SSS4.8

EDI
Aboveground-belowground feedbacks under climate change: linking process understanding to ecosystem-response prediction

Ecosystem responses to climate change depend on both long-term and dynamic feedbacks occurring between soils, plants and microbial communities. Soil resources and microbial nutrient mineralization mediate vegetation growth. In turn, plants control soil properties through the production of organic residues which are decomposed in the soil, the supply of photosynthates to the rhizosphere, as well as the association with belowground communities. The interactive effects of these responses in the context of changing environmental conditions have a key influence on soil biogeochemistry and the belowground storage of carbon. In this session we invite contributions from manipulative field experiments, observations in natural-climate gradients, and modelling studies that explore the impact of climate change on plant-growth dynamics, microbial diversity and metabolism, as well as soil biogeochemical cycling. Submissions that adopt novel approaches (e.g. molecular, isotopic) or synthesize large-scale outputs focusing on plant-soil-microbe feedbacks to warmer temperatures or water limitation are also highly welcome.

Public information:
Abstract EGU21-13734 will not be presented
Co-organized by BG1
Convener: Emily SollyECSECS | Co-conveners: Paul Hanson, Michael W. I. Schmidt, Jennifer SoongECSECS, Erik Verbruggen
vPICO presentations
| Mon, 26 Apr, 09:00–10:30 (CEST)
Public information:
Abstract EGU21-13734 will not be presented

Session assets

Session materials

vPICO presentations: Mon, 26 Apr

Chairpersons: Emily Solly, Erik Verbruggen, Michael W. I. Schmidt
09:00–09:05
Responses to changes in light availability
09:05–09:15
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EGU21-12657
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ECS
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solicited
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Highlight
Lena Neuenkamp, Martin Zobel, Kadri Koorem, Teele Jairus, John Davison, Maarja Öpik, Martti Vasar, and Mari Moora

Woody plant encroachment is influencing many open, grassy ecosystems across the globe, such as savanna, tundra and temperate grassland ecosystems. Drivers of woody plant encroachment are local land use change and global climate change, with shifts in grazing and mowing regimes as important local drivers and elevated CO2 levels, higher temperature and altered precipitation amounts as global drivers. Encroachment of woody species into open, herbaceous ecosystems comes along with substantial shifts in soil conditions, a reduction light availability and ultimately vegetation shifts in the understorey towards species better adapted to the ambient conditions. While vegetation shifts in response to woody plant encroachment in grassy ecosystems have been frequently investigated, e.g. regarding altered plant composition and functional traits related to resource acquisition and dispersal, consequences for biotic interactions have been less studied.

The symbiosis of plant roots with mycorrhizal fungi is one of the most relevant biotic interaction for plants species, with over 90% of all plants forming mycorrhizal symbiosis and arbuscular mycorrhizal symbiosis as the most prominent mycorrhizal type among herbaceous species. Plants involved in the arbuscular mycorrhizal (AM) symbiosis trade photosynthetically derived carbon for fungal-provided soil nutrients. However, little is known about how plant light demand and ambient light conditions influence root-associating AM fungal communities, and thus their response to prominent climate change processes like shrub encroachment.

We conducted a manipulative field experiment to test whether plants’ shade tolerance influences their root AM fungal communities in open and shaded grassland sites. We found that light-dependent shifts in AM fungal community structure were similar for experimental bait plant roots and the surrounding soil. Yet, lower AM fungal beta and gamma diversity for shade-intolerant plants in shade likely reflected preferential carbon allocation to specific AM fungi due to the limited plant carbon available to support symbiotic fungi. We conclude that favourable environmental conditions, including optimal light availability, widen the plant biotic niche, i.e. selectivity for specific AM fungi is reduced, and compatibility with a larger number of AM fungal taxa is promoted. With respect to predicted stronger woody plant encroachment predicted under current climate change scenarios, these results indicate that we might be losing AM fungal diversity and the functions associated with these fungal taxa. This calls for continous investment into conservation efforts and management practices to counteract this trend and keep savanna, tundra and grassland ecosystems open. 

How to cite: Neuenkamp, L., Zobel, M., Koorem, K., Jairus, T., Davison, J., Öpik, M., Vasar, M., and Moora, M.: Light availability and light demand of plants shape the arbuscular mycorrhizal fungal communities in their roots , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12657, https://doi.org/10.5194/egusphere-egu21-12657, 2021.

