Terrestrial ecosystems are being exposed to warming and to more frequent and intense drought and rainfall events as a result of climate change. Such changes can have strong implications for biogeochemical cycling and the functioning of soils. Understanding the mechanisms that control the responses to environmental stress is critical for improving predictions on the resistance and resilience of terrestrial ecosystems on a changing world.
The aim of this session is to bridge the knowledge of different disciplines to elucidate the processes and feedbacks underpinning the biogeochemical response to climate change, with emphasis on warming, drought, and drying-rewetting events. This session will give a broad overview of empirical and modelling studies across different scales, considering how climate change affects terrestrial biogeochemistry and the interactions between soil microorganisms, plants and fauna. We will focus on the resilience and the associated recovery dynamics of soil biota to environmental disturbances, as well as on their resistance or adaptation mechanisms to climate change. We will bring together researchers from different environments and create a discussion platform to review the current state-of-the-art, identify knowledge gaps, share ideas, and tackle new challenges in the field.
vPICO presentations: Mon, 26 Apr
Model projections predict that climate change impacts on the tropics will include an increased frequency of drought and precipitation cycles. Such environmental fluctuations at the soil pore-scale play an important role in shaping microbial adaptive capacity, and trait composition of a community, which feeds back on to the breakdown and formation of soil organic matter (SOM). Understanding the factors controlling the carbon balance of humid tropical forest soils remains a social imperative. Microbial feedback to SOM pools is critical. Herein, we examine the microbial response to drought perturbations across 3 different, but complementary scales. At the largest scale, we explored the impacts of drought across a 1 m precipitation gradient spanning four 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 by 50 %. In addition, 4 corresponding control plots were also constructed. At the meso-scale, we incubated intact soil cores from one of these sites (P12) under 3 different hydrological treatments (control, drought, rewetting-drying cycles) for over a 5-month period. For the field and meso-scale experiments, we evaluated changes imparted by hydrological perturbations using multi-omic approaches, and physico-chemical measurements. In order to identify the traits involved in response to drought at the field and meso-scale, we isolated a range of bacteria to subject to stress at the scale of the single-cell and simple communities. Cell extracts were subjected to osmotic or matric stress and the short-term physiological responses determined using non-destructive synchrotron radiation-based Fourier Transform-Infrared spectromicroscopy. Through this approach, we identified changes in metabolic allocation within different cells, in particular to the secondary metabolome of the different bacteria. Our contribution will discuss the outcomes of these multi-scale experiments. Specifically focusing on how shifts in the microbial community and physiological changes may influence tropical soil carbon stability under future scenarios of altered drought and precipitation cycles.
How to cite: Chacon, S. S., Khurram, A., Bill, M., Bechtel, H., Voriskova, J., Chen, L., Dietterich, L. H., Karaoz, U., Holman, H.-Y., Cusack, D. F., and Bouskill, N.: Responses of Soil Microbes to Hydrological Perturbations in Tropical Forest Soils, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3786, https://doi.org/10.5194/egusphere-egu21-3786, 2021.
Climate change results in more frequent and intensified drought and rainfall events. The environment exerts a strong control on microbial communities, where drying and rewetting disturbances act as an additional stress that can alter soil processes driving the carbon cycle. Therefore, understanding the environmental control of microbial responses to drying and rewetting events is important to understand the microbial mechanisms controlling the soil C cycle. This study investigated how climate along with soil physiochemical factors affected microbial responses to drying and rewetting. A total of 40 soils across Europe presenting a comprehensive gradient from arctic (N Sweden) to southern Mediterranean (S Greece) climates and wide range of soil properties (SOM: 2-82%, pH: 3.9-7.4, Clay: 8-79%) were exposed to four days of drying followed by rewetting. The microbial growth and respiration responses after rewetting were monitored in high time resolution during 32h. The recovery time of bacterial growth to rates of 50% in undisturbed soil was used as a measure of how resilient microbial communities were to drying and rewetting.
