Droughts significantly impact forests, with long-term forest existence largely depending on seedling recruitment. However, seedling establishment under natural conditions is often limited by numerous interacting factors such as water availability, competition with herbaceous vegetation, and interaction with ectomycorrhizal fungi (EMF). We performed two greenhouse experiments to examine these factors and their interacting effects on the establishment of Aleppo pine seedlings. In both experiments, Geopora, a genus known to colonize seedlings in dry habitats, predominantly colonized the seedlings' roots, regardless of the EMF inoculum's origin. EMF inoculation enhanced seedling height, biomass, and branch number. However, under combined drought and competition, EMF had no growth impact. When facing competition or consistent water scarcity, EMF's positive effects decreased. Interestingly, during intermittent drought periods (resource pulses), EMF benefits persisted even in severe drought. This discrepancy in pine performance across treatments highlights the complexity of benefits provided to seedlings by EMF under ecologically relevant settings.

How to cite: Livne- Luzon, S., Herol, L., Klein, T., and Shemesh, H.: Context-dependent benefits of ectomycorrhiza on Aleppo pine seedling performance under ecologically relevant settings , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5313, https://doi.org/10.5194/egusphere-egu24-5313, 2024.

Increasing industrial activity has led to a growing risk of cadmium (Cd) accumulations and biomagnifications in plants and humans. Arbuscular mycorrhizal fungi (AMF) have been extensively studied as a soil amendment technique due to their capability to reduce the accumulation of Cd in plant tissues. However, a quantitative and data-based consensus has yet to be reached on the effect of AMF on host plant growth, Cd uptake, and tolerance. Here, a meta-analysis was conducted to quantitatively evaluate the impact of AMF using 2079 individual observations from 157 articles. The research showed that adding AMF to the plants stopped the accumulation of Cd in the shoots and roots and increased biomass, phosphorus (P), and catalase (CAT) in the leaves compared to the control. Yet these effects varied with different mycorrhizal colonization rates, AMF species, plant families and functional types, and soil Cd contents. Mycorrhizal colonization rates positively correlate with changes in biomass and P content in shoots and roots, and CAT and proline in leaves, while showing no significant correlation with Cd concentration in plant tissues. Plants inoculated with Funneliformis caledonium exhibited greater biomass accumulation, while those inoculated with Rhizophagus irregularis showed higher P uptake. Mycorrhizal Legumes demonstrated the most significant reduction in Cd concentration among the plant families, whereas Compositae exhibited the highest increase in biomass, P content, and CAT. In addition, soils with intermediate and high Cd levels were more favorable for AMF to promote plant biomass accumulation. This study shows that AMF can help plants become more resistant to environments with excessive Cd. It also talks about how to manage and use them as bio-inoculants for farming and environmental restoration.

Acknowledgments

This research received funding from the National Key Research and Development Program of China (No. 2022YFC3701303) and the National Natural Science Foundation of China (Grant Nos. U2344228).

How to cite: Tan, Q., Wei, R., Hu, H., and Guo, Q.: Role of arbuscular mycorrhizal fungi behind the plant ameliorated tolerance against cadmium stress: A global meta-analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6946, https://doi.org/10.5194/egusphere-egu24-6946, 2024.

