Land use intensification, particularly a shift from extensively to intensively managed agroecosystems is often seen as one of the main drivers of global biodiversity decline and is considered the main factor applying pressure on soil biodiversity. When confronted with future land use change, understanding the responses of soil biodiversity to different land use regimes is decisive for adequate land management. However, there is still substantial uncertainty about how consistently different taxonomic groups respond to land use intensification. Oftentimes, different taxa show divergent responses to more intense land use regimes, and the community composition is rarely correlated with land use intensity, which may suggest that the drivers of community composition may not be the same as drivers of diversity. The mechanisms that determine the response of different taxa to land use intensification may be regulated by changes in the plant community and abiotic environmental drivers. We systematically assessed and quantified through meta-analysis the effects of land use intensification on soil organisms in global agroecosystems and analyzed the dependence of these effects on abiotic factors such as soil properties (organic matter, pH, nutrient and water availability, texture) and climatic zone.

How to cite: Betancur-Corredor, B. and Russell, D.: Response of soil fauna to land use intensification in a global meta-analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10271, https://doi.org/10.5194/egusphere-egu23-10271, 2023.

Crop diversification has gained importance in Brazilian soybean (Glycine max L.) cropping systems, usually cultivated in soybean/2^nd season maize (Zea mays L.) successions. Brachiaria grass (Urochloa spp.), a forage highly grown in Brazilian livestock systems, can be a suitable option for the soybean systems diversification. Brachiarias are well adapted to tropical conditions, produce high amounts of above and belowground biomass, have high nutrient cycling capacity, and release exudates known as biological nitrification inhibitors (BNI). All these traits might increase soybean yield and nutrient use efficiency in the agroecosystem.

Brazilian cropping systems rely on plant growth-promoting bacteria (PGPB), like seed inoculation of soybean with the nitrogen-fixing bacteria Bradyrhizobium, alone or in combination with Azospirillum, to replace mineral N fertilizers.

In this study, we aimed to investigate the soil bacterial community (activity and diversity) response to the diversification of soybean/maize cropping systems with Urochloa ruziziensis and inoculation with different combinations of PGPB. We hypothesize that inoculation with PGPB and diversification of the system with maize intercropped with Brachiaria will enhance microbial community activity and diversity.

A 5-year experiment has been conducted in Londrina (Paraná State, Southern Brazil) in a randomized complete block design with a split-plot arrangement and six replicates. Main plots consisted of soybean during the cash crop season (S: soybean without inoculation; Si: soybean inoculated with Bradyrhizobium; Sc: soybean co-inoculated with Bradyrhizobium + Azospirillum). Sub-plots consisted of different diversification systems after the cash crop season (M: succession with maize; M+U: maize intercropped with U. ruziziensis; Mi+Ui: maize intercropped with U. ruziziensis, both inoculated with Azospirillum). After the soybean harvest in the 2021/2022 cropping season, soil samples were taken at the 0-10 cm soil layer. We analyzed soil enzymes (arylsulfatase, β-glucosidase, and acid phosphatase), environmental factors (soil pH and nutrients), and the 16S gene sequence.

Preliminary results suggest an increase in the relative abundance of some bacterial phyla with Brachiaria. The phylum Proteobacteria, which harbors numerous PGPB, showed higher relative abundance in the cropping systems with Brachiaria, independently of the inoculation strategy in the summer soybeans. On the other hand, for the Nitrospirota phylum, which contains nitrite-oxidizing bacteria, higher relative abundance was observed in S/MiBi and Si/MiBi, compared with Sc/MiBi. Additional results on bacterial community diversity and composition and their relationship with microbial activity and environmental indicators will be discussed.

This study provides novel insights into how crop diversification combined with PGPB affects the soil microbial community and nitrogen dynamics, supporting agricultural and soil management practices to achieve more sustainable production systems.

How to cite: Rewa Charnobay, A. C., Lalonde-Haman, C., Ferraz Helene, L. C., Gumiere, T., Hungria, M., and Nogueira, M. A.: Crop diversification and seed inoculation strategies effects on soil microbial community in soybean cropping systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-524, https://doi.org/10.5194/egusphere-egu23-524, 2023.