The bacterial recovery time after rewetting ranged between 0.6-40h. We found that soils in arid climates had faster bacterial recovery times, suggesting that bacterial communities were more resilient and better adapted to drying and rewetting than those in humid climates, rendering microbial C-use during drying and rewetting more efficient. Furthermore, pH and soil organic matter also had pronounced effects on the resilience of bacterial growth, where acid pH and high soil organic matter resulted in bacterial communities that were slower to recover. In contrast, clay did not have an influence on the resilience of bacterial growth. Our findings suggest that both climate and soil properties are important when determine how soil microbial communities will respond to a drying and rewetting disturbance.
How to cite: Winterfeldt, S., Leizeaga, A., and Rousk, J.: Microbial responses to drying and rewetting in soils across a European climate transect, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11260, https://doi.org/10.5194/egusphere-egu21-11260, 2021.
In the mid-latitudes, climate change is characterized by a shift towards more persistent precipitation regimes, i.e. longer periods of both drought and precipitation. The effect of such a shift on a grass-legume grassland was simulated in a 480-day field mesocosm experiment. Treatments of the gradient design differed in the length of alternating dry/wet periods of 1, 3, 6, 10, 15, 20, 30, and 60 days, either starting with a dry or a wet period, resulting in 16 different treatments. All treatments received the same total amount of water, i.e., all dry periods were alternated with wet periods of equivalent duration and all treatments finished having received an even number of periods. Each mesocosm was planted with 12 common grassland species varying in traits (grasses/forbs/legumes).
Plant survival, diversity and aboveground biomass production were monitored regularly throughout the experiment. Microbial diversity was investigated after 60 and 120 days of experiment. Soil samples from the beginning and the end of the experiment were analyzed for root biomass, organic carbon, nitrogen, bulk density, soil water retention, pore size distribution, microbial biomass, basal respiration, nematodes, mesofauna and macrofauna. Hydrophobicity and infiltration was measured at the end of the experiment. We hypothesized that with more persistent weather, plant and soil biodiversity and functioning would become exponentially impaired and that this would occur at different tipping points for different ecosystem components.
Plant diversity decreased as expected with increased weather persistence, mostly due to loss of forbs and N-fixers, with a tipping point around a blocking duration of 20 days after the end of the first growing season (120 days). These initial diversity losses could be traced to the timing and intensity of the preceding dry periods. By the end of the experiment (480 days), species richness showed a more linear response pattern, suggesting disappearance of the initial timing & tipping point effects, yet this may in part be attributed to preclusion of non-native colonization throughout the experiment. Plant productivity first followed a similar but less steep decline, possibly because reduced water availability was partly compensated by greater nutrient supply rate observed after longer droughts. Later, productivity overall decreased especially in grasses and evened out possibly reflecting the cumulative nutrient depletion associated with previous harvests, nutrient leaching and/or microbial/plant immobilization or higher plant density. However, the negative response of the N-fixer/grass production ratio to weather persistence became even more pronounced.
After 120 days, microbial biomass was affected negatively by the 60-day treatment with a tendency of fungal biomass and F:B ratio to peak under intermediate weather persistence. Bacterial alpha diversity reacted negatively to persistent weather after 60 days within dry start treatments with tipping point around 10 days, but the trend was opposite after 120 days in both wet and dry treatments. Fungal beta diversity (community dissimilarity) was also positively influenced by more persistent weather.
Furthermore we found that with longer drought, studied soils became increasingly hydrophobic and this reduced initial infiltration rates. We discuss how this effect could exacerbate drought stress as well as increase erosion risk in sloping grasslands.
How to cite: Vindušková, O., Reynaert, S., Li, L., Zi, L., Donnelly, C., Lenaerts, B., Van Sundert, K., Vicena, J., Benetková, P., Deckmyn, G., Vancampenhout, K., Frouz, J., Vicca, S., De Boeck, H. J., Asard, H., Beemster, G. T. S., Laukens, K., Verbruggen, E., and Nijs, I.: Impact of more persistent precipitation regimes on a temperate grassland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13074, https://doi.org/10.5194/egusphere-egu21-13074, 2021.