Microbes are responsible for the cycling of carbon (C) in soils, and predicted changes in soil C stocks under climate change are highly sensitive to shifts in the mechanisms thought to control microbial physiological response to warming. Two mechanisms have been proposed to explain the long-term effects of warming on microbial physiology: microbial thermal acclimation and changes in the quantity and quality of substrates available for microbial metabolism. However, studies disentangling these two mechanisms and assessing how land use affects them are lacking. To disentangle the drivers of changes in microbial physiology in response to long-term climate change, we sampled soils from a 10-year old global change and land use intensity experiment at the Pre-Alpine Terrestrial Environmental Observatories (TERENO project). The global change treatment includes a warming of 2^oC and a reduction in precipitation of about 450 mm. We took soil samples at different time-points during the spring season and depths. We performed short-term laboratory incubations over a range of temperatures to measure the relationships between temperature sensitivity of physiology (growth, respiration, carbon use efficiency with the ¹⁸O-H₂O method) and we characterized the quantity and quality of soil organic matter with the ramped thermal rock-eval pyrolysis at different depths. In this ongoing project, we did not observe thermal acclimation of microbial respiration, growth or CUE to climate change. However, fertilization had the strongest effect on the temperature sensitivity of microbial respiration. In the next steps of this project, we will determine whether climate change and/or land use intensity has an effect on soil organic carbon fractions with different residence times. Our preliminary results show that land use intensity has an overriding effect on the temperature sensitivity of microbial processes compared to long-term climate change.

How to cite: Domeignoz-Horta, L., McLaughlin, M., Soares Fontes, M., Sebag, D., Aubertin, M.-L., Verrecchia, E., Kahmen, A., Nelson, D., Laine, A.-L., Niklaus, P., Butterbach-Bahl, K., and Kiese, R.: Land use intensity has a stronger effect on the temperature sensitivity of soil microbial carbon cycling processes than long-term climate change., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16307, https://doi.org/10.5194/egusphere-egu24-16307, 2024.

Permafrost soils are particularly vulnerable to climate warming. With ~1,500 Gt Carbon (C), they store a significant proportion of global soil C. Organic matter that was frozen and thus unavailable for microbial decomposition for millennia, is now thawing. How much of this permafrost C is decomposed will be determined by microbial activities and the partitioning of assimilated C to microbial growth (potential C stabilization) or microbial respiration (C loss). Our current knowledge on the controls of microbial growth and respiration in permafrost soils is, however, limited.

The objective of this study was to analyze microbial growth and respiration in permafrost soils and to explore soil organic matter composition, microbial community composition and various soil parameters as potential drivers. We collected 81 soil samples from four soil layers (organic, mineral, cryoturbated, permafrost) and three lowland tundra polygon types (low-center, flat-center, high-center) in Arctic Canada. We used pyrolysis-GC-MS fingerprinting to characterize soil organic matter composition and amplicon sequencing (16S, ITS1) to identify archaeal, bacterial, and fungal community composition. Temperature responses (Q₁₀) were analyzed in an 8-week laboratory incubation experiment, subjecting soil aliquots to 4 °C and 14 °C. Microbial growth was determined by ¹⁸O-H₂O-incorporation into DNA and microbial respiration by gas analysis.

Soil organic matter composition differed between soil layers along a gradient of degradation and C content. Organic matter complexity and diversity decreased with the level of decomposition. We found distinct soil organic matter composition for each polygon type, including all soil layers, suggesting different decomposition pathways, induced by differences in vegetation and soil water regime. Anoxic conditions in low-center polygons resulted in more archaea and distinct fungal communities. Microbial community composition differed among all soil layers, with particularly more fungi in organic soils. Microbial mass-specific growth and respiration differed among polygons and soil layers, and both increased with warming. Overall, temperature responses (Q₁₀) were higher for respiration than for growth, implying that microbes are less efficient in using C for growth. Linear mixed effect models revealed that soil organic matter composition and microbial community composition were good predictors for mass-specific growth at field and warmed conditions. Mass-specific respiration was best explained by microbial community composition. Our predictors, however, did not explain the temperature responses.

Our results indicate that under warming, microbes allocated more C to respiration, leading to increased greenhouse gas emissions per unit of carbon taken up. We found these results while including all soil layers and polygon types, suggesting these responses to be representative for lowland Arctic ecosystems. Moreover, we could show that organic matter composition and microbial community composition are good predictors for microbial growth and respiration, thus deserving more attention in future studies.

This study is part of the EU H2020 project “Nunataryuk”.

