Displays

Microbial physiology may be critical for projecting future changes in soil carbon. Still, predicting the ecosystem implications of microbial processes remains a challenge. We argue that this challenge can be met by identifying microbial life history strategies based on their phenotypic characteristics, or traits, and representing these strategies in models simulating different environmental conditions. By adapting several theories from macroecology, we define microbial high yield (Y), resource acquisition (A), and stress tolerance (S) strategies. Using multi-omics and carbon stable isotope probing tools, we empirically validated our Y-A-S framework by studying variations in community traits along gradients of resource availability and abiotic conditions arising from anthropogenic change. Across a Britain-wide land use intensity gradient, we used isotope tracing and metaproteomics to show that microbial resource acquisition and stress tolerance traits trade off with growth yield measured as carbon use efficiency. Reduced community growth yield with intensification was linked to decreased microbial biomass and increased biomass-specific respiration which subsequently translated into lower organic carbon storage in such soil systems. We concluded that less-intensive management practices have more potential for carbon storage through increased microbial growth yield by greater channelling of substrates into biomass synthesis. In Californian grass and shrub ecosystems, we used metatranscriptomics and metabolomics to infer traits of in situ microbial communities on plant leaf litter in response to long-term drought. This experimental set-up provided gradients of resource availability and water stress. We observed that drought causes greater microbial allocation to stress tolerance. The most discernable physiological adaptations to drought in litter communities were production or uptake of compatible solutes like trehalose and ectoine as well as inorganic ions to maintain cellular osmotic balance. Grass communities also increased expression of genes for synthesis of capsular and extracellular polymeric substances possibly as a mechanism to retain water. These results showed a clear functional response to drought in grass litter communities with greater allocation to survival relative to growth that reduced decomposition under drought. In contrast, communities on chemically complex shrub litter had smaller differences in gene expression and metabolite profiles in response to drought, suggesting that the drought stress response is constrained by litter chemistry which also reduces decomposition rates. Overall, our findings suggest trade-offs between drought stress tolerance, resource acquisition and growth yield in communities across different ecosystems. These empirical studies demonstrate how trade-offs in key microbial traits can have consequences on soil carbon decomposition and storage. We recommend the use of our Y-A-S framework in experimental and modelling studies to mechanistically link microbial communities to system-level processes.

How to cite: Malik, A., Griffiths, R., and Allison, S.: Linking microbial communities to soil carbon cycling under anthropogenic change using a trait-based framework, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8424, https://doi.org/10.5194/egusphere-egu2020-8424, 2020.

Drought is a common stressor for soil organisms. One adaptive mechanism is “stress priming”, the ability to cope with a severe stress (“triggering”) by retaining a memory from a previous mild stress event (“priming”). While plants have been extensively investigated for drought memory, only scare information is available for filamentous soil fungi and its implications for soil microbial communities. We investigated the potential for drought-induced stress priming on single species as well its effect on microbial communities in forest A-horizons. Batch experiments with 4 treatments were conducted: exposure to priming and/or triggering as well as non-stressed controls. A priming stress was caused by desiccation to pF 4. The samples were then rewetted and after a recovery time of up to 14 days triggered (pF 6). After triggering, microbial biomass and activity as well as microbial communities by rDNA sequencing were analysed.

Some filamentous fungi show the potential for drought-induced stress priming leading to increased survival rates and activity under severe stress events. Yet, the effect seems to be species specific with potentially high impact on composition and activity of microbial communities considering the expected increase of drought events. Especially receptive to stress priming seem to be species within the fungal classes Mortierellomycetes, Pezizomycetes, and Tremellomycetes. Shifts in the microbial community compositions could be observed in some cases in response to stress priming. In general, the nature of the response depends on the original composition of the microbial community and the occurrence of a subsequent triggering event. For example, species investing high amounts of resources into the primed state only prevail if a triggering occurs (especially noteworthy was Byssonectria fusispora).

How to cite: Guhr, A.: Drought stress memory in filamentous soil fungi, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8695, https://doi.org/10.5194/egusphere-egu2020-8695, 2020.

The Paris climate agreement is pursuing efforts to limit the increase in global temperature to below 2 °C above pre-industrial level. The overall consequence of relatively slight warming (~2 °C), on soil C and N stocks will be dependent on microorganisms decomposing organic matter through release of extracellular enzymes. Therefore, the capacity of soil microbial community to buffer climate warming in long-term and the self-regulatory mechanisms mediating soil C and N cycling through enzyme activity and microbial growth require a detailed comparative study. Here, microbial growth and the dynamics of enzyme activity (involved in C and N cycling) in response to 8 years warming (ambient, +1.6 °C, +3.2 °C) were investigated to identify shifts in soil and microbial functioning. A slight temperature increase (+1.6 °C) only altered microbial properties, but had no effect on either hydrolytic enzyme activity or basic soil properties. Stronger warming (+3.2 °C) increased the specific growth rate (μ_m) of the microbial community, indicating an alteration in their ecological strategy, i.e. a shift towards fast-growing microorganisms and accelerated microbial turnover. Warming strongly changed microbial physiological state, as indicated by a 1.4-fold increase in the fraction of growing microorganisms (GMB) and 2 times decrease in lag-time with warming. This reduced total microbial biomass but increased specific enzyme activity to be ready to decompose increased rhizodeposition, as supported by the higher potential activitiy (V_max) and lower affinity to substrates (higher K_m) of enzymes hydrolyzing cellobiose and proteins cleavage in warmed soil. In other words, stronger warming magnitude (+3.2 °C) changed microbial communities, and was sufficient to benefit fast-growing microbial populations with enzyme functions that specific to degrade labile SOM. Combining with 48 literature observations, we confirmed that the slight magnitude of temperature increase (< 2 °C) only altered microbial properties, but further temperature increases (2-4 °C) was sufficient to change almost all soil, microbial, and enzyme properties and related processes. As a consequence, the revealed microbial regulatory mechanism of stability of soil C storage is strongly depended on the magnitude of future climate warming.