Responses to warming
09:15–09:17
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EGU21-11056
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ECS
Zuonan Cao, Zhenhuan Guan, Peter Kühn, Jinsheng He, and Thomas Scholten

Many species showed that their richness and distribution shifts climate-driven towards higher elevation in Tibetan Plateau. However, vegetation and soil data from alpine grassland elevational gradients are rare (Huang et al., 2018). It is mostly unknown how the "grass-line" will respond to global warming and whether soils play a significant role in the vegetation pattern in high-altitude regions. At a local scale, the growth and distribution of vegetation at its upper limit may depend on nutrient limitation, as shown for treelines from the Himalayas. For example, the limited nutrient supply of soil N, K, Mg, and P becomes more intense with elevation, which declines in nutrient supply spatially coincides with abrupt changes in vegetation composition and growth parameters (Schwab et al., 2016). And low soil nutrient availability could affect tree growth in the Rolwaling Himal, Nepal treeline ecotone (Drollinger et al., 2017). To better understand the interrelationship between soil properties and grass growth at this upper limit, we took random soil samples in 3 altitudes, 3 geomorphic positions with 3 depth increments from Haibei grassland, northern Tibetan Plateau. Soil properties, like texture, bulk density, total C, N, and P fractions, were analyzed and compared to vegetation data.
Further, soil and vegetation data from open-top chambers (OTC) experiments to simulate global warming were analyzed better to understand the role of temperature for grass line-shift. The first results show that species composition change with altitude towards grassland plant communities with lower demands for P, which can be compared with the nutrient addition experiment that P addition alone significantly affects species diversity and biomass in the same area (Ren et al., 2016). We suppose that specific combinations of soil properties could limit grass growth and be even more marked than the warming, which controls biodiversity and biomass production in high mountain grassland ecosystems. 

How to cite: Cao, Z., Guan, Z., Kühn, P., He, J., and Scholten, T.: Do soil properties with elevation affect alpine "grass-line"? Findings from Haibei, northern Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11056, https://doi.org/10.5194/egusphere-egu21-11056, 2021.

09:17–09:19
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EGU21-16305
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ECS
Sylvain Monteux and the co-authors

Considering the potential positive feedback between climate warming and the release of greenhouse gases following the increased decomposition of the organic matter stored in permafrost soils as they thaw is an important challenge for the upcoming climate change assessments. While our understanding of physico-chemical constraints on thawing permafrost SOM decomposition has vastly improved since IPCC’s fifth assessment report, biotic interactions can still be the source of large uncertainties. Here we discuss the effects of two biotic interactions in the context of thawing permafrost: rhizosphere priming effect and microbial functional limitations. Rhizosphere priming effects are still-unclear mechanisms that result in increased SOM decomposition rates in the vicinity of plant roots. We consider these effects through the PrimeSCale modeling framework, discussing its predictions and its limitations, in particular which observations and data should be acquired to further improve it. Microbial functional limitations were recently evidenced in permafrost microbial communities and consist in missing or impaired functions, likely due to strong environmental filtering over millennial time-scales. We present what this mechanism can imply in terms of permafrost soil functioning and briefly discuss what could be the next steps before its inclusions in modeling efforts.

How to cite: Monteux, S. and the co-authors: Microbial functional limitations and rhizosphere priming effect in permafrost, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16305, https://doi.org/10.5194/egusphere-egu21-16305, 2021.

09:19–09:21
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EGU21-1118
Ofiti O.E. Nicholas, Zosso U. Cyrill, Solly F. Emily, Hanson J. Paul, Wiesenberg L.B. Guido, and Schmidt W.I. Michael

More than one third of global soil organic matter (SOM) is stored in peatlands, despite them occupying less than 3% of the land surface. Increasing global temperatures have the potential to stimulate the decomposition of carbon stored in peatlands, contributing to the release of disproportionate amounts of greenhouse gases to the atmosphere but increasing atmospheric CO2 concentrations may stimulate photosynthesis and return C into ecosystems.  Key questions remain about the magnitude and rate of these interacting and opposite processes to environmental change drivers.

We assessed the impact of a 0–9°C temperature gradient of deep peat warming (4 years of warming; 0-200 cm depth) in ambient or elevated CO2 (2 years of +500 ppm CO2 addition) on the quantity and quality of SOM at the climate change manipulation experiment SPRUCE (Spruce and Peatland Responses Under Changing Environments) in Minnesota USA. We assessed how warming and elevated CO2 affect the degradation of plant and microbial residues as well as the incorporation of these compounds into SOM. Specifically, we combined the analyses of free extractable n-alkanes and fatty acids together with measurements of compound-specific stable carbon isotopes (δ13C).