How to cite: Rottensteiner, C., Martin, V., Canarini, A., Schmidt, H., Jensen, L., Horak, J., Mohrlok, M., Urbina Malo, C., A'Campo, W., Durstewitz, L., Wagner, J., Lodi, R., Speetjens, N., Tanski, G., Fritz, M., Lantuit, H., Hugelius, G., and Richter, A.: Microbial growth in a warming Arctic: Exploring controls and temperature responses in permafrost soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19132, https://doi.org/10.5194/egusphere-egu24-19132, 2024.

As global temperatures rise, soil fractions of organic matter are being subjected to microbial degradation, particularly in high latitude regions.  Concurrently, permafrost perched below active layer soils is thawing at unprecedented rates, significantly altering landscapes and ecosystem trajectories by changing subsurface conditions and vegetation characteristics. Our aim was to investigate an Alaskan soil microbiome’s response to changes in temperature and water potential because they are well established factors that influence microbial activity and could be predicted using remote sensing data and weather forecasts.  The extent of microbial change in the seasonally thawed active layer remains poorly understood.  To address this, we studied the physical and microbiological properties of two permafrost-affected surface soils in interior Alaska primarily composed of deciduous forests, coniferous forests, and woody wetlands.  We collected soils for laboratory incubation studies where we measured respiration and microbial taxonomy from replicate microcosms experiencing four temperatures and five matric potentials.  Soil respiration rates from the soils varied according to temperature and moisture, with soils exposed to warmer, wetter conditions exhibiting the highest respiration rates (e.g. 0.23 or 0.70 µg C-CO₂ g^-1 dry soil h^-1) and soils exposed to colder, drier conditions exhibiting lower respiration rates (e.g. 0.03 or 0.1 µg C-CO₂ g^-1 dry soil h^-1).   In the field, we measured soil temperature, moisture, and respiration at the sites where the soils were initially collected.  Surface soil temperatures measured at the sites ranged from -25°C in the winter months to +25°C in the summer months.  These values were compared to geospatial estimates of temperature and soil moisture that were used to calculate soil respiration rates.  The estimated respiration values will be compared to field measurements to determine the efficacy of the model.  Additionally, respiration estimates will be calculated under a future climate scenario.  These findings have important implications for developing accurate forecasts of microbial community assemblages during thaw in that location should be considered as a strong influencing factor. 

How to cite: Barbato, R., Doherty, S., Letcher, T., Vas, D., and Parno, J.: Comprehensive geospatial assessment of the soil microbiome’s response to temperature and moisture in interior Alaska, USA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6731, https://doi.org/10.5194/egusphere-egu24-6731, 2024.

Drought has long-lasting legacy effects on grassland ecosystem functioning, which can manifest as shifts in soil microbial community structure and function and plant productivity that persist long after a drought passes. Increasing drought intensity causes abrupt shifts in plant productivity, plant-soil carbon and nitrogen dynamics, and soil microbial communities. However, very little is known about the role that drought intensity plays in the formation of drought legacies, and in plant and microbial responses to a subsequent drought. In a two-year experiment, we studied soil legacies associated with drought intensity in two model grassland plant communities with contrasting resource acquisition strategies (i.e., a fast- and a slow-strategy community). In the first year of the experiment, communities experienced a gradient of increasing drought intensity from well-watered to severely drought-stressed. In the second year, we determined soil microbial community composition and function, and plant community above-ground biomass in response to a subsequent drought. We found that the drought in the first year affected soil prokaryote and fungal community composition, microbial network structure, and soil function in the following growing season, and these effects were dependent on the past drought’s intensity. Soil drought legacy effects significantly altered plant community resilience to the subsequent drought: increasing intensity of the initial drought reduced plant community productivity resistance in slow-strategy plant communities, and decreased productivity overshoot seven weeks after re-wetting in fast-strategy plant communities. Our study shows that drought intensity causes distinct legacies in soil microbial community composition and function and alters the resilience of plant productivity to subsequent drought.