How to cite: Zhou, J., Wen, Y., Shi, L., Dippold, M., Kuzyakov, Y., Zang, H., Jones, D., and Blagodatskaya, E.: The magnitude of temperature increase matters: how will soil organic mineralization respond to future climate warming?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-269, https://doi.org/10.5194/egusphere-egu2020-269, 2020.

Despite the intensified efforts to understand the impacts of climate change on forest soil C dynamics, few studies have addressed the long term effects of warming on microbially mediated soil C and nutrient processes. In the few long-term soil warming experiments the initial stimulation of soil C cycling diminished with time, due to thermal acclimation of the microbial community or due to depletion of labile soil C as the major substrate for heterotrophic soil microbes. Thermal acclimation can arise as a consequence of prolonged warming and is defined as the direct organism response to elevated temperature across annual to decadal time-scales which manifest as a physiological change of the soil microbial community. This mechanism is clearly different from apparent thermal acclimation, where the attenuated response of soil microbial processes to warming is due to the exhaustion of the labile soil C pool.

The Achenkirch experiment, situated in the Northern Limestone Alps, Austria (47°34’ 50’’ N; 11°38’ 21’’ E; 910 m a.s.l.) is a long term (>15 yrs) soil warming experiment that has provided key insights into the effects of global warming on the forest soil C cycle. At the Achenkirch site, we have observed a sustained positive response of heterotrophic soil respiration and of soil CO₂ efflux to warming after nine years (2013), making it an appropriate setting for testing hypotheses about continued or decreasing warming effects at decadal scales. We collected soil from six warmed and six control plots in October 2019, from 0-10 cm and 10-20 cm depth, and incubated them at three different temperatures: ambient, +4, and +10 °C. We measured potential soil enzyme activities with fluorimetric assays, gross rates of protein depolymerization, N mineralization, and nitrification with ¹⁵N isotope pool dilution approaches, and microbial growth, respiration, and C use efficiency (CUE) based on the ¹⁸O incorporation in DNA and gas analysis.  Our preliminary results show that potential enzyme activities of aminopeptidase, N-acetylglucosaminidase, b-glucosidase, and acid phosphatase were stimulated by decadal soil warming by 1.7- to 3.5-fold, measured at the same i.e. ambient temperature. In contrast, the temperature sensitivity (Q10) remained unaltered between warmed and control soils for all enzyme activities (Q10=1.63-2.28), except for aminopeptidase where we observed a decrease in Q10 by 25% in warmed topsoils (0-10 cm). Aminopeptidase also had the highest temperature-sensitivity (Q10=2.39), causing a decrease of the enzymatic C: N acquisition ratio with warming. These results indicate an increasing investment in microbial N acquisition with warming. We will follow these trends based on results on gross rates of soil C and N processes, allowing to delineate decadal soil warming effects on soil microbial biogeochemistry and to understand their effect on the cross-talk between organic C and N cycling in calcareous forest soils.

How to cite: Urbina Malo, C., Tian, Y., Shi, C., Zhang, S., Heitger, M., Kwatcho, S., Borken, W., Heinzle, J., Schindlbacher, A., and Wanek, W.: Effect of forest soil warming on the rate and temperature sensitivity of microbial C and N processes in a temperate mountain forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11631, https://doi.org/10.5194/egusphere-egu2020-11631, 2020.

The summer of 2018 brought a record-breaking heat wave and record low rainfall, resulting in a severe drought in much of northern and central Europe. In the following year, precipitation increased but in many locations remained below average. A temporal study that began in 2017 in a temperate evergreen forest in the Netherlands allowed the opportunity examine the effects of this drought on functional traits before, during, and after the event. This gave us new trait-based insight into the resistance, resilience, and recovery abilities of the Douglas Fir to drought. During the growing season of 2017-2019, leaves were collected every 2-4 weeks. Functional traits were derived, including total chlorophyll, carotenoids, specific leaf area, and leaf dry matter content. Functional diversity metrics were also derived to examine response to drought. Using ANOVA to compare trait values during the same parts of the season, we found all traits showed significant changes at some point, but chlorophyll and carotenoids had the largest responses to the drought. Chlorophyll concentrations showed a continued decrease into 2019. Carotenoid concentration increased across the years, which has been shown to be an indication of plant stress. Though Douglas Fir has been considered drought resistant, this study reveals that the intensity of the 2018 drought had an impact on its traits and its resilience without sufficient soil moisture relief in the following year. Much attention has been paid to extreme events with climate change; however, it is these events paired with a lack of adequate recovery conditions that can push ecosystems past their tipping point.

How to cite: March, R., Paardekooper, M., Timmermans, J., Huisman, C., van der Aa, M., Chen, Q., Corbin, A., and van Bodegom, P.: The effect of drought on functional traits and diversity in Douglas Fir: snapshots before, during, and after the summer 2018 European drought event, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21256, https://doi.org/10.5194/egusphere-egu2020-21256, 2020.