We observed a 6‰ offset in δ13C between bulk SOM and n-alkanes, which were uniformly depleted in δ13C when compared to bulk organic matter. Such an offset between SOM and n-alkanes is common due to biosynthetic isotope fractionation processes and confirms previous findings. After 4 years of deep peat warming, and 2 years of elevated CO2 addition a strong depth-specific response became visible with changes in SOM quantity and quality. In the upper 0-30 cm depth, individual n-alkanes and fatty acid concentrations declined with increasing temperatures with warming treatments, but not below 50 cm depth. In turn, the δ13C values of bulk organic matter and of individual n-alkanes and fatty acids increased in the upper 0-30 cm with increasing temperatures, but not below 50 cm depth. Thus n-alkanes, which typically turnover slower than bulk SOM, underwent a rapid transformation after a relatively short period of simulated warming in the acrotelm. Our results suggest that warming accelerated microbial decomposition of plant-derived lipids, leaving behind more degraded organic matter. The non-uniform, and depth dependent warming response implies that warming will have cascading effects on SOM decomposition in the acrotelm in peatlands. It remains to be seen how fast the catotelm will respond to rising temperatures and atmospheric CO2 concentrations.

How to cite: Nicholas, O. O. E., Cyrill, Z. U., Emily, S. F., Paul, H. J., Guido, W. L. B., and Michael, S. W. I.: Warming and elevated CO2 promote incorporation of plant-derived lipids into soil organic matter in a spruce-dominated ombrotrophic bog, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1118, https://doi.org/10.5194/egusphere-egu21-1118, 2021.

09:21–09:23
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EGU21-13734
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ECS
Tatjana Živković, Alyssa A Carell, Gustaf Granath, Mats B Nilsson, Manuel Helbig, Denis Warshan, Ingeborg Jenneken Klarenberg, Daniel Gilbert, A. Jonathan Shaw, Joel E Kostka, and David J Weston

Peatlands store about third of the terrestrial carbon (C) and exert long-term climate cooling. Dominant plant genera in acidic peatlands, Sphagnum mosses, are main contributors to net primary productivity. Through associative relationships with diverse microbial organisms (microbiome), Sphagnum mosses control major biogeochemical processes, namely uptake, storage and potential release of carbon and nitrogen. Climate warming is expected to negatively impact C accumulation in peatlands and alter nutrient cycling, however Sphagnum-dominated peatland resilience to climate warming may depend on Sphagnum-microbiome associations. The ability of the microbiome to rapidly acclimatize to warming may aid Sphagnum exposed to elevated temperatures through host-microbiome acquired thermotolerance. We investigated the role of the microbiome on Sphagnum’s ability to acclimate to elevated temperatures using a microbiome-transfer approach to test: a) whether the thermal origin of the microbiome influences acclimation of Sphagnum growth and b) if microbial benefits to Sphagnum growth depend on donor Sphagnum species.

            Using a full-factorial design, microbiomes were separated from Sphagnum “donor” species from four different peatlands across a wide range of thermal environments (11.4-27°C). The microbiomes were transferred onto germ-free “recipient” Sphagnum species in the laboratory and exposed to a range of experimental temperatures (8.5 – 26.5°C) for growth analysis over 4 weeks.

            Normalized growth rates were maximized for plants that received a microbiome from a matched “donor” and with a similar origin temperature (ΔTtreatment-origin: 0.3±0.9°C [±standard error], p = 0.73). For non-matched “donor-recipient” Sphagnum pairs, ΔTtreatment-origin was slightly negative with -4.1±2.1°C (p = 0.06). The largest growth rate of the “recipient” was measured when grown with a microbiome from a matching “donor” Sphagnum species and was 252% and 48% larger than the maximum growth rate of the germ-free Sphagnum and the non-matched “donor-recipient” Sphagnum pairs, respectively.

            Our results suggest that the composition of the Sphagnum microbiome plays a critical role in host plant temperature acclimation. We found that microbially-provided benefits to the host plant were most pronounced when: 1) the thermal origin of the microbiome is similar to experimental temperatures, and 2) when donor and recipient Sphagnum species are the same. Together, these results suggest that Sphagnum temperature acclimation can be modulated, in part, by microbial interactions and may potentially play a role in peatland resilience to climate warming.