In forest ecosystems, microorganisms hold key functions as nutrient cyclers, decomposers, plant symbionts or pathogens and thereby regulate biogeochemical processes and forest health. These microbial dynamics are controlled by water availability in three fundamental ways: as resource, as solvent, and as transport medium. For one of the dominant tree species in Swiss forests - Scots pine (Pinus sylvestris L.) - high mortality rates have been observed in recent decades. In the Rhone valley of Switzerland, forest dieback appears to be primarily caused by direct effects of drought and an increasing susceptibility of trees to further constraints, such as pathogen attacks. Nonetheless, water limitation does not affect soil microbes and trees separately but rather induces a series of interconnected effects between trees and the associated soil microbiome, which could strongly alter carbon and nutrient cycling in forests. We conduct a study to investigate the effects of drought on the biological interplay between Scots pine trees and soil microbial communities. We aim to estimate how shifts in microbial community composition and functional capacity under drought may affect nutrient cycling and tree vitality potentially contributing to tree mortality. In order to understand these mechanisms, we perform greenhouse experiments with tree-soil mesocosms under controlled conditions. State-of-the art molecular methods such as metabarcoding of ribosomal markers, shotgun metagenome sequencing, and qPCR of key functional genes are used to unravel alterations in the soil microbiome and in the underlying functional metabolic potential related to drought and associated tree-mortality. Furthermore, to elucidate the impact of drought on microbial carbon dynamics, stable isotope labelling techniques have been applied to trace 13C labeled plant photosynthates into the soil microbial communities by analyzing 13C signatures of phospholipid fatty acids. Investigation of soil physicochemical properties and tree-vitality is done in parallel with the microbial assessments to understand the feedbacks on nutrient-cycling and the soil-tree continuum. The overarching aim of this study is to gain new insights into the complex relationships between soil, trees and microbes under drought.
How to cite: Jäger, A., Hartmann, M., Hagedorn, F., Six, J., and Solly, E.: Investigating the drought-prone biological interplay of soil microbial communities and Scots pine trees, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16542, https://doi.org/10.5194/egusphere-egu21-16542, 2021.
The alternation of drought periods and rainfall events, intensified by climate change, has huge impacts on carbon cycle dynamics. Changes in soil moisture induce significant releases of CO2 from soils to the atmosphere. This phenomenon, known as the Birch effect, is accompanied by drastic changes in the microbiology as well. Based on the response patterns of microbial growth and respiration to the rewetting of dry soil, two different types have been identified. Microbial communities either respond immediately after rewetting and start increasing growth in a linear way (so-called “type 1” response), or they recover growth after a lag phase preceding an exponential increase (“type 2” response). The reasons behind the different responses, including how harsh the drought is perceived by the communities and what history of moisture conditions they were subjected to, are not yet fully resolved. Moreover, most studies focus on the top few centimeters of soil and the effect of depth and the contribution of deeper soils to the overall dynamics have been largely overlooked.
In order to investigate the influence of depth on microbial dynamics during drought and rainfall events, taking into account land-use, we performed a set of laboratory experiments that were also used to parameterize and validate numerical modelling-based analysis of the ecology driving soil biogeochemistry. We collected soil samples from permanent pasture and tilled and cropped arable fields at two different depths (0-5 cm and 20-30 cm). We then subjected them to a week of air drying followed by rewetting to optimal moisture, and measured respiration, bacterial growth and fungal growth at high temporal resolution.
The patterns were significantly different between soil types, showing type 1 responses in arable soils and type 2 responses in pasture soils. The type 1 responses in arable soils were also characterized by a higher carbon use efficiency after the rewetting perturbation. Moreover, the deeper microbial communities were relatively more affected by the drying and rewetting experiment than the respective shallow ones. Taken together, these results suggested that the drying and rewetting event was perceived by soil microbial communities as a stronger disturbance in the pasture soils, and at deeper depths, as illustrated by more sensitive microbial responses.
We then incorporated these laboratory data into a soil microbial model (EcoSMMARTS) and identified the depth- and community-specific differences in osmolyte regulation, necromass turnover, and cell residue activity as the microbial mechanisms potentially explaining the observed patterns. These findings provide insights into soil-climate feedback from different ecosystems, where intensively used arable soils were more resilient than permanent pasture soils and stored larger amounts of carbon due to a higher fraction of microbial growth to respiration under climate change scenarios. The capacity of microbial communities to adapt and regulate soil carbon dynamics is not uniform through the soil profile nor across management practices, therefore indicating a need for future studies incorporating depth and especially land-use which has the strongest effect on microbial activity during soil drying and rewetting.