Soil bacterial communities play an important role in soil health, carbon (C), and nutrient cycling, as well as in soil-plant relationships in agroecosystems. However, our understanding of the drivers and distribution of soil bacterial communities across landscapes is limited. For example, it is not clear how changes in soil management practices (i.e. Till vs No-till vs cover crop), soil diagnostic units, and their associated physical-chemical properties interact to influence the composition and abundance of soil bacterial communities at a larger scale. Here, using samples collected in a countrywide soil survey in Hungary, we combined soil metagenomic sequencing, soil management practices, and soil geochemical data to develop a mechanistic understanding of the drivers of bacterial communities in contrasting agroecosystems. We found that bacterial community composition and distribution significantly differed between soil management practices. Furthermore, we found that soil geochemical properties influenced soil bacterial composition and abundance under similar soil diagnostic units, suggesting that the effects of soil management practices on bacterial communities outweighed the ones of pedogenic processes. Together, these results suggest that soil management practices influence soil geochemical properties that drive the composition and spatial distribution of soil bacterial communities. Consequently, effects and types of soil management should be taken into account when developing soil health indicators for agroecosystems.

How to cite: Bukombe, B., Csenki, S., Szlatenyi, D., Czako, I., and Láng, V.: Distribution and drivers of soil bacterial communities across different soil management practices and soil diagnostic units in agricultural ecosystems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13475, https://doi.org/10.5194/egusphere-egu23-13475, 2023.

Thermal adaptation of soil microbial respiration has the potential to greatly alter carbon cycle-climate feedbacks through acceleration or reduction of soil microbial respiration as the climate warms. However despite its importance, the relationship between warming and soil microbial activity remains poorly constrained. Part of this uncertainty stems from persistent methodological issues and difficulties isolating the interacting effects of changes in microbial community responses from changes in soil carbon availability. To address these challenges, we sampled nearly 50 soils from around New Zealand, including from a long-term geothermal gradient, with mean annual temperatures ranging from 11-35°C. For each of these soils we constructed temperature response curves of microbial respiration given unlimited substrate and estimated a temperature optima (T_opt) and inflection point (T_inf). We found that thermal adaptation of microbial respiration occurred at a rate of 0.29°C ± 0.04 1SE for T_opt and 0.27°C ± 0.05 1SE for T_inf per degree of warming, demonstrating that thermal adaptation is considerably offset from warming. These relatively small changes occurred despite large structural shifts in microbial community composition and diversity. We also quantitatively assessed how thermal adaptation may alter potential respiration rates under future warming scenarios by consolidating all of the temperature response curves. Depending on the specific mean and instantaneous soil temperatures, we found that thermal adaptation of microbial respiration could both limit and accelerate soil carbon losses. This work highlights the importance of considering the entire temperature response curve when making predictions about how thermal adaptation of soil microbial respiration will influence soil carbon losses.

How to cite: Alster, C., van de Laar, A., Goodrich, J., Arcus, V., Deslippe, J., Marshall, A., and Schipper, L.: Quantifying soil microbial thermal adaptation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4609, https://doi.org/10.5194/egusphere-egu23-4609, 2023.

High-latitude soils are particularly vulnerable to temperature-driven C losses and may contribute substantially to the increasing atmospheric CO₂ concentrations. The magnitude of their contribution is, however, uncertain, and largely dependent on the interactions between C and nitrogen (N) biogeochemical cycles, soil microbial activities and the feedbacks between plants and soil microbes. Warming may cause a particularly pronounced acceleration of soil N transformation in N-poor cold regions. The consequent alleviation of plant N limitations in cold ecosystems may increase plant productivity and C inputs to the soil, compensating the expected soil C loss, at least partially. Alternatively, warming may desynchronize or unbalance the intimate coupling between microbial N mineralization and vegetation N uptake, leading to potential soil N loss, but also higher soil C losses. We aimed to elucidate potential mechanisms of ecosystem N losses in subarctic grasslands by determining the effects of soil warming on the seasonal patterns of plant N acquisition and microbial net N immobilization. For this, we performed a seasonal isotope tracing experiment using a mix of ¹⁵N-labelled amino-acids along soil temperature gradients in geothermal systems in Iceland.

Soil microbial biomass acted as a temporal reservoir of N by increasing N immobilization particularly during unfavorable winter periods for vegetation, likely due to the alleviated microbial C limitation. However, soil warming exacerbated microbial C limitation and decreased the N storage capacity of soil microbes during snowmelt periods. As a result, a higher proportion of N remained in the extractable soil fraction susceptible to leaching losses.  , however, this increased plant N uptake did not compensate for the lower microbial biomass N storage, leading to ecosystem N losses. Our results highlight the relevant role of soil microbes to safely store and immobilize N when plants do not need it and to release N when plants require it. Warming can weaken this particularly important soil microbial function in cold regions, leading to substantial ecosystem N and fertility losses, which may also promote irreversible soil C losses in these ecosystems.

How to cite: Marañón Jiménez, S., Luo, X., Richter, A., Gündler, P., Fuchslueger, L., Sigurdsson, B. D., Janssens, I., and Peñuelas, J.: Warming may cause substantial nitrogen losses from subarctic grasslands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12303, https://doi.org/10.5194/egusphere-egu23-12303, 2023.