Soil moisture and temperature collectively regulate the production and consumption of carbon in soils. With expected changes in both the soil thermal and hydrological regimes globally, experimental data on carbon turnover under these changes in contrasting ecosystems are important for constraining predictive models of soil carbon turnover. We investigated the effect of changes in soil water and temperature on heterotrophic respiration (Rh) and net methane uptake (MU) in soils from grassland ecosystems in Arctic, temperate and subtropical climates.
The temperature sensitivity of RH increased with decreasing mean annual temperature, but there was no indication of a site-specific response of Rh to changes in soil moisture. All sites displayed MU, primarily controlled by the soil water content with little temperature dependence. Thus, the optimum temperature for MU did not differ between sites despite the differences in the climate. However, the optimal soil water content for the relative maximum MU decreased with increasing mean annual temperature at the sites.
These results point to site-specific adaptation of the microbial community that governs the sensitivity of Rh to temperature, but not soil moisture and the dependency of MU to soil moisture alone. We would also like to discuss how this insight can be used to inform ecosystem models.

How to cite: Hessilt, T., Lyberth Hauptmann, D., and Riis Christiansen, J.: Response of heterotrophic respiration and oxidation of atmospheric CH4 to changes in soil moisture and temperature in drylands across a global climate and ecosystem gradient, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18064, https://doi.org/10.5194/egusphere-egu2020-18064, 2020.

Respiration pulses at rewetting are prominent features of soil responses to soil moisture fluctuations. These pulses are much larger compared to respiration rates under constant soil moisture, pointing to variations in water availability as drivers of the enhanced CO₂ production. Moreover, the respiration pulses tend to be larger when soil moisture before rewetting is lower. Thus, both the pre-rainfall soil moisture and the variation in soil moisture control the size of the respiration pulse. While these patterns are known from empirical studies, models have struggled to capture the relations between rainfall statistical properties (frequency of occurrence and rain event depths) and the occurrence and size of respiration pulses, framing the scope of this contribution. Specifically, we ask – how are the statistical properties of respiration pulses related to rainfall statistics?

Because rainfall can be regarded as a stochastic process generating variations in soil moisture, also respiration pulses at rewetting can be modelled through a probabilistic model. Here we develop such a model based on the premises that rainfall can be described as a marked Poisson process, and that respiration pulses increase with increasing variations of soil moisture (i.e., larger pulses after larger rain events) and decreasing pre-rain soil moisture (i.e., larger pulses after a long dry period). This model provides analytical relations between the statistical properties of soil respiration (e.g., long-term mean and standard deviation) and those of rainfall, allowing to study in a probabilistic framework how respiration varies along existing climatic gradients or in response to climatic changes that affect rainfall statistics.

Results show that the long-term mean CO₂ production during respiration pulses increases with increasing frequency and depth of rainfall events. However, the relative contribution of respiration pulses to the total microbial respiration decreases with rainfall frequency and depth. Similarly, also the variability of the size of respiration pulses, as measured by their standard deviation, decreases with increasing rainfall frequency and depth. As a consequence, climatic changes exacerbating rainfall intermittency – longer dry periods and more intense rain events – are predicted to increase both the relative contribution of respiration pulses to total microbial respiration and the variability of the pulse sizes.

How to cite: Manzoni, S., Chakrawal, A., Fischer, T., Porporato, A., and Vico, G.: Modelling respiration pulses at rewetting as a stochastic process, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3736, https://doi.org/10.5194/egusphere-egu2020-3736, 2020.

Terrestrial biogeochemical cycles are regulated by soil microorganisms. The microbial carbon release due to respiration and carbon sequestration through microbial growth determine whether soils become sources or sinks for carbon. Temperature i​s one of the most important environmental factors controlling both microbial growth and respiration. Therefore, to understand the influence of temperature on microbial processes is crucial. One strategy to predict how ecosystems will respond to warming is to use geographical ecosystem differences, in space-for-time (SFT) substitution approaches. We hypothesized (1) that microbes should be adapted to their environmental temperature leading to microbial communities with warm-shifted temperature relationships in warmer environments, and vice versa. Furthermore, we hypothesized  (2) that other factors should not influence microbial temperature relationships, and (3) that the temperature sensitivity of microbial processes (Q10) should be linked to the microbial temperature relationships.

In this project, we investigated the effects of environmental temperature on microbial temperature relationships for microbial growth and respiration along a natural climate gradient along a transect across Europe to predict the impact of a warming climate. The transect was characterized by mean annual temperature (MAT) ranging from - 4 degrees Celsius (Greenland) to 18 degrees Celsius (Southern Spain), while other environmental factor ranges were broad and unrelated to climate, including pH from 4.0 to 8.8, C/N ratio from 7 to 50, SOM from 4% to 94% and plant communities ranging from arctic tundra to Mediterranean grasslands. More than 56 soil samples were analyzed and microbial temperature relationships were determined using controlled short-term laboratory incubations from 0 degrees Celsius to 45 degrees Celsius. The link between microbial temperature relationship and the climate was assessed by using the relationship between the environmental temperature and indices for microbial temperature relationships including the minimum (T_min), optimum (T_opt) and maximum temperature (T_max) for microbial growth as well as for respiration. To estimate the T_min, T_opt and T_max the square root equation, the Ratkowsky model was used.

We found that microbial communities were adapted to their environmental temperature. The microbial temperature relationship was stronger for microbial growth than for respiration. For 1 degrees Celsius rise in MAT, T_min increased 0.22 degrees Celsius for bacterial and 0.28 degrees Celsius for fungal growth, while T_min for respiration increased by 0.16 per 1 degrees Celsius rise. T_min was also found to be universally linked to Q10, such that higher T_min resulted in higher Q10. Other environmental factors (pH, C/N ratio, SOM, vegetation cover) did not influence the temperature relationships. By incorporating the determined relationships between environmental temperature and microbial growth and respiration into large scale ecosystem models, we can get a better understanding of the influence of microbial adaptation to warmer climate on the C-exchange between soils and atmosphere.