How to cite: Lyonnard, B., Brangarí, A., and Rousk, J.: The interactive effect of land-use and soil depth on microbial activity during drying and rewetting – an experimental and computational investigation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15232, https://doi.org/10.5194/egusphere-egu21-15232, 2021.
The frequency and severity of droughts are expected to increase in the wake of climate change. Drought events not only cause direct impacts on the ecosystem carbon balance but also result in legacy effects during the following years. These legacies result from, for example, drought damage to the xylem or the crown which causes impaired growth, or from higher vulnerability to pests and diseases. To understand how droughts might affect the carbon cycle in the future, it is important to consider both direct and legacy effects. Such effects likely affect interannual variability in C fluxes but are challenging to detect in observations, and poorly represented in models. Therefore, the patterns and mechanisms inducing the legacy effects of drought on ecosystem carbon balance are necessarily needed to improve.
In this study, we analyze gross primary productivity (GPP) from eddy-covariance measurements in Germany to detect legacy effects from recent droughts. We follow a data-driven modeling approach using a random forest model trained in different sets of drought and non-drought periods. This approach allows quantifying legacy effects as deviations of observed GPP from modeled GPP in legacy years, which indicates a change in the vegetation response to hydro-climatic conditions as compared with the training period.
How to cite: Yu, X., Orth, R., Reichstein, M., and Bastos, A.: Legacy effects of drought on gross primary productivity from eddy-covariance measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9522, https://doi.org/10.5194/egusphere-egu21-9522, 2021.
In summer 2018, Northern Europe experienced an extreme summer drought in combination with unusually high temperatures, which had a substantial impact on agricultural yields as well as on forest growth conditions in various ways. An earlier study, using ICOS RI (Integrated Carbon Observation Research Infrastructure) stations and other forest ecosystem stations in the Nordic region, shows that the drought dramatically decreased NEP in the southern Scandinavian and Baltic region, almost nullifying the carbon sinks in some of the forests . Such severe conditions during a single year could be expected to influence a forest over following several years. Reduced tree storage of carbohydrates leads to a changed carbon allocation pattern in spring that may affect both the woody growth and pests' resistance. It is thus important to reveal the impact of such climatic events over a more extended period.
This study aims at assessing the carry-over effects of the extreme weather conditions on the carbon and water fluxes and the forest growth to the years after the event. The analysis is based on measurement from the stations shown to be significantly affected by the drought through reduced carbon fluxes in 2018: the spruce forests Hyltemossa and Skogaryd and the mixed forests Norunda, Svartberget, Soontaga and Rumperöd. The ecosystem carbon and water fluxes will, together with tree-ring width data, be used to assess the carbon and water exchange and growth recovery in the years after the extreme 2018 drought (2019 and 2020) by comparisons to earlier normal years and extreme events.
 Lindroth, A., et al. (2020): Effects of drought and meteorological forcing on carbon and water fluxes in Nordic forests during the dry summer of 2018 Phil. Trans. R. Soc. B37520190516 https://doi.org/10.1098/rstb.2019.0516
How to cite: Linderson, M.-L., Holst, J., Edvardsson, J., Heliasz, M., Klemedtsson, L., Klosterhalfen, A., Krasnova, A., Linderson, H., Martínez García, E., Mölder, M., Peichl, M., Sohar, K., Soosaar, K., Tung Chen, T., Vestin, P., Weslien, P., and Lindroth, A.: Boreal forest carbon exchange and growth recovery after the summer 2018 drought, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10253, https://doi.org/10.5194/egusphere-egu21-10253, 2021.