How to cite: Oram, N. J., Praeg, N., Bardgett, R. D., Brennan, F., Caruso, T., Illmer, P., Ingrisch, J., and Bahn, M.: Drought intensity shapes legacy effects on grassland plant and soil microbial communities and their response to a subsequent drought, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15868, https://doi.org/10.5194/egusphere-egu24-15868, 2024.

Soil is a complex environment, where microorganisms play a crucial role in the maintenance of soil structure, nutrient cycling and thus soil quality, relevant for croplands productivity. Soil microbial activity, however, is largely determined by water availability, and both are affected by agricultural management. This study aims to investigate the impact of irrigation, i.e. different amount of water and application scheduling, on soil microbial biomass and functional structure of soil microbiome (number of microorganisms in various ecological-trophic groups) in a Mediterranean maize farm. In 2023, six irrigation treatments were applied in a maize farm located in the Mondego Agricultural Valey, centre region of mainland Portugal. The irrigation treatments included three different amounts of water per week applied with drip irrigation: i) 100 mm, the average optimal amount over the last 30 years, based on APSIM crop model), ii) 55 mm, selected to simulate water scarcity conditions, and iii) the amount recommended by the local farmers’ association, based on weekly weather forecast and water balance modelling (ranged between 24 mm and 66 mm over the study period). The water was applied once or split in two applications during the week in different treatments. Each treatment was applied in triplicated plots, each plot covering five maize rows and extending over 10 m length. Nine composite soil samples (0-15 cm depth) per treatment were collected immediately before and after the irrigation period (~ 6 to 17 weeks after sowing). The soil samples were analyzed in sterile conditions using solid growth media: Nutrient Agar, Agar-Agar, Jensens Medium, Soil Agar, and Czapek-Dox Medium. The serial dilutions of the samples were provided until the suspension contained a microorganism titer within the range of 10⁻³–10⁻⁵ CFU/mL. The content of general microbial biomass (Сmic) in the soil was determined using the rehydration method. The results show that after the irrigation period, Cmic increased between 14% to 48%. The number of different nitrogen fixing bacteria and ammonifiers (nitrogen-mineralizing bacteria) increased, whereas the number of micromycetes, spore forming bacteria, oligotrophic, and pedotrophic bacteria groups decreased in all the treatments, which are good indicators about soil quality. Generally, these changes are slightly higher in the treatments where irrigation was applied twice instead of once a week (e.g. 28-31% vs 20-34% increase in nitrogen fixing bacteria, and 33-50% vs 12-36% decrease in oligotrophic bacteria - often associated to nutrient-poor soils). This highlights the relevance of providing a more uniform soil moisture content over the crop season (through smaller amounts of water, applied more often) to support soil microbial communities. Microbial biomass was lowest in plots receiving the less water (55 mm per week), but it was similar between plots receiving 100 mm of water per week and adjusting the amount of water to the recommendations of local farmers’ association. Long term average data would be useful to support decision on the amount of water to apply in areas where technical recommendations are not available. Adequate irrigation management in croplands can support soil biodiversity.

How to cite: Ferreira, C. S. S., Soares, P. R., Pereira, A., Mendes-Moreira, P., and Symochko, L.: Short-term impact of irrigation on soil microbiome in a Mediterranean maize cropping system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1653, https://doi.org/10.5194/egusphere-egu24-1653, 2024.

The severity of drought is predicted to increase across Europe due to climate change. Droughts can substantially impact terrestrial nitrogen (N) cycling and the corresponding microbial communities. Here, we investigated how ammonia-oxidizing bacteria (AOB), archaea (AOA), and comammox (complete ammonia oxidizers) respond to simulated drought in a rain-out shelter experiment in the DOK long-term field trial comparing different organic and conventional agricultural practices since 1978. This study is part of the MICROSERVICES (BiodivERsA) project aiming to understand and predict the effects of climate change on crop-associated microbiomes and their ecosystem functions. We monitored the diversity, the composition, and the abundance of ammonia-oxidizers for five months by Illumina-based amplicon sequencing and quantitative real-time PCR using the amoA gene as molecular marker.