Arctic ecosystems are experiencing a strong and fast warming in the realms of climate change, and understanding the involved processes are important to predict impacts and feedbacks on their C cycling. Winter warming leads to frequent and reoccurring snow melts and as a consequence exposed bare ground. This leads to accelerated freeze-thaw cycles, since the snow cover that was insulating the soil below to temperature variations around a few degrees minus now can be exposed to much harsher freezes. We experimentally exposed soil crusts from Greenland to freezing-thawing cycles of different intensities and frequencies and measured the abundance of the three soil microbial groups bacteria, fungi and protists with help of microfluidic soil chips. The soil chips are brought into tight contact with the soil sample, and the microbial community colonizes their transparent pore spaces which enable us to image-based analysis of microbial abundance and interactions. We found that increased freezing frequency (daily versus bi-weekly) strikingly reduced bacterial populations, stronger than increased freezing intensity (-5°C vs -18°C). We also exposed the soil chips to live-freezing under the microscope to analyze direct effects of the approaching ice front on the microbial community. At intermediate freezing temperatures, dead-end pockets in the pore space remained liquid-filled and could act as refugia for the organisms. Fast approaching ice fronts caught fleeing organisms and in some cases led to detrimental outcomes, especially for protists. Disturbances in the trophic network differently affecting predators and pray may thus also contribute to changes in the bacterial carbon cycling.

How to cite: Hammer, E., Duljas, J., Klingenhammer, F., Zou, H., Elberling, B., and Andresen, L. C.: Effects of intensified freezing-thawing cycles on arctic soil microbiota investigated via soil chips, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16057, https://doi.org/10.5194/egusphere-egu23-16057, 2023.

Almost half of Earth’s terrestrial surface is covered by drylands, where limitation of water restricts vascular plant growth. In these ecosystems, a substantial part of primary production instead takes place directly at the soil surface, within complex microbial communities forming biological soil crusts (biocrusts) that include intricately bound soil particles. These communities, composed mainly of cyanobacteria, algae, fungi, and bryophytes, are fundamental actors for dryland biogeochemical cycles, as they fix atmospheric CO₂ and N₂ and constitute one of the primary, if not the only, sources of soil C and N. Due to the vast spatial extent of biocrusts, accounting for up to 70% of the living land cover in drylands, their importance for C and N cycling extend to the global scale, i.e. accounting for 7% of global net primary production of total terrestrial vegetation. However, warming temperatures and increasing soil dryness following climate change are estimated to have critical implications on these systems; recent studies show i.e. warming-induced reduction of biocrust cover and, thus, reduced CO₂ uptake.

Our aim is to contribute to this relatively new research field by providing insights into biocrust-soil-microorganism interactions under elevated temperatures and drought at the process-scale. This was realized in a phytotron incubation experiment of soil-biocrust mesocosms with experimental warming and drought, during which CO₂ uptake and heterotrophic respiration was monitored. Dual labelling pulses (¹³CO₂ and ¹⁵N₂) were applied to follow the fate of recently fixed ¹³C and ¹⁵N into both particulate and mineral-associated SOM pools via physical fractionation and into microbial biomass via PLFA. Further, hyperspectral VIS-NIR images of the surface were recorded to quantify and determine crust cover and composition.

The results revealed clear drought effects—not only in a distinct reduction in CO₂ fixation by the biocrusts, but also in the elemental distribution of soil C underneath; the effect extended down into underlying soil layers, where biocrust-derived C contents were reduced by half due to drought. The change in the translocation of biocrust-derived C into the underlying soil was reflected in the ¹³C-PLFA profiles, showing how mainly fungi transform recently fixed C from the biocrust into their biomass in the biocrust layer, extending down into the underlying soil via fungal hyphae expansion. While drought clearly restricted the microbial abundance, warming further induced a microbial community shift, where a greater relative fungal dominance was determined under experimental warming—a shift, however, that was not reflected under dry conditions. A further combined effect was determined in N fixation, where we confirm a decrease in biocrust-derived N under drought under warming.

Our results showcase the implications of elevated temperature and drought on C and N fixation and cycling—the two most fundamental ecosystem functions in biocrust-soil systems. The results support the growing body of evidence of major implications for biogeochemical cycles in drylands in a warming world.

How to cite: Witzgall, K., Hesse, B. D., Grams, T. E. E., Pietrasiak, N., Seguel, O., Oses, R., Jansa, J., Guigue, J., Rojas, C., Rousk, K., and Mueller, C. W.: Soil carbon and nitrogen cycling at the atmosphere-soil interface: quantifying the response of biocrust-soil interactions to climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12299, https://doi.org/10.5194/egusphere-egu23-12299, 2023.