How to cite: Živković, T., Carell, A. A., Granath, G., Nilsson, M. B., Helbig, M., Warshan, D., Klarenberg, I. J., Gilbert, D., Shaw, A. J., Kostka, J. E., and Weston, D. J.: Microbial community composition is linked to Sphagnum acclimation to warming, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13734, https://doi.org/10.5194/egusphere-egu21-13734, 2021.

09:23–09:25
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EGU21-16406
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ECS
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Highlight
Effects of temperature rise (+5°C) on millet growth and mycorrhization and soil microbial community of culture
Sally Diatta, Hassna Mboup-Founoune, Sidy Diakhaté, and Diégane Diouf
09:25–09:27
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EGU21-4921
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ECS
Cyrill Zosso, Nicholas O.E. Ofiti, Jennifer L. Soong, Emily F. Solly, Margaret S. Torn, Arnaud Huguet, Guido L.B. Wiesenberg, and Michael W.I. Schmidt

Soils will warm in near synchrony with the air over the whole profiles following global climate change. It is largely unknown how subsoil (below 30 cm) microbial communities will respond to this warming and how plant-derived soil organic carbon (SOC) will be affected. Predictions how climate change will affect the large subsoil carbon pool (>50 % of SOC is below 30 cm soil depth) remain uncertain.

At Blodgett forest (California, USA) a field warming experiment was set up in 2013 warming whole soil profiles to 100 cm soil depth by +4°C compared to control plots. We took samples in 2018, after 4.5 years of continuous warming and investigated how warming has affected the abundance and community structure of microoganisms (using phospholipid fatty acids, PLFAs), and plant litter (using cutin and suberin).

The warmed subsoil (below 30 cm) contained significantly less microbial biomass (28%) compared to control plots, whereas the topsoil remained unchanged. Additionally below 50 cm, the microbial community was different in warmed as compared to control plots. Actinobacteria were relatively more abundant and Gram+ bacteria adapted their cell-membrane structure to warming. The decrease in microbial abundance might be related to lower SOC concentrations in warmed compared to control subsoils. In contrast to smaller SOC concentrations and less fine root mass in the warmed plots, the concentrations of the plant polymers suberin and cutin did not change. Overall our results demonstrate that already four seasons of simulated whole-soil warming caused distinct depth-specific responses of soil biogeochemistry: warming altered the subsoil microbial community, but not concentrations of plant-derived soil organic carbon.

How to cite: Zosso, C., Ofiti, N. O. E., Soong, J. L., Solly, E. F., Torn, M. S., Huguet, A., Wiesenberg, G. L. B., and Schmidt, M. W. I.: Whole-soil warming alters microbial community, but not concentrations of plant-derived soil organic carbon in subsoil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4921, https://doi.org/10.5194/egusphere-egu21-4921, 2021.

09:27–09:29
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EGU21-4801
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ECS
Adetunji Alex Adekanmbi, Laurence Dale, Liz Shaw, and Tom Sizmur

Predicting the pattern of soil organic matter (SOM) decomposition as a feedback to climate change, via release of CO2, is extremely complex and has received much attention. However, investigations often do not differentiate between the extracellular and intracellular processes involved and work is needed to identify their relative temperature sensitivities. Samples were collected from a grassland soil at Sonning, UK with average daily maximum and minimum soil temperature of 15 °C and 5 °C. We measured potential activities of β-glucosidase (BG) and chitinase (NAG) (extracellular enzymes) and glucose-induced CO2 respiration (intracellular enzymes) at a range of assay temperatures (5 °C, 15 °C, 26 °C, 37  °C, and 45 °C). The temperature coefficient Q10 (the increase in enzyme activity that occurs after a 10 °C increase in soil temperature) was calculated to assess the temperature sensitivity of intracellular and extracellular enzymes activities. Between 5 °C and 15 °C intracellular and extracellular enzyme activities had equal temperature sensitivity, but between 15 °C and 26°C intracellular enzyme activity was more temperature sensitive than extracellular enzyme activity and between 26 °C and 37 °C extracellular enzyme activity was more temperature sensitive than intracellular enzyme activity. This result implies that extracellular depolymerisation of higher molecular weight organic compounds is more sensitive to temperature changes at higher temperatures (e.g. changes to daily maximum summer temperature) but the intracellular respiration of the generated monomers is more sensitive to temperature changes at moderate temperatures (e.g. changes to daily mean summer temperature). We therefore conclude that the extracellular and intracellular steps of SOM mineralisation are not equally sensitive to changes in soil temperature. The finding is important because we have observed greater increases in average daily minimum temperatures than average daily mean or maximum temperatures due to increased cloud cover and sulphate aerosol emission. Accounting for this asymmetrical global warming may reduce the importance of extracellular depolymerisation and increase the importance of intracellular catalytic activities as the rate limiting step of SOM decomposition.