Tropical forests, while only occupying 12% to 15% of the Earth's surface, contain about 25% of the world's carbon biomass, with soils representing the second largest reservoir. Yet, recent studies have suggested that, in response to changing environmental conditions, in future decades tropical forests can switch from carbon sinks to carbon sources, with profound implications for the global carbon cycle. Most of these conclusions result from studies in lowland humid forests. However, other tropical forests, such as those occurring in the Andes are also important determinants of regional-to-global biogeochemical functioning, and their sensitivity to future warming has been less studied than in lowland forests. In this study, we explore intra and interspecific thermal sensitivity of soil respiration and its components (autotrophic and heterotrophic) in 15 dominant tree species in the tropical Andes, through an experimental thermosecuence in the Colombian Andes that uses elevation as a proxy for warming. In this thermosequence, a common garden experiment was set up and individuals from 15 dominant species were planted in three sites that represent a temperature gradient: the higher elevation site (2452 masl) corresponds to the base condition; the mid-elevation site (1326 masl) represents a warming of 8°C; and the lower site (575 masl) and it represents a warming of 12°C. Our results indicate consistently higher respiration values with increased temperature both within and between tree species. We used 𝑸10 values (the factor by which soil respiration increases for every 10-degree rise in temperature) to determine the temperature sensitivity of soil respiration. More specifically, for a warming of 5°C there is a temperature coefficient of 𝑸10 = 2 and for a warming of 9°C and there is a temperature coefficient 𝑸10 = 3, this means that for the greater increase temperature the soil respiration can increase faster. Notably, our results show that not all species respond equally to augmented temperatures, highlighting the potential for differential effects of increased temperature and more generally, of environmental change in the compositions and function of these strategic ecosystems. Collectively, our results are relevant for the management and adaptation of ecosystems, particularly tropical Andean forest, and for the refinement of ecological models that support projections of global environmental change and carbon cycle.
How to cite: Ocampo Montoya, E., Nottingham, A. T., Villegas Palacio, J. C., Mercado, L. M., Restrepo, Z., and Meir, P.: Warming effects on soil CO2 efflux in the tropical Andes: Insights from an experimental thermosequence with dominant tree species., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13864, https://doi.org/10.5194/egusphere-egu21-13864, 2021.
Plant litter chemistry is altered during decomposition but it remains unknown if these alterations, and thus the composition of residual litter, will change in response to climate. Selective microbial mineralization of litter components and the accumulation of microbial necromass can drive litter compositional change, but the extent to which these mechanisms respond to climate remains poorly understood. We addressed this knowledge gap by studying needle litter decomposition along a boreal forest climate transect. Specifically, we investigated how the composition and/or metabolism of the decomposer community varies with climate, and if that variation is associated with distinct modifications of litter chemistry during decomposition. We analyzed the composition of microbial phospholipid fatty acids (PLFAs) in the litter layer and measured natural abundance δ13CPLFA values as an integrated measure of microbial metabolisms. Changes in litter chemistry and δ13C values were measured in litterbag experiments conducted at each transect site. A warmer climate was associated with higher litter nitrogen concentrations as well as altered microbial community structure (lower fungi:bacteria ratios) and microbial metabolism (higher δ13CPLFA). Litter in warmer transect regions accumulated less aliphatic‐C (lipids, waxes) and retained more O‐alkyl‐C (carbohydrates), consistent with enhanced 13C‐enrichment in residual litter, than in colder regions. These results suggest that chemical changes during litter decomposition will change with climate, driven primarily by indirect climate effects (e.g., greater nitrogen availability and decreased fungi:bacteria ratios) rather than direct temperature effects. A positive correlation between microbial biomass δ13C values and 13C‐enrichment during decomposition suggests that change in litter chemistry is driven more by distinct microbial necromass inputs than differences in the selective removal of litter components. Our study highlights the role that microbial inputs during early litter decomposition can play in shaping surface litter contribution to soil organic matter as it responds to climate warming effects such as greater nitrogen availability.
How to cite: Kohl, L., Myers-Pigg, A., Edwards, K. A., Billings, S. A., Warren, J., Podrebarac, F. A., and Ziegler, S. A.: Microbial inputs at the litter layer translate climate into altered organic matter properties, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5218, https://doi.org/10.5194/egusphere-egu21-5218, 2021.
Seasonality of soil microorganisms plays a critical role in terrestrial carbon (C) and nitrogen (N) cycling. The asynchrony of immobilization by microbes and uptake by plants may be important for N retention during winter, when plants are inactive. Meanwhile, the known warming effects on soil microbes (decreasing biomass and increasing growth rates) may affect microbial seasonal dynamics and nutrient retention during winter.