How to cite: Tajmel, D., Cruz Paredes, C., and Rousk, J.: Do microbial communities adapt to the temperature of their climate?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-776, https://doi.org/10.5194/egusphere-egu2020-776, 2020.

Human activities have caused global warming by 0.95 °C since the industrial revolution, and average temperatures in Austria have risen by almost 2 °C since 1880. Increased global mean temperatures have been reported to accelerate carbon (C) cycling, but also to promote nitrogen (N) and phosphorus (P) dynamics in terrestrial ecosystems. However, the extent of warming-induced increases in soil C, N and P processes can differ, causing an eventual uncoupling of biogeochemical C, N and P cycles, and leading to altered elemental imbalances between available plant and soil resources and soil microbial communities. The altered dynamics in soil C and nutrient availability caused by increased soil temperature could shift the growth-limiting element for soil microorganisms, with strong repercussions on the decomposition, mineralization and sequestration of organic C and nutrients. The latter relates to the conservative cycling of limiting elements while elements in excess are mineralized and released at greater rates by microbial communities.

Despite the many laboratory and in situ studies investigating factors that limit soil microbial activity, most of them explored nutrient addition effects on soil respiration or soil enzyme activities. A critical assessment, however, clearly indicated the inappropriateness of these measures to deduce growth-limiting nutrients for soil microbes. Similar to studies of plant nutrient limitation, unequivocal assessment of soil microbial element limitation can only be derived from the response of microbial growth to element amendments. To our knowledge this has not been performed on soils undergoing long-term soil warming.

In this study, we therefore investigated the effect of long-term soil warming on microbial nutrient limitation based on microbial growth measurements in a temperate calcareous forest soil. Soil samples were taken from two soil depths (0-10, 10-20 cm) in both control and heated plots in the Achenkirch soil warming project (>15 yrs soil warming by + 4 °C). Soil samples were pre-incubated at their corresponding field temperature after sieving and removal of visible roots. The soils were amended with different combinations of glucose-C, inorganic/organic N and inorganic/organic P in a full factorial design, the nutrients being dissolved in ¹⁸O-water. After 24 hours of incubation, microbial growth was measured based on the ¹⁸O incorporation into genomic DNA. Nutrient (co)limitation was determined by comparing microbial growth responses upon C and nutrient additions relative to unamended controls. Basal respiration was also measured based on the increase in headspace CO₂, allowing to estimate microbial C use efficiency (CUE). The fate of C and nutrient amendments was finally traced by measurements of inorganic and organic extractable and microbial biomass C, N and P. This study will thereby provide key insights into potential shifts in limiting nutrients for microbial growth under long-term soil warming, and into concomitant effects on soil C and nutrient cycles.

How to cite: Shi, C., Malo, C. U., Tian, Y., Zhang, S., Heitger, M., Kengdo, S. K., Borken, W., Heinzle, J., Schindlbacher, A., and Wanek, W.: Does long-term soil warming affect microbial element limitation? A test by short-term assays of microbial growth responses to labile C, N and P additions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11341, https://doi.org/10.5194/egusphere-egu2020-11341, 2020.

Global warming may accelerate soil carbon (C) and nutrient cycling as higher temperatures accelerate soil microbial and enzymatic activities. However, this enhanced soil C cycling can diminish with time due to the depletion of labile soil C or due to thermal acclimation of soil microbes, while the increased N cycling may be dampened over time in N-rich soils. Moreover, soil climate as well as the quality and quantity of plant inputs change between seasons, which could influence the C: nitrogen (N): phosphorus (P) stoichiometry of resources available for microbes and thereby alter the warming effect on microbial activities and nutrient cycling between seasons. Such seasonal changes caused inconsistent warming effects on extracellular enzyme activities and on soil respiration in some experiments, with warming effects turning from positive to negative between seasons, yet the underlying controls of these adverse effects are far from being well understood. In this study, we therefore aimed to investigate soil warming and seasonal effects on soil C, N, and P pools and processes in a temperate calcareous mixed forest. We collected soil samples in spring, summer and fall (May, August, and October 2019) from a long-term (>15 yrs) soil warming experiment in Achenkirch, Northern Limestone Alps, Austria (47°34’ 50’’ N; 11°38’ 21’’ E; 910 m a.s.l.). The samples were incubated at the corresponding in-situ temperatures in the laboratory. Microbial growth, respiration and C use efficiency were determined by following ¹⁸O-H₂O incorporation in DNA and by gas analysis. ¹⁵N pool dilution assays were applied to quantify gross rates of protein depolymerization, N mineralization, and nitrification, whilst gross rates of soil inorganic P mobilization were measured by a ³³P pool dilution assay. Moreover, we measured the potential soil enzyme activities of four hydrolases and two oxidases, and determined contents of labile (extractable) and microbial biomass C, N, and P. This study will thereby provide a comprehensive insight into how soil warming influences soil microbial C, N, and P cycling in a temperate calcareous mixed forest as well as into their energetic, stoichiometric and soil microclimatic constraints. The long-term nature of this soil warming experiment will therefore allow predictions of the future biogeochemical behavior of calcareous forest soils, and deduce potential feed-backs on forest productivity, atmospheric composition and climate change.

How to cite: Tian, Y., Urbina Malo, C., Shi, C., Zhang, S., Heitger, M., Kwatcho Kengdo, S., Borken, W., Heinzle, J., Schindlbacher, A., and Wanek, W.: Changes in soil warming effects on microbial C, N and P cycling across seasons in a temperate calcareous mixed forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11362, https://doi.org/10.5194/egusphere-egu2020-11362, 2020.