How to cite: Adekanmbi, A. A., Dale, L., Shaw, L., and Sizmur, T.: Temperature Sensitivity of Intracellular and Extracellular Soil Enzyme Activities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4801, https://doi.org/10.5194/egusphere-egu21-4801, 2021.

Responses to drought
09:29–09:31
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EGU21-3380
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ECS
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Highlight
Claudia Guidi, Ivano Brunner, Josephine Imboden, Konstantin Gavazov, Marcus Schaub, and Frank Hagedorn

European forests are facing higher frequencies of extreme droughts, potentially impairing tree growth and ecosystem functioning. Drought limits the metabolic activity of plants and soil organisms, either directly or through reduced belowground carbon (C) allocation of recent assimilates, thus affecting C cycling in the plant-soil system. However, the net effect on belowground soil C storage is still unclear, as drought suppresses both C inputs from plants and outputs from soils. Moreover, understanding the underlying mechanisms is complicated due to long-term acclimation and adaptation of plant and soil organisms to water limitation.

We investigated the impact of repeated summer droughts in a Scots pine (Pinus sylvestris L.) forest on soil C storage and C cycling, taking advantage of a large-scale irrigation experiment  running since 2003 in a dry inner-Alpine valley in Switzerland (Pfynwald, Valais), which removed the “natural” water limitation. We assessed the responses of soil organic carbon (SOC) stocks and C fluxes by measuring litter fall and decomposition, fine root biomass and production, soil CO2 effluxes, C-mineralization, and 13C-labelled glucose utilization by soil microorganisms. 

After 16 years of irrigation, the organic layers lost significant amounts of C (-1000 g m-2), despite a 50% increase in litter fall. This C loss was almost compensated by a C gain in the mineral soil (+870 g m-2) under irrigation. The decrease in C storage in the organic layers can be related to a three-fold increase in litter decomposition mainly through soil macrofauna as indicated by a litter-bag experiment. In parallel, the C gain in the mineral soil can be attributed mainly to increased incorporation of litter by soil fauna, together with greater C input from the rhizosphere (+70% fine root biomass for Scots pine in mineral soil). Furthermore, irrigation stimulated soil CO2 efflux as well as microbial C-mineralization of organic and mineral soil, indicating enhanced soil C cycling. Addition of 13C-enriched glucose to mineral soils revealed a stronger utilization of this easily available C substrate in the drought than in the irrigated soils, together with a negative priming of soil organic matter (SOM) decomposition shortly after substrate addition. These results suggest that the altered quantity and quality of C inputs under irrigation has increased the availability of easily degradable C in soil.

This study reveals that long-term summer irrigation in a drought-prone pine forest has strong impacts on multiple interlinked processes of the soil C cycle. The removal of water limitation strongly altered vertical soil C distribution, accelerated soil C cycling and altered the substrate use by soil organisms, but had only a small net effect on the whole-profile SOC stocks.

How to cite: Guidi, C., Brunner, I., Imboden, J., Gavazov, K., Schaub, M., and Hagedorn, F.: Long-term irrigation in a drought-prone pine forest leads to vertical redistribution of C stocks and accelerates C cycling in the soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3380, https://doi.org/10.5194/egusphere-egu21-3380, 2021.

