, low in organic matter (0.05% C_org), 42.72% sand, 44.22% silt, 13.06% clay and is highly P-fixing. The self-propagated fungal inoculum used was based on this loamy soil and, therefore, inoculation did not compromise the soil texture of the potting mix. Each pot received three ingrowth cores covered in root-excluding nylon mesh (37 µm) containing either pure quartz sand (grain size 0.3 – 1.0 mm), pure loam soil or a 1:1 mixture of the two (as in the main pot). To cause variance in soil hyphae development, we applied two treatments. On the one hand, half of the pots contained the tomato cultivar 76R and the other half its related rmc mutant, which is known to show reduced mycorrhizal colonization. On the other hand, we subjected half of the pots to two weeks of terminal drought to slow down plant and fungal growth, while the other half of the pots were kept under ample moisture. After harvest, we measured root colonization and plant nutrient uptake to verify the viability of the mycorrhizal symbioses. From the ingrowth cores, we extracted AMF hyphae and determined their length. As traits known to be affected by functional hyphae and plant activity as well as soil desiccation, we also measured aggregate stability indices in soils from the ingrowth cores.

According to our expectations, we found that the 76R tomatoes, which were able to develop a viable symbiosis, had higher tissue P and N mass fractions in their dry matter than the rmc tomatoes.  Against our expectations, the 76R plants were more sensitive to drought when exposed to it and had significantly lower biomass than the rmc plants and the 76R plants maintained under ample moisture. Furthermore, we illustrate our findings on hyphal length density and aggregation and discuss them with regard to the preferences of AMF to populate the soils with different textures. We answer whether our hypothesis must be confirmed or denied and deduce some potential ecological consequences of our findings.

How to cite: Jacob, E., Camenzind, T., and Bitterlich, M.: The modulation of plant nutrition and soil properties by mycorrhizal fungi and their preferences for the soil texture they encounter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15871, https://doi.org/10.5194/egusphere-egu24-15871, 2024.

Soils are the largest and most dynamic carbon reservoir in terrestrial environments, with most carbon stored as mineral-associated organic matter (MAOM). It has recently been shown that MAOM is effectively destabilized by reactive compounds released by plant roots and associated microbes. It is well known that quantity and quality of rhizodeposits dramatically change in response to nutrient or water stress, with unclear consequences for rates of plant root-driven MAOM destabilization. Here we show that altered rhizodeposition in response to environmental stressors affects rates of root-driven MAOM destabilization. Well-controlled growth chamber experiments with Avena sativa (common oat) allowed us to test the individual and interactive effects of nitrogen, phosphorus, and water limitations on the fate of 13C-labeled MAOM over a 10-week period. At the end of the experiment, total MAOM mineralization was strongly correlated with root biomass, which generally declined with nutrient and water limitations. However, under P limitations, root-driven MAOM mineralization was greatest during the initial growth stages (vegetative), whereas N limitations resulted in greater rates of MAOM mineralization during later growth stages (flowering). Drought treatments, when compared to their corresponding optimal watering treatments, produced the least MAOM destabilization. To test whether temporal changes in MAOM destabilization rates can be explained by differences in rhizodeposition intensity and composition, we analyzed rhizodeposits collected throughout the experiment via high-resolution mass spectrometry. This study demonstrates that MAOM mineralization is regulated not just by the inherent stability of MAOM against microbial attack, but also depends on plant water and nutrient availability within the whole plant-soil system as well as plant physiological and phenological stages. Through such feedback, changes in soil nutrient and water status (e.g. via altered precipitation or fertilizer application) can be expected to cause plant-induced alterations to the size of the otherwise stable, mineral-associated soil carbon reservoir.

How to cite: Keiluweit, M., Garcia Arredondo, M., Castro, S., Tfaily, M., and Cardon, Z.: Nutrient and Water Availability Modulate the Destabilization of Mineral-Associated Organic Matter in the Rhizosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16663, https://doi.org/10.5194/egusphere-egu24-16663, 2024.