We sampled soils from a geothermal warming site in Iceland (www.forhot.is) which includes three in situ warming levels (ambient, +3 °C, +6 °C). We harvested soil samples at 9 time points over one year and measured the seasonal variation in microbial biomass carbon (Cmic) and nitrogen (Nmic) and microbial physiology (growth and carbon use efficiency) by an 18O-labelling technique.
We observed that Cmic and Nmic peaked in winter, followed by a decline in spring and summer. In contrast growth and respiration rates were higher in summer than winter. The observed biomass peak at lower growth rates, suggests that microbial death rates must have declined even more than growth rates. Soil warming increased biomass-specific microbial activity (i.e., growth, respiration, and turnover rates per unit of microbial biomass), prolonging the period of higher microbial activity found in summer into autumn and winter. Microbial carbon use efficiency was unaltered by soil warming. Throughout the seasons, warming reduced Cmic and Nmic, albeit with a stronger effect in winter than summer and restrained winter biomass accumulation by up to 78% compared to ambient conditions. We estimated a reduced microbial winter N storage capacity by 45.5 and 94.6 kg ha-1 at +3 °C and +6 °C warming respectively compared to ambient conditions. This reduction represents 1.57% and 3.26% of total soil N stocks, that could potentially be lost per year from these soils.
Our results clearly demonstrate that soil warming strongly decreases microbial C and N immobilization when plants are inactive, potentially leading to higher losses of C and N from warmed soils over winter. These results have important implications as increased N losses may restrict increased plant growth in a future climate.
How to cite: Gündler, P., Canarini, A., Marañón Jiménez, S., Gunnarsdóttir, G., Sigurðsson, P., Peñuelas, J., Janssens, I. A., Sigurdsson, B. D., and Richter, A.: Warming affects seasonal dynamics of microorganisms and reduces the N storage capacity of soil microbes in winter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13232, https://doi.org/10.5194/egusphere-egu21-13232, 2021.
Temperature is one of the most important environmental factors controlling both microbial growth and respiration. Warmer temperatures accelerate the rate at which microorganisms respire. Therefore, it is expected that climate warming will induce losses of carbon to the atmosphere through soil microbial respiration, representing a positive feedback to climate warming. However, there are multiple gaps in our understanding on responses of microorganisms to warming. For instance, long-term experiments have shown that the increase in soil respiration found in warming experiments diminishes with time, recovering to ambient values. This suggests that soil C losses might not be as extensive as previously suggested. This can be due to substrate depletion or shifts in the microbial community composition that led to thermal adaptation. To test thermal adaptation of soil microbial communities to their climate, variation along latitudinal gradients is a useful context. Such geographical gradients have long-term and large temperature differences thus patterns in thermal adaptation should have had sufficient time for ecological and evolutionary processes to act, allowing us to test if soil microbial communities have adapted to thermal regimes.
We investigated a latitudinal gradient across Europe with 76 sites that spanned a gradient of decadal mean annual temperature (MAT) from -3.1 to 18.3°C. We investigated if respiration, bacterial and fungal growth responses were adapted to long-term temperature differences in this gradient. We did this by estimating the temperature dependences of bacterial growth, fungal growth and respiration. We determined the temperature sensitivity (Q10), the minimum temperature (Tmin) for growth and the optimum temperature (Topt) for growth. These metrics were then correlated to MAT. Additionally, we sequenced bacterial (16S) and fungal (ITS) amplicons from the different sites to also assess variance in community composition and structure. We hypothesized that microbes should be adapted to their historical temperature; microbial communities in warmer environments will be warm-shifted and vice versa.
We could effectively represent temperature relationships for bacterial growth, fungal growth, and respiration for all soils. As expected, temperature relationships correlated with the environmental temperature of the site, such that higher temperatures resulted in microbial communities with warm-adapted growth and respiration. This could be seen as a strong positive correlation between Tmin values and environmental temperatures which range from -14 to -5°C for bacteria, -11.5 to -4°C for fungi and -8 to -2°C for respiration. We found that MAT explains the microbial communities’ temperature dependencies for bacterial growth and respiration, but not for fungal growth. With 1°C rise in MAT, Tmin increased 0.17°C for bacterial growth, while Tmin for respiration increased by 0.11. Similarly, bacterial and fungal communities’ composition were correlated with MAT (r2=0.38; r2=0.62), and Tmin (r2=0.16; r2=0.21). These findings suggest that thermal adaptation occurs in processes such as bacterial growth and respiration, probably due to shifts in the microbial community composition. However, fungal growth seems to be less sensitive to changes in temperature, even though fungal communities’ composition was correlated with MAT.