Soils store more carbon than the atmosphere and total land plant biomass combined. Soil organic matter (SOM) can be classified into different physical pools characterized by their degree of protection and turnover rates. Usually, these pools are isolated by dividing soils in different water-stable aggregate size classes and, inside these classes, SOM fractions with differing densities and properties: Stable mineral-associated organic matter (MOM) and labile particulate organic matter (POM). Increasing temperatures are known to initially enhance microbial decomposition rates, releasing C from soils which could further accelerate climate change. The magnitude of this feedback depends on which C pool is affected the most by increased decomposition. Since MOM, thought to be the best protected carbon pool, holds most of the soil C, losses from this pool would potentially have the biggest impact on global climate. Experimental results are inconclusive so far, as most studies are based on short-term field warming (years rather than decades), leaving the ecosystem response to decades to century of warming uncertain.

We made use of a geothermal warming platform in Iceland (ForHot; https://forhot.is/) to compare the effect of short-term (STW, 5-8 years) and long-term (LTW, more than 50 years) warming on soil organic carbon and nitrogen (SOC, SON) and its carbon and nitrogen isotope composition (δ¹³C and δ¹⁵N) in soil aggregates of different sizes in a subarctic grassland. OM fractions were isolated via density fractionation and ultrasonication both in macro- and microaggregates: Inter-aggregate free POM (fPOM), POM occluded within aggregates (iPOM) and MOM.

MOM, containing most of the SOC and SON, showed a similar response to warming for both macro- and microaggregates. Compared to LTW plots, STW plots overall had higher C and N stocks. But warming reduced the carbon content more strongly in STW plot than in LTW plots. δ¹³C of MOM soil increased with temperature on the STW sites, indicating higher overall SOM turnover rates at higher temperatures, in line with the higher SOC losses. For LTW, δ¹³C decreased with warming except for the most extreme treatment (+16°C). Warming duration had no impact on iPOM-C. fPOM-C decreased in STW sites with increasing temperature, while it increased on the LTW sites.

Overall our results demonstrate warming-induced C losses from the MOM-C-pool, thought to be most stable soil carbon pool. Thus, warming stimulated microbes to decompose both labile fPOM and more stable MOM. After decades of warming, C losses are less pronounced compared to the short-term warmed plots, pointing to a replenishment of the carbon pools at higher temperatures in the long-term. This might be explained by adaptations of the primary productivity and/or substrate-limitation of microbial growth.

How to cite: Mohrlok, M., Martin, V., Verbrigghe, N., Fuchslueger, L., Poeplau, C., Sigurdsson, B. D., Janssens, I., and Richter, A.: The influence of short-term and long-term warming on physical soil carbon pools , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18383, https://doi.org/10.5194/egusphere-egu2020-18383, 2020.

Forests are the main contributors to the global terrestrial carbon (C) sink but several studies suggest that global warming could significantly reduce their CO₂ mitigation potential. The capacity of forest plants to sequester C is closely linked to soil nitrogen (N) availability, a major control of plant growth and ecosystem functioning. An increase of soil temperature caused by global change is critically affecting soil N supply rates, both directly by increasing diffusive N fluxes in the soil solution and indirectly by accelerating soil N turn-over rates. In recent short-term laboratory incubation studies, an increase in soil temperature has not only led to a significant increase in diffusive N fluxes but also to a concomitant shift in N quality available for plant uptake towards a higher portion of inorganic N forms compared to small organic N forms such as amino acids. However, until now long-term effects of soil warming on soil N fluxes have not been studied. Here, we present first results from a study on soil N availabilities at the long-term soil warming experimental site Achenkirch (Austria) in the Limestone Alps. This site is one of the few in situ climate manipulation experiments operational for more than 10 years and has already provided a wealth of novel insights into the potential effects of global warming on forest ecosystem responses. Applying in situ microdialysis, we estimated diffusive fluxes of inorganic N and amino acids along the growing season in soils warmed by resistance heating cables since 2005 (+4 °C compared to control plots) and control soils. Fluxes of all N forms were highly variable within each subplot (2 x 2 m) and reflected the high heterogeneity of soils at this forest site. Interestingly, fluxes of amino acids were less variable than of nitrate or ammonium throughout the year, indicating comparably stable protein depolymerization rates. In summary, long-term soil warming affected diffusive N fluxes but less than other factors operating on smaller (< 1 cm) scales.

How to cite: Inselsbacher, E., Heinzle, J., and Schindlbacher, A.: Effects of long-term soil warming on nitrogen fluxes in forest soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7551, https://doi.org/10.5194/egusphere-egu2020-7551, 2020.

The intense use of fertilisers for agricultural and forest management purposes as well as atmospheric nitrogen (N) deposition has changed ecosystem stoichiometry in some parts of the planet, drawing great attention to the long-term impacts of N additions on carbon (C) sequestration. Soil organic matters (SOMs) are the major sink of C in terrestrial ecosystems and hence it is essential to understand the impacts of N addition on SOM not only quantitatively but also qualitatively. In temperate and boreal forests, chronic N addition generally suppresses SOM decomposition and increases C accumulation. The potential mechanisms for this have long been discussed and yet to be unearthed.

Here, we examined the impacts of long-term N addition on the chemical composition of SOMs in boreal forests situated in northern Sweden under two vegetation types (Norway spruce or Scots pine) and a range of N addition regimes where N addition rates varied between 3 and 70 kg N ha^-1 year^-1, duration between 12 and 32 years and total added amount between 50 and 2000 kg N ha^-1. Soil samples were collected from the organic layer (litter and humus layers) and analysed for the chemical composition of SOMs using two metrics: pyrolysis gas chromatography–mass spectrometry (GC/MS) and solid-state ¹³C nuclear magnetic resonance spectroscopy (¹³C-NMR).