The rapid growth of metallic nanoparticles (such as ZnO) in the present time increases the risk of the contamination of soil because it is the sink for all the nanoparticles, intentionally or unintentionally, and affects the microorganism productivity and damages the soil health. Zinc oxide nanoparticles are widely used in agriculture and other industries at the current time. Our study aimed to evaluate the toxicological effects of zinc oxide nanoparticles on the bacterial diversity of soil. A microcosm experiment was conducted by mixing the 1000 µg/gm of ZnO nanoparticles in the soil. After 60 days, the effect of zinc oxide nanoparticles on bacterial diversity was determined using Illumina MiSeq sequencing of 16S rRNA genes. The soil's physiochemical characteristics, such as C, H, and N content, were analyzed and compared with non-treated samples. Dehydrogenases (DH) and fluorescein diacetate (FDA) were assayed as the soil health indicator.  Results have shown that the relative abundances of the dominant and agriculturally significant phyla, namely, Proteobacteria and Actinobacteria, were altered in the presence of Zinc Oxide nanoparticles. However, it was also observed that Zinc oxide nanoparticles showed negligible effects at the phylum level. The dissolution of ZnO nanoparticles was also estimated with the help of ICP-MS, which was 870 µg/gm after 60 days. DH activity was higher and FDA activities were lowered compared to the non-treated soil.

How to cite: Javed, Z., Tripathi, G. D., and Dashora, K.: Effect of ZnO nanoparticles on the bacterial community and other soil health parameters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20825, https://doi.org/10.5194/egusphere-egu24-20825, 2024.

Bacillus megaterium is a plant growth-promoting bacteria that performs various activities like producing hydrolytic enzymes in the soil such as protease and xylanase, releasing various growth hormones and other bioactive compounds that inhibit the plant pathogenic microbes in the soil. These microorganisms are not only part of the rhizosphere but instrumental in activities such as soil conditioning and nutrient cycling. But as the modernization of agriculture practices comes up with new age agrochemicals, called nano-agrochemicals, the concerns of toxicity also increased. These nano agrochemicals (such as CuO nanoparticles) have several advantages over the traditional chemicals, however, several properties like small size, lower dissolution, and potential to alter soil properties such as pH, raise serious threats to the soil beneficial microbes. It is also estimated that the accumulation of nanoparticles in the soil may become available for microbial ecosystems and cause toxicity with unique mechanisms, eg contact mode toxicity. Copper oxide nanoparticles are integral to new-era agrochemicals like nano-pesticides, nano-fertilizers, etc. There are mixed reviews on the toxicity of CuO nanoparticles on soil owing to diverse microbiota. Our in vitro studies were focused on the analysis of the size and dose-dependent impact of nanoparticles on the plant growth-promoting species  Bacillus megaterium at cellular, morphological as well as Indole acetic acid (IAA) production potential. Our study reveals that the small dose (0.05mg/ml) of copper oxide is not harmful to the microbes because copper is one of the essential elements However at upper concentration around 0.5mg to 1 mg/ml was significantly toxic for the Bacillus megaterium. The size-dependent toxicity on IAA production was also tested with the two different sizes of the CuO nanoparticles and the results were not significantly different.  

How to cite: Tripathi, G. D., Javed, Z., and Dashora, K.: Impact of Copper oxide nanoparticles on soil isolated Bacillus megaterium  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20849, https://doi.org/10.5194/egusphere-egu24-20849, 2024.

The ongoing change in climate extensively alters belowground interactions between plants and microbiota. Alterations in plant-microbiota interactions have significant implications for the functioning of ecosystems. To predict ecosystem change and protect vulnerable systems, it is therefore crucial to understand how climate shapes belowground plant-microbiota interactions. We test how prokaryote and fungal rhizosphere and root-associated communities of the perennial grass Festuca rubra are affected by temperature and precipitation in cold climate settings. We found that microbial communities were strongly shaped by temperature and to a lesser extent by precipitation. Temperature decreased relative habitat specialisation of the rhizosphere community and the fungal root-associated community. These effects were mediated by an increase in forb cover and a decrease in soil pH with temperature. Our findings indicate that with a rise in temperature in cold environments, plant-microbiota interactions become more versatile and adapted to a broader range of environmental conditions.

How to cite: in 't Zandt, D., Aldorfová, A., Šurinová, M., in ‘t Zandt, M. H., Vandvik, V., and Münzbergová, Z.: Temperature increases the versatility of belowground plant-microbiota interactions in cold climates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16883, https://doi.org/10.5194/egusphere-egu24-16883, 2024.