09:31–09:33
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EGU21-8870
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ECS
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Highlight
Natalie Oram, Johannes Ingrisch, Gerd Gleixner, Nadine Praeg, Paul Illmer, Fiona Brennan, Richard Bardgett, and Michael Bahn

Plant and soil communities are intimately connected. Plants shape soil microbial community composition through their resource acquisition strategies and via root carbon (C) inputs, which has cascading effects on biogeochemical cycles. Drought has been shown to disrupt the connection between plants and soil microorganisms. However, the effects of drought intensity on soil microbial community functioning, including the uptake of recent plant-derived C, are largely unknown. Here, we determined how two plant communities with contrasting resource acquisition strategies (acquisitive versus conservative) responded to a gradient of drought (control, and eight drought intensities). Using a 13C pulse labelling approach, we tracked C allocated from plants to soil and its uptake by the microbial community. We measured potential extracellular enzyme activity as a proxy of microbial community functioning. We hypothesized that (1) drought responses are non-linear, and (2) acquisitive plant communities have lower drought resistance but recover faster than conservative plant communities, which is reflected in lower 13C transfer and reduced microbial functioning during drought and increases after drought. In general, we found that the responses we measured were non-linearly related to drought intensity. After three weeks of drought, drought intensity decreased aboveground net primary productivity (ANPP) of both plant communities. Soil extractable organic 13C decreased with increasing drought intensity, indicating that less recently assimilated C was allocated to root exudation. Although microbial biomass remained stable over the drought intensity gradient, 13C uptake into microbial biomass decreased at peak drought, and was lower in the conservative vs. acquisitive plant community at mild drought levels. Potential enzyme activity of β-1,4-glucosidase, involved in cellulose breakdown, and  β-N-acetyl-glucosaminidase, involved in chitin breakdown, decreased with increasing drought intensity. Urease activity was higher in conservative than acquisitive plant communities exposed to drought. Seven days after re-wetting, we found that microbial uptake of 13C increased along the drought gradient and was higher than the control in communities previously subjected to high drought intensities. This fast microbial recovery could affect nutrient mobilisation, which could underlie longer-term plant community recovery. Two months after re-wetting, we indeed found that plant communities that had previously experienced high drought intensity (> 75% soil water deficit) had higher ANPP than the control. We conclude that drought intensity has significant non-linear effects on microbial uptake of recent plant C and on potential extracellular enzyme activities both during drought and recovery, with consequences for plant community recovery dynamics.  

How to cite: Oram, N., Ingrisch, J., Gleixner, G., Praeg, N., Illmer, P., Brennan, F., Bardgett, R., and Bahn, M.: Drought intensity effects on grassland plant communities and soil microbial community function, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8870, https://doi.org/10.5194/egusphere-egu21-8870, 2021.

09:33–09:35
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EGU21-6770
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ECS
Alberto Canarini, Lucia Fuchslueger, Jörg Schnecker, Margarete Watzka, Erich M. Pötsch, Andreas Schaumberger, Michael Bahn, and Andreas Richter

The raise of atmospheric CO2 concentrations, with consequent increase in global warming and the likelihood of severe droughts, is altering the terrestrial biogeochemical carbon (C) cycle, with potential feedback to climate change.  Microbial physiology, i.e. growth, turnover and carbon use efficiency, control soil carbon fluxes to the atmosphere. Thus, improving our ability to accurately quantify microbial physiology, and how it is affected by climate change, is essential. Recent advances in the field have allowed the quantification of community-level microbial growth and carbon use efficiency in dry conditions via an 18O water vapor equilibration technique, allowing for the first time to evaluate microbial growth rates under drought conditions.

We modified the water vapor equilibration method using 2H-labelled water to estimate microbial community growth via deuterium incorporation into fatty acids. First, we verified that a rapid equilibration of 2H with soil water is possible. Then, we applied this approach to soil samples collected from a long-term climate change experiment (https://www.climgrass.at/) where warming, elevated atmospheric CO2 (eCO2) and drought are manipulated in a full factorial combination. Samples were taken in the field during peak drought and one week after rewetting. We used a high-throughput method to extract phospho- and neutral- lipid fatty acids (PLFA and NLFA) and we measured 2H enrichment in these compounds via GC-IRMS.

Our results show that within 48 h, 2H in water vapor was in equilibrium with soil water and was detectable in microbial PLFA and NLFAs. We were able to quantify growth rates for different groups of microorganisms (Gram-positive, Gram-negative, Fungi and Actinobacteria) and calculate community level carbon use efficiency. We showed that a reduction of carbon use efficiency in the combined warming + eCO2 treatment was caused by a reduced growth of fungi and overall higher respiration rates. During drought, all groups showed a reduction in growth rates, albeit the reduction was stronger in bacteria than in fungi. Moreover, fungi accumulated high amounts of 2H into NLFAs, representing up to one third of the amount in PLFAs and indicating enhanced investment into storage compounds. This investment was still higher than in control plots two days after rewetting and returned to control levels within a week.