We found that the chemical composition of SOMs shifted with soil C:N ratios regardless of vegetation types, or duration and rates of N addition. Preliminary results suggest that the observed shift in chemical composition in SOMs may have been attributed to altered decomposition of lignin and carbohydrate-derived compounds. This was in line with previous research conducted in the same study sites that demonstrated added-N enhanced non-enzymatic brown-rot lignin oxidation relative to enzymatic white-lot lignin mineralisation. Here, the comprehensive examination of SOM chemical composition demonstrates altered molecular characteristics of SOMs with soil C:N conditions. This may help us to elucidate the mechanisms by which N addition alters the balance of decomposition and accumulation of SOMs.

How to cite: Hasegawa, S., Marshall, J., Näsholm, T., and Bonner, M.: The impacts of long-term, high intensity N addition on the chemical composition of soil organic matter in a boreal forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19555, https://doi.org/10.5194/egusphere-egu2020-19555, 2020.

The western Amazon is particularly sensitive to drought since precipitation is common even during "dry season". The combination of increasing land use pressure and droughts due to climate change makes the scenario of this ecosystem likely to cross or having crossed tipping points. We argue that nitrous oxide (N₂O) emissions can be used to identify the crossing of tipping points in soils, particularly those related to N-cycling. This hypothesis is being tested within the BMBF funded Project PRODIGY, which will show that under stress microbial functional diversity in soils are a safety-net for ecosystems. The survey area (MAP) spreads across three countries (Peru, Brazil and Bolivia). Lab and field experiments are used to test our hypothesis based on the observations that N₂O emission under tropical pasture shift after 10 years in use. Pre-measurement modeling is used to optimize measurement designs. Replicated above-ground biodiversity levels (n=4) will be sampled in each country. The soil will also be used for lab drought manipulation experiments to unravel underlying mechanisms. Measured values have shown to be lower than expected and simulated rates. Maybe because tipping points at different spacial and temporal scales are crossed faster than in temperate regions and biogeochemistry is less understood? Results from this investigation will allow the improvement of N₂O models for tropical soils.

How to cite: Kilian Salas, S., Díaz García, E., Andrino, A., Meurer, K. H. E., Boy, D., Horn, M., Boy, J., and Jungkunst, H.: Using N2O to detect if a tipping point has been crossed in tropical soils after droughts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18405, https://doi.org/10.5194/egusphere-egu2020-18405, 2020.

Large forest fires are expected to occur more frequently in some areas in the Iberian Peninsula with the current climate change predictions. Post-fire soil erosion is an important issue because of its potential large impact on soil carbon stocks and functioning. Addition of mulching to burnt soils has been proved as an effective measure to reduce post-fire erosion. This measure could also increase the stability of microbial activity to drought events, which are also expected to be more frequent in the region.

This study analyzes the response of three measurements of soil microbial activity (dehydrogenase activity, respiration rates and DNA concentration, as an index of microbial biomass) to a drying-rewetting cycle in soils that were burnt during large wildfires and that have been treated with different mitigation measures to prevent post-fire erosion.

Soil samples were collected from two field experiments on post-fire mitigation in Portugal, one in a Maritime Pine plantation over a Humic cambisol and one in a Strawberry tree stand over a Umbric leptosol. These sites were affected by large wildfires in june and october 2017, respectively. At the pine site, three treatments were compared: 1) control plots, where no treatment was applied and post-fire erosion rates were highest; 2) SM plots (Spontaneuos Mulching), in which spontaneous needle cast from the scorched pine crowns occurred (at an average rate of 0.5 kg m^-2); 3) HM plots (Human Mulching), in which pine needles (were applied manually at a rate of 0.2 kg m^-2. In addition, a nearby unburned Maritime Pine plantation was sampled (Unburnt). At the Strawberry tree site, control plots were compared with plots mulched with wheat straw (WM) at an application rate of 0.2 kg m^-2. Sampling involved the organic surface horizon as well as the upper 15 cm of the Ah horizon.

Samples were preincubated during 28 days at 25°C and at 70% of field capacity. Afterwards, they were divided into two sets; one set was subjected to a drought event for 30 days that reduced soil moisture contents to 5-10% of field capacity. Subsequently, the drought replicates were rehydrated until they reached their initial moisture content, which was maintained for 14 days.

Dehydrogenase activity differed significantly between the burnt and unburnt soils, both for the drying and the re-wetting period. The burnt soils generally were more vulnerable to the drought episode than the unburnt soil. By contrast, dehydrogenase activity did not reveal significant impacts of the different mulching treatments compared to the untreated burnt soils. This was the case for both the organic surface horizon and the subsurface horizon. Respiration rates and DNA concentrations revealed basically the same results.

The three indicators of microbial activity studied here discriminated between burnt and unburnt soils, but they did not suggest any significant improvement in the response to drought by any of the post-fire emergency stabilization measures. Further research on the impacts of such measures on the resistance and resilience of microbial activity to drought should consider other soil quality indicators such as labile organic matter fractions.

How to cite: Fernández Boy, E., Herrador, M. B., Ordoñez, V., Morales, L., González-Pelayo, O., Keizer, J. J., and Domínguez, M. T.: Effects of a simulated drying-rewetting cycle on microbial activity in soils degraded by post-fire erosion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10376, https://doi.org/10.5194/egusphere-egu2020-10376, 2020.