We found that the effect of drought varied depending on the ammonia-oxidizing community and also on the agricultural practices. The community structures of AOA and comammox were more strongly affected by drought than the AOB community structure. Drought also had a stronger impact on the community structure in the biodynamic (organic) cropping system than in both the mixed and mineral-fertilized conventional systems. The abundance of ammonia oxidizers was also influenced by drought, with comammox clade B exhibiting the strongest sensitivity to drought. The drought effect on the community abundance was more prominent in the biodynamic and mixed-conventional systems than in the mineral-fertilized conventional system. We further found a significant interaction between drought and agricultural practices on the abundance of all groups of ammonia-oxidizers except AOB. Overall, our study showed that the impact of drought on ammonia oxidizers was modulated by agricultural practices and varied with time as well as among members of ammonia-oxidizers. These results underscore the significance of agricultural management practices in influencing the response of nitrogen cycling and the corresponding communities to drought.

How to cite: Bintarti, A. F., Kost, E., Kundel, D., Conz, R. F., Mäder, P., Krause, H.-M., Mayer, J., Hartmann, M., and Philippot, L.: Cropping system modulates the effect of drought on ammonia-oxidizing communities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18381, https://doi.org/10.5194/egusphere-egu24-18381, 2024.

The transition from dry-to-wet soils is often characterized by an acceleration of the nitrogen (N) cycle, representing a period of interest to biogeochemists studying future N cycling responses to global changes. In particular, wetting dry soils can produce large emission pulses of nitric oxide (NO; an air pollutant at high concentrations) and nitrous oxide (N₂O; a powerful greenhouse gas), but the mechanisms governing the N losses remain unresolved. The asynchronous timing of when N becomes bioavailable and when ecosystem N sinks activate (e.g., plant N uptake) post wetting has often been used to explain why N is lost when dry soils wet up. However, other factors directly affecting nitrifying communities may also contribute to the emissions. For instance, ammonia oxidizing bacteria (AOB) may be favored over ammonia oxidizing archaea (AOA) in NH₄⁺-rich environments that are typically observed in dry soils. Because AOB may process N less efficiently than AOA, shifts in nitrifier activity may help promote gaseous N losses.

To better understand mechanisms for gaseous N loss, we studied drylands in southern California that can experience >6 months without rain, as well as other drylands where we added or excluded precipitation during the dry summer or wet winter seasons. We also selectively inhibited AOA and AOB communities to measure their contributions to soil N emissions. Excluding precipitation during the winter prior to collecting soils did not affect NO emissions, but either adding or excluding precipitation during the summer did; NO emissions after adding extra rainfall (95 ± 6 µg NO g soil^-1; p = 0.01) or excluding rainfall (105 ± 22 µg NO g soil^-1; p = 0.006) were significantly higher than the control (41 ± 6 µg NO g soil^-1), with over 50% of the emissions controlled by AOB. While most of the effects of manipulating precipitation were observed on NO emissions, N₂O increased only when we excluded precipitation in the winter wet season, averaging 0.58 ± 0.40 µg N-N₂O g soil^-1. Using isotopologues of N₂O coupled with chloroform fumigations to slow microbial activity, we found that N retention and loss trade off as dry conditions intensify. Altogether, our measurements suggest that that shifts in precipitation patterns can favor AOB-derived NO emissions when dry soils are wetted at the end of the dry season, suggesting that shifts in nitrifier activity from the legacies of past precipitation can also help explain why N is lost when dry soils are wetted.

How to cite: Homyak, P.: Soil nitrogen cycling in dry lands: Precipitation legacy effects on microbial N loss pathways, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4788, https://doi.org/10.5194/egusphere-egu24-4788, 2024.