Our study demonstrates that climate change can have strong effects on microbial physiology, with group-specific responses to different climate change factors. Our approach has the benefit of using fatty acid biomarkers to improve resolution into community level growth responses to climate change. This allowed a quantification of group-specific growth rates and concomitantly a measurement of investment into reserve compounds.

How to cite: Canarini, A., Fuchslueger, L., Schnecker, J., Watzka, M., Pötsch, E. M., Schaumberger, A., Bahn, M., and Richter, A.: Deuterium stable isotope probing of fatty acids reveals climate change effects on soil microbial physiology., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6770, https://doi.org/10.5194/egusphere-egu21-6770, 2021.

Responses to management and land use under climate change
09:35–09:37
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EGU21-12134
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ECS
Brunon Malicki, Jenni Nordén, Carl-Fredrik Johannesson, and Håvard Kauserud

 

Climate change and management effects on taxonomic and functional diversity of soil communities

Authors: Brunon Malicki1, 2, Jenni Nordén1, Carl-Fredrik Johannesson 1,
Håvard Kauserud2

Affiliations:

  • 1) Norwegian Institute for Nature Research (NINA), Oslo, Norway
  • 2) University of Oslo, Department of bioscience

               Boreal forests are crucial to the terrestrial carbon (C) stocks of the world, containing even 50% of all forest C, up to 80% of which can be located within their soils. There its cycle is regulated by a complex net of interactions between the organisms inhabiting it and the abiotic environment. Both climate change as well as anthropogenic disturbances in the form of management activities, can cause a reduction in their carbon stocks. For this reason, it is important to understand how  community structure is affected by the ongoing climate change and various management activities in boreal forest soil. This kind of understanding is necessary for informed actions to mitigate the consequences of climate change.                The aim of the project ForBioFunCtion is to assess the changes in boreal forest soil communities, as well as soil C fluxes that result from the activities of the soil communities, as a response to management and climate change. In order to do this, a chrono sequence has been set up in Norwegian bilberry spruce forests, including: a clear-cut, thinned middle-aged managed, mature managed as well as a near natural forest stand. Within each site, open top chambers, outfitted with heaters, will be placed, in order to stimulate an increase in temperature. Moreover, increased precipitation will be simulated by fortnightly watering. Lastly, nitrogen fertilizer or biochar will be added to experimental units within the clear-cut, thinned, middle-aged and mature managed stands. Each year, soil cores and dead wood samples will be taken from each experimental unit, and the communities inhabiting them will be analyzed with the use of next-generation sequencing and modern bioinformatics, in order to determine both the species as well as functional group composition. Moreover, mesh bags containing both plant and fungal necromass will be used for assessing the rate of litter decomposition under the different experimental conditions. The project aims to broaden the understanding of the response of soil communities to both climate change and improper forest management. This in turn could hopefully allow for creating methods of safeguarding the processes they regulate, as well as their diversity.

 

How to cite: Malicki, B., Nordén, J., Johannesson, C.-F., and Kauserud, H.:  Climate change and management effects on taxonomic and functional diversity of soil communities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12134, https://doi.org/10.5194/egusphere-egu21-12134, 2021.

09:37–09:39
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EGU21-845
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ECS
Xuehui Feng, Jie Hu, Yuanhe Yang, and Leiyi Chen

Elucidating the mechanisms underlying the changes in microbial physiology under anthropogenic nitrogen (N) input is of fundamental importance for understanding the carbon-N interaction under global environmental change. Carbon use efficiency (CUE), the ratio of microbial growth to assimilation, represents a critical microbial metabolic parameter that controls the fate of soil C. Despite the recognized importance of mineral protection as a driver of soil C cycling in terrestrial ecosystems, little is known on how mineral-organic association will modulate the response of microbial CUE to increasing N availability. Here, by combining a 6-year N‐manipulation experiment and 18O isotope incubation, mineral analysis and a two-pool C decomposition model, we evaluate how N-induced modification in mineral protection affect the changes in microbial growth, respiration and CUE. Our results showed that microbial CUE increased under N enrichment due to the enhanced microbial growth and decreased respiration. Such changes in microbial physiology further led to a significant decrease in CO2-C release from the slow C pool under high N input. More importantly, the disruption in mineral-organic association induced by elevated root exudates is the foremost reason for the enhanced microbial growth and CUE under high N input. Taken together, these findings provide an empirical evidence for the linkage between soil mineral protection and microbial physiology, and highlight the need to consider the plant-mineralogy-microbial interactions in Earth system models to improve the prediction of soil C fate under global N deposition.