Tropical forest soils represent some of Earth's largest stores of soil carbon. Humid and warm conditions promote high primary productivity offsetting high ecosystem respiration rates, and this balance has resulted in significant carbon accumulation in plant biomass and soils. These vast carbon stocks can be destabilized under a changing climate, and model projections predict tropical and subtropical regions will experience disturbance to the hydrological cycle, with an increased likelihood of more frequent and prolonged droughts interspersed with periods of intense precipitation. Herein, we examine the functional response of belowground communities to a reduction in throughfall across a 1 m precipitation gradient (2350 to 3400 mm) spanning three sites from the Caribbean coast to the interior of Panama. At each site, 4 throughfall exclusion plots (10 x 10 m) were established to reduce precipitation, and exacerbate the natural variability in seasonal hydrological cycles. In January 2020, approximately 18 months since the inception of throughfall exclusion, each plot was sampled at six locations and two depths (0-10 and 10-20 cm). To identify the traits and mechanisms involved in responding to drought perturbation, we sequenced the microbiomes of the soil samples from the throughfall exclusion and corresponding controls at each site, and measured metabolite accumulation within the soils. Here we report on the accumulation of distinct metabolites along the precipitation gradient and under throughfall exclusion. We note that constitutive production of compatible solutes increases from the wettest to the driest site, indicative of trait selection due to climate history. However, under throughfall exclusion the gradient end members show a more muted metabolic response than the intermediate site. We discuss these responses with respect specific pathways invoked under drying stress, and soil carbon dynamics.  

How to cite: Chacon, S. S., Karaoz, U., Louie, K., Bowen, B., Northen, T., Dietterich, L. H., Cusack, D. F., and Bouskill, N.: Microbial metabolic response to throughfall exclusion and feedback on soil carbon dynamics along a tropical forest precipitation gradient, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9543, https://doi.org/10.5194/egusphere-egu23-9543, 2023.

The last decades were characterized by rising temperatures, enhanced atmospheric CO₂ concentrations, and by an increasing frequency of extreme events such as drought. Soil microorganisms are major drivers of biogeochemical processes, yet the effects of climate change in shaping microbial communities remain poorly understood.

To address this knowledge gap, we examined how future climate conditions (combined +300 ppm CO₂ and +3 °C warming, relative to ambient) and drought, alone and in combination, affect microbial community composition throughout the vegetation period in a sub-montane managed grassland (‘ClimGrass’ experiment; Styria, Austria). We combined amplicon sequencing of bacteria, archaea, and fungi with droplet digital PCR to perform quantitative microbiome profiling of seasonal and drought-legacy effects on soil microbial communities.

Drought strongly shaped the bacterial/archaeal and the fungal community structure during peak drought conditions, and this effect could still be detected two and fourteen months after ending drought by rewetting and removing rain-out shelters. In comparison, future climate conditions were observed to exert less pressure on the structure of bacterial/archaeal and fungal communities. Interestingly, abundances of members of Actinobacteria and Bacteroidota for bacteria, as well as Cladosporiaceae and Phaeosphaeriacea for fungi (amongst others) significantly increased during peak drought. Our findings suggest that drought can have immediate and lasting effects on the soil microbial community structure by contributing to the establishment of drought-tolerant microbial communities.

How to cite: Schmidt, H., Séneca, J., Canarini, A., Simon, E., Dietrich, M., Prommer, J., Bogdanovic, I., Martin, V., Mohrlok, M., Hausmann, B., Pötsch, E., Schaumberger, A., Wanek, W., Bahn, M., and Richter, A.: Drought legacy effects on microbial community structure in a managed grassland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14006, https://doi.org/10.5194/egusphere-egu23-14006, 2023.

Ecosystem restoration is known to enhance the functioning and stability of plant communities in the face of climate extremes. However, the effects of ecosystem restoration on soil microbial communities and their functional stability remain poorly understood. Here, we used a long-term (33 years) multiple factorial grassland restoration experiment to assess how different restoration approaches, including farmyard manure (FYM) addition, low amounts of inorganic fertiliser, mixed seed addition, and promotion of red clover, affect multiple dimensions of soil microbial functional stability in response to drought. We found that specific restoration approaches (e.g., FYM addition) not only increased the stability of plant biomass production, but also enhanced drought resistance of soil microbial multifunctionality. Moreover, we identified key factors that drive the multi-dimensional stability of plant and soil microbial communities, which provide mechanistic insights into how grassland restoration impacts above- and below-ground stability in the face of drought.

How to cite: Liu, S., Bilton, A., and Bardgett, R.: Restoration of soil microbial functional stability in the face of climate extremes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15955, https://doi.org/10.5194/egusphere-egu23-15955, 2023.