How to cite: Cruz Paredes, C., Tajmel, D., and Rousk, J.: Microbial temperature adaptation across a European gradient, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4867, https://doi.org/10.5194/egusphere-egu21-4867, 2021.
In temperate soil systems microbial biomass often increases during winter and decreases again in spring. This build up and release of microbial carbon could potentially lead to a build-up of stabilized soil carbon during winter times. The mechanism behind the increase in microbial carbon is not well understood. In this laboratory incubation study, we looked into microbial physiology as well as microbial glucose uptake and partitioning during cooling. Soils from a temperate forest and agricultural system were cooled down from field temperature of 11°C to 1°C. We added 13C-labelled glucose immediately and after an acclimation phase of 7 days and traced the 13C into microbial biomass, CO2 respired from the soil and phospholipid fatty acids. In addition we determined microbial growth using 18O-incorporation into DNA.
First results show that while total respiration was strongly reduced when soils were cooled, glucose-derived respiration was as high in soils at 1°C as at 11°C. The same general pattern was found in soils during fast cooling and after an acclimation phase in agricultural and forest soils. We also saw an increased investment of glucose-derived carbon in unsaturated PLFAs. Since unsaturated fatty acids retain fluidity at lower temperatures compared to saturated fatty acids, this could be interpreted as precaution to reduced temperatures and potential freezing.
Our results show a distinct response of the soil microbial community to cooling. The maintained glucose-derived respiration and incorporation into PLFAs at low temperatures compared to field temperature might indicate a preferential use of labile C forms during cooling. Moreover, the 13C incorporation into PLFAs may signal the buildup of cooling resistant cell membranes. These findings will be discussed with results from the 13C label tracing into microbial biomass, extractable organic carbon and total soil carbon as well as data on microbial growth and carbon use efficiency.
How to cite: Schnecker, J., Spiegel, F., Fuchslueger, L., Li, Y., and Richter, A.: Microbial response to cooling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7732, https://doi.org/10.5194/egusphere-egu21-7732, 2021.
Soil temperatures are rising in the Arctic and will likely increase soil microbial activity. The magnitude of subsequent carbon effluxes is difficult to predict but is critical for evaluating the strength of the soil carbon-climate feedback as climate change intensifies. Soil respiration in the Arctic has a relatively high sensitivity to temperature increases. This is hypothesized to be a consequence of physiological adaptation of soil microbial communities to low temperatures. A variety of experimental and gradient studies have suggested that the growth-temperature relationship of bacterial communities will adapt to soil warming. It remains an open question whether this is driven by changes in community structure. In order to test this hypothesis, we collected 8 soils from the sub- to High Arctic and exposed them to a 0-30 ⁰C temperature gradient. We determined the temperature relationships and community composition of the resulting bacterial communities. To account for substrate depletion we sampled both after 100 days, as well as after a standardized amount of respiration. Temperature relationships were computed by fitting a square root model to leucine incorporation rates measured from 0-40 ⁰C. We will show the relationship between legacy effects of the soil thermal regime and the degree of temperature adaption and discuss whether the soil bacterial community structure is likely to influence soil respiration in Arctic soils under future climate conditions.
How to cite: Rijkers, R., Rousk, J., Aerts, R., and Weedon, J. T.: Will the temperature sensitivity of Arctic soil bacterial communities alter under warmed soil conditions?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5539, https://doi.org/10.5194/egusphere-egu21-5539, 2021.
Studying the diversity and abundance of cryoconite biota is relevant due to global climate warming, since organo-mineral particles in their composition have a significant impact on the ice albedo decrease and, thus, increase the rate of glacier melting. Since cryoconites are "hot spots" for biota development and the only loci where soil-like bodies can form on glaciers, they contribute significantly to the cycles of biogenic elements of ice and oligotrophic ecosystems.
Samples were collected from cryoconites from the Garabashi (GBg_c) and Shkhelda (SHKg_c) glaciers as well as from moraine (Garabashi); nearby soils (Chernozem, Forest-meadow, and organo-accumulative soil) were used as controls.