How to cite: Feng, X., Hu, J., Yang, Y., and Chen, L.: Increasing microbial carbon use efficiency with nitrogen addition resulting from plant-mineral interaction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-845, https://doi.org/10.5194/egusphere-egu21-845, 2021.

09:39–09:41
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EGU21-14052
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ECS
Lucie Hublova and Jan Frouz

Soils and forest soil in particular represent important pools of carbon (C). Here, we present a quantitative review of common garden experiments in which various tree species were planted alongside each other in European countries to answer following questions: Does soil sequester more C under broadleaf than under conifer trees? and How do the effects of tree species and litter quality on soil C sequestration change with soil development (i.e., maturity) and other soil properties? We found that the effects of broadleaf and coniferous trees on C sequestration differed with the stage of soil development. In mature soils, more C was stored under coniferous trees than under broadleaf trees. In soils in early stages of soil development, on post-mining spoil heaps, the opposite trend was found, i.e., more C was stored under broadleaf. C sequestration under broadleaf trees was highest in immature soils and in soils with high pH. C sequestration was negatively correlated with the litter C:N ratio in post-mining soils but not in other more mature soils. Similarly C sequestration was negatively correlated with the litter C:N  in alkaline soils and in soil with high clay content. These results suggest that C sequestration mechanisms differ in immature vs. mature soils such that C storage is greater under broadleaf trees in immature soils but is greater under coniferous trees in mature soils. The study was supported by LIFE17/IPE/CZ/000005 project

How to cite: Hublova, L. and Frouz, J.: Contrasting  effect of coniferous and broadleaf trees on soil carbon storage during reforestation of mature soils and afforestation of immature soils, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14052, https://doi.org/10.5194/egusphere-egu21-14052, 2021.

09:41–09:43
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EGU21-16543
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ECS
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Highlight
Ainara Leizeaga, Lettice Hicks, Albert Brangarí, Carla Cruz-Paredes, Menale Wondie, Hans Sanden, and Johannes Rousk

Climate change predicts an increase in temperature and an intensification of the hydrological cycles resulting in more extreme drought and rainfall events. When dry soils experience a rainfall event, there is a big CO2 release from soil to the atmosphere which is regulated by soil microorganisms. In the present study, we set out to investigate how drought and warming affects the soil microbial responses to drying and rewetting (DRW); and how those responses are affected by differences in land use. Previous work has shown that exposure DRW cycles in the laboratory and in the field can induce faster recovery (more ‘resilient’) of the microbial responses after a DRW cycle. In addition, a history of drought has been suggested to result in microbial communities with higher carbon use efficiency (CUE) during DRW in a wet heathland in Northern Europe and in semi-arid grasslands in Texas. We wanted to extend these observations to subtropical environments.

 

With the aim of simulating drought and warming, rain shelters and open top chambers (OTC) were installed in Northern Ethiopia in 2 contrasting land-uses (a degraded cropland and a pristine forest) for 1.5 years. Soils were then sampled and exposed to a DRW cycle in the laboratory. Microbial growth and respiration responses were followed with high temporal resolution over 3 weeks, as well as, changes in microbial community structure.  

 

Microbial functions universally showed a resilient response after a DRW cycle, with bacterial growth and fungal growth increasing immediately upon rewetting linked with the expected respiration response. The field treatments and land-use differences, therefore, did not have an effect on the resilience of soil microbial communities to DRW cycles. There were differences between the two main decomposer groups: fungi were more resilient than bacteria, as they showed a faster recovery rate. Microbial CUE upon rewetting responded differently in the different field treatments and land-uses. CUE was generally higher in croplands than in forests. Besides, while simulated drought reduced CUE, simulated drought increased CUE. These differences might be explained by either (i) the selection or more efficient microbial communities due to a higher exposure to DRW events or (ii) differences in resource availability (i.e. plant input).  

How to cite: Leizeaga, A., Hicks, L., Brangarí, A., Cruz-Paredes, C., Wondie, M., Sanden, H., and Rousk, J.: Effects of land use, short-term drought and warming on microbial responses to drying and rewetting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16543, https://doi.org/10.5194/egusphere-egu21-16543, 2021.

09:43–10:30