Climate change will increase temperatures and the frequency and intensity of extreme drought and rainfall events. When a drought period is followed by a rainfall event, there is a big CO₂ pulse from soil to the atmosphere which is regulated by soil microorganisms. In the present study, we set out to investigate how simulated drought and warming affects the soil microbial responses to drying and rewetting (DRW), and how those responses will interact with the level of land degradation. Previous work has shown that exposure DRW cycles in the laboratory and in the field can induce changes in the microbial community such that it resumes growth rates faster after a DRW cycle. In addition, it has been observed that a history of drought in both a humid heathland ecosystem in Northern Europe and in semi-arid grasslands in Texas can select for microorganisms with a higher carbon use efficiency (CUE) during DRW. In this study we tested if these observations could be extended to subtropical environments.

Rain shelters and open top chambers (OTC) were installed in Northwestern Ethiopia in two contrasting land-uses; a degraded cropland and a pristine forest. Soils were sampled (>1-year field treatments) and exposed to a DRW cycle in the laboratory. Microbial growth and respiration responses were followed with high temporal resolution over 3 weeks. We hypothesized that (i) simulated drought would result in more resilient and efficient microbial communities to DRW, while (ii) simulated warming should leave microbial community traits linked to moisture unchanged. In addition, (iii) we hypothesized that microbial communities would recover growth rates faster in the cropland since that ecosystem is more prone to DRW events.

Microbial responses in both land-uses and treatments universally showed a highly resilient type of community response with both bacterial growth and fungal growth increasing immediately upon rewetting, linked with the expected respiration pulse. The field treatments simulating drought and warming did not affect the already high resilience of soil microbial communities to DRW cycles. However, differences between the rates of recovery between fungi and bacteria were observed. Fungal growth recovered faster than bacterial growth, peaking c. 15 h in comparison to bacteria that peaked at c.20h after rewetting. Simulated drought reduced the microbial CUE during rewetting in croplands without affecting the forest soils. The CUE was also elevated in the warming treatments in both land-uses, and generally higher in croplands than in forest soils. Taken together, the responses in microbial CUE during the rewetting of dry soils were likely linked to either (i) differences in resource availability which were higher in warming treatments and in croplands compared to forests, or (ii) selection of  more efficient microbial communities due to a higher exposure to DRW events driven by the higher temperatures in the cropland, and increased evapotranspiration in the warming treatments.

How to cite: Leizeaga, A., Hicks, L. C., Brangarí, A. C., Wondie, M., Sandén, H., and Rousk, J.: Effects of simulated drought and warming on microbial responses to drying and rewetting in contrasting land-uses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1180, https://doi.org/10.5194/egusphere-egu2020-1180, 2020.

Drying and rewetting events induce enormous dynamics in soil biogeochemistry, known as the “Birch effect”. A series of laboratory studies have shown that during this phenomenon, respiration and microbial growth are uncoupled. In addition, it has been found that soil microorganisms exhibit one of two different response-patterns, the dynamics of which are strongly regulated by the harshness of the moisture disturbance experienced by soil microbes. Despite the potential significance of these responses for the global carbon cycle, the characteristics and mechanisms underlying them are still unclear.

In order to shed some light on the current status of research in this field, we will present the outcomes of an international workshop organized in Lund in November 2019. During it, we integrated researchers from different environments in order to identify knowledge-gaps and tackle outstanding and new challenges in this field. We will review the characteristics of the growth and respiration responses to moisture fluctuations and the putative mechanisms and factors governing them. We will also discuss the advantages of combining empirical and modelling approaches by using our own group experience as a case example.

How to cite: Brangarí, A. C., Hicks, L., Leizeaga, A., and Rousk, J.: Current knowledge and future perspectives on soil drying and rewetting, by the scientific community, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20220, https://doi.org/10.5194/egusphere-egu2020-20220, 2020.

Climate change is exposing terrestrial ecosystems to more extreme drought and rainfall events, resulting in an increased frequency and intensity of drying-rewetting (D/RW) events in soils. Rewetting a dry soil induces enormous dynamics in both microbial growth and biogeochemistry, including a large pulse of CO₂ release to the atmosphere. Upon D/RW, two different microbial growth responses have been identified; a more resilient response where bacteria start growing immediately with a quick recovery after rewetting and a less resilient response where there is a lag-period of up to 30 hours of near-zero growth before bacteria start to grow. The resilience of microbial growth following D/RW has important implications for the ecosystem C budget, since an extended lag-period of no growth during a time of high CO₂ release will result in net soil C loss. In natural systems, it has been found that a legacy of drought led to a more resilient bacterial growth response upon rewetting, with a reduced lag-period before the onset of growth. Exposing soils to repeated cycles of D/RW in the laboratory has also been shown to shift bacterial growth responses to a more resilient type. We hypothesised that this shift in response is explained by selection for a microbial community which is quick at colonizing the labile C resources made available upon D/RW.  

In order to test our hypothesis, we pre-treated soils by exposing them to either (i) three cycles of D/RW, (ii) three pulses of glucose addition or (iii) three pulses of litter addition. The substrate additions were used to simulate the labile C release in soils during D/RW, thereby enabling us to investigate if the colonization of new substrate is the causal mechanism explaining the observed shift in bacterial resilience in soils with a history of D/RW. The pre-treated soils – along with an unamended control soil – were then exposed to the same D/RW event, with bacterial growth, fungal growth and respiration responses measured at high temporal resolution over 4 days. As previously reported, exposing the soil to a series of D/RW events resulted in a more resilient bacterial growth response, with the lag-period reduced from ca. 30 hours to an immediate initiation of growth. Pre-treating the soils with glucose reduced the lag-period before the onset of bacterial growth by ca. 50% whereas pre-treatment with litter induced only a marginally (< 10%) more resilient bacterial growth response to D/RW. Interestingly, pre-treatment of the soils with glucose and litter both induced a more resilient fungal growth response, with the responses resembling the shift in fungal resilience induced by exposing the soils to repeated cycles of D/RW. Overall, our results show that selection for quick colonizers partly explains the shift to more resilient microbial growth in soils exposed to repeated D/RW events, but further investigation is required to identify additional factors contributing to the shift in resilience.