GBg_c samples were characterized by potentially higher values of microbial biomass (abundance of 16 S rRNA gene copies and ITS), with maximal values in samples taken from the cracked glacier. In contrast, minimal abundance values of the studied taxonomic markers in SHKg_c were determined. The values for the samples of nearby soils occupied an intermediate position. These results may be partially explained by different colors of cryoconites, determined by differences in their biochemical composition and origin: the GBg_c were represented by "black dust", with low values of albedo and, accordingly, higher values of temperature and moisture, apparently, more favorable for microbial activity compared to the "gray" dust of the SHKg_c.
Taxonomic structure analysis revealed a specific pattern of GBg_c samples– an oligotrophic psychrophilic community with a pronounced cyanobacterial dominance was detected. Despite significant differences between cryoconites and nearby moraine in the presence of major autotrophic representatives (cyanobacteria Tychonema, Phormidesmis), the heterotrophic component is similar and is represented by a very specific set of soil microorganisms of Bacteroides, Shingomonas, Burkholderiales groups, apparently, due to the flushing out of part of the microbiome from the autotrophic microbial consortia of the glacier, explaining, as well, the grouping of these samples in the Bray-Curtis NMDS ordination. No autotrophic microbiota predominance was detected in SHKg_c, these microbiomes were typical for soils without vegetative cover, as well as without biofilms on the surface (Verrucromicrobia, Sphingomonacia, Bacteroides). A low number of phylotypes was detected for the community of the GBg_c and Сhernozem. Moreover, the alpha-diversity indices were inversely proportional to the results of microbial biomass estimation, which can be explained by greater "homogeneity" (and, apparently, narrower functional specialization) of more numerous communities.
The metabolic profile of cryoconites (according to Picrust2) is characterized by the predominance of aerobic metabolic enzymes (cytochrome c) and proteins (amino acid synthesis), indicating a potentially high level of metabolic activity of the cryoconite microbial community. These results can be explained by the reparative needs of microbial cells under the conditions of oxygenic stress and extremely low temperatures. In contrast to the control soils (especially, Chernozem), relatively low levels of the catalytic pathway and carbon exchange were determined for the cryoconites’ metabolic pathways, possibly associated with both low available carbon stocks and supply of the glacier surface, as compared to soils with higher stocks of available forms of mineral nutrition.
The work is supported by RFBR project No 19-05-50107.
How to cite: Ivanova, E., Gladkov, G., Kimeklis, A., Kichko, A., Andronov, E., Zverev, A., Tembotov, R., and Abakumov, E.: The structure and diversity of microbiomes of glacial cryoconites (North Caucasus Region), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8275, https://doi.org/10.5194/egusphere-egu21-8275, 2021.
Soil microbial communities perform vital ecosystem functions, such as the decomposition of organic matter to provide plant nutrition. However, despite the functional importance of soil microorganisms, attribution of ecosystem function to particular constituents of the microbial community has been impeded by a lack of information linking microbial function to community composition and structure. Here, we propose a function-first framework to predict how microbial communities influence ecosystem functions.
We first view the microbial community associated with a specific function as a whole, and describe the dependence of microbial functions on environmental factors (e.g. the intrinsic temperature dependence of bacterial growth rates). This step defines the aggregate functional response curve of the community. Second, the contribution of the whole community to ecosystem function can be predicted, by combining the functional response curve with current environmental conditions. Functional response curves can then be linked with taxonomic data in order to identify sets of “biomarker” taxa that signal how microbial communities regulate ecosystem functions. Ultimately, such indicator taxa may be used as a diagnostic tool, enabling predictions of ecosystem function from community composition.
In this presentation, we provide three examples to illustrate the proposed framework, whereby the dependence of bacterial growth on environmental factors, including temperature, pH and salinity, is defined as the functional response curve used to interlink soil bacterial community structure and function. Applying this framework will make it possible to predict ecosystem functions directly from microbial community composition.
How to cite: Rousk, J. and Hicks, L.: Towards a function-first framework to make soil microbial ecology predictive, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14139, https://doi.org/10.5194/egusphere-egu21-14139, 2021.
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