The cyanosphere contains heterotrophic microorganisms living within the exopolysaccharide sheath of cyanobacteria and serves as an interface between the cyanobacteria and their surrounding ecosystem. The symbiosis between the cyanobacterial host and its cyanosphere microbes spans the mutualistic-antagonistic spectrum. Understanding these relationships will predict the success of terrestrial cyanobacteria and the ecosystem services they provide including primary production in often oligotrophic environments. However, our understanding of the microbial diversity within the cyanosphere is limited. In this study, we used metagenomic sequencing to construct 528 metagenome-assembled genomes (MAGs) from the cyanosphere microbes associated with 50 unialgal terrestrial Cyanobacteria cultures, spanning 12 orders. We found that the composition of cyanosphere microbial communities was unique between Cyanobacteria hosts and was largely influenced by environmental (habitat, precipitation, and temperature) and phylogenetic variables (host order). Alphaproteobacteria was the most common cyanosphere microbial class and Bosea, Devosia, Hyphomicrobium, Mesorhizobium, and Sphingomonas were core genera found across all habitats. Interestingly, the nitrogen-fixing cyanobacterial order, Nostocales, contained the highest diversity of cyanosphere bacteria, many of which have the genomic potential also to fix atmospheric nitrogen. Given the observed variations in the cyanosphere microbial communities across different hosts, future considerations for ecological assessments and cyanobacterial restoration efforts must extend beyond the cyanobacteria to encompass their associated microbial communities.

How to cite: Pietrasiak, N., Palmer, B., Couradeau, E., and Stajich, J.: Revealing cyanosphere microbial diversity of terrestrial cyanobacteria, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14182, https://doi.org/10.5194/egusphere-egu24-14182, 2024.

The Australian rangelands that cover around 70% of the country (~6 million km²) are inhabited by some of the most extensive and diverse biocrusts globally. These regions are predominately managed as natural grazing lands. Across northern Australia where the climate is influenced by the monsoon (wet season) biocrusts dominated by cyanobacteria and liverworts occupy the interspaces between grass plants as a coherent layer that binds the upper millimetres of soil and forms a living cover of photoautotrophic (cyanobacteria, algae, lichens and bryophytes), and heterotrophic (bacteria, fungi and archaea) organisms. During the dry season biocrusts are inactive, then recover at the onset of the wet season, actively participating in nitrogen and carbon fixation and accumulation. To identify the role of biocrusts as ecological indicators, we modelled their distribution, diversity and function across microhabitats. We also determined how biocrust community dynamics had been influenced by long-term fire and grazing management regimes.

At Victoria River Research Station (Kidman Springs, NT), after 30 years of fire research we compared managed burning practices at 2, 4 or 6-yearly intervals on two soil types (calcarosol, vertosol). Biocrusts were resilient and recovered rapidly from fire, where diversity and genetic function altered seasonally, between soil types, and fire regimes. Post-fire, after a wet season (cattle excluded), biocrusts recovered with significantly more carbon and nitrogen in the surface soils of cooler fire treatments every four years.  

At Wambiana Cattle Station (QLD), grazing trials have been established for 25 years. When paddocks were rested from cattle grazing every second year, biocrusts in duplex soils recovered to levels comparable to ungrazed natural sites. In red-yellow earths, there were biocrust hotspots that provided protection to the soil surfaces when there was a loss of grass cover during drought. Biocrust diversity and function differed between soil type and management (moderate and heavy stocking).

This research demonstrates that the top centimetre of biocrust-rich soil is central to ground cover integrity and is essential to soil nutrient cycling and fertility. Biocrusts are an important indicator for overall vegetative recovery post fire, grazing and drought disturbances. The principles of land cover condition based on landscape function should include biocrust presence as a metric that describes landscape resilience, as opposed to bare unprotected ground. Importantly, land managers can apply this research to grazing practices that show that giving the land rest periods timed to coincide with the wet season allows time for biocrust organisms to recover from disturbance.

How to cite: Williams, W., Myint Swe, T., Vega, M., Driscoll, C., Cowley, R., O’Reagain, P., Potgieter, A., Zhao, Y., Dennis, P., and Schmidt, S.: Biocrusts, ecological indicators in the Australian rangelands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21779, https://doi.org/10.5194/egusphere-egu24-21779, 2024.