How to cite: Hicks, L., Lin, S., and Rousk, J.: Is microbial resilience to drying-rewetting driven by selection for quick colonizers? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16648, https://doi.org/10.5194/egusphere-egu2020-16648, 2020.

The influence of drought on terrestrial carbon cycling has received great attention because of the increasing frequency of extreme drought events in climate scenarios. In the CLIMAITE experiment, we have exposed plots to reduced precipitation since 2006. During the first years, precipitation was only reduced for 4-6 weeks during spring/early summer. In order to increase our focus on finding thresholds for functional and structural change in the ecosystem, the experiment was redesigned towards more extreme manipulations in June 2016 using a new gradient design continuously removing 40, 50, and 66% of ambient precipitation with permanent rainout shelters.

Rates of net ecosystem exchange (NEE), ecosystem respiration (R_E) and soil respiration (Rs) are measured inside treatment plots using an LI-6400 connected to a custom-built 210L transparent chamber (for NEE) that can be darkened (for RE) as well as a 1L dark chamber (for Rs). In addition, environmental variables such as soil temperature, precipitation, soil water content and photosynthetically active radiation (PAR) are recorded continuously at the plot or site level. In addition, soil cores from the different treatments will be collected and analyzed for soil substrate (e.g. soil organic carbon) and incubated in the lab for analysis of Q₁₀.  Using the observations from the field and the lab together we will develop a new multiple regression model to fit the CO₂ fluxes under severe precipitation removal treatments.

To obtain more reliable and accurate estimates of the seasonal and annual responses of soil carbon flux exchange under precipitation change scenarios, the change in soil water content and temperature, the soil substrate availability as well as the variation of the frequency and timing of precipitation events are included in the carbon flux model. The fitting of models to the observational data will reveal if functional/structural thresholds for the carbon exchange have been exceeded in the ecosystem, thus providing novel experimental and modeling evidence for such thresholds.

How to cite: Li, Q., Larsen, K. S., and Gundersen, P.: Long-term effects of precipitation removal manipulations on soil carbon balance and exchange in a Danish heathland/grassland ecosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13404, https://doi.org/10.5194/egusphere-egu2020-13404, 2020.

Soil gases are efficient messengers of the subsurface biogeochemical processes that underlie important nutrient cycles.  Recent advances in subsurface gas sampling techniques can be combined with high precision trace gas instrumentation to yield novel insights into these processes and their mechanisms.

We present measurements of a wide range of trace gases before, during, and after a simulated rainfall upon northeastern US temperature forest soil in meso-scale columns.  Subsurface concentrations and above-ground fluxes of N₂O and its isotopes, CH₄ and its isotopes, CO₂, NO, NO₂, NH₃, and a wide range of volatile organic compounds (e.g. monoterpenes, sesquiterpenes, isoprene, acetonitrile, aromatics) were quantified in real time with 30 minute temporal resolution.  Small molecules were measured using Aerodyne TILDAS instruments, while VOCs were measured using a Vocus mass spectrometer.

Addition of water to the dried soil column produced a classic Birch effect pulse of both C and N species, including for VOCs.  We explore correlations between responses of trace gases above- and below-ground, and relate the small molecule pulses to the larger VOC responses.  In addition, we demonstrate the value of isotopic signatures for these studies, with the observation of fast, large isotopic shifts in the ¹⁵N₂O isotopomers.  We compare these isotopic signatures to simple kinetic models to provide insight into the mechanisms underlying the nitrogen Birch effect.

How to cite: Roscioli, J., Shorter, J., Krechmer, J., Meredith, L., and Gil Loaiza, J.: Exploring The Birch Effect In The Subsurface Using Diffusive Soil Probes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12125, https://doi.org/10.5194/egusphere-egu2020-12125, 2020.

Soil nutrient availability is essential for adequate crop production and drought conditions that result in abnormally low amounts of precipitation for extended periods of time have a substantial impact on soil microbial activity and therefore nutrient cycling. The northern Great Plains region of the USA suffered an extended period of time in which effective precipitation for crop production was severely reduced and based on the USA Drought Monitor the drought during the growing season from April through October 2017 was classified as exceptional drought. At the NDSU – Dickinson Research Extension Center, a long-term integrated system that includes a diverse multi-crop rotation (spring wheat, cover crop, corn, pea-barley intercrop, and sunflower), beef cattle grazing of the pea-barley, corn, and a 13-specie cover crop within the rotation, is being utilized to monitor the effects soil microbial and fungal activity have on production over time and space in this crop and animal production system. Moreover, the overall effects of increased soil health indices on production are being monitored. Research results have previously been reported showing that soil organic matter (SOM) mineralization has resulted in reduced nitrogen fertilizer application. Regression analysis of SOM and potential nitrogen mineralization suggests that 8.4 mg N/kg are mineralized for each 1% increase in SOM. However, during periods of restricted precipitation on rain-fed crops, soil microbial respiration and fungal activity are negatively impacted, and crop production and animal grazing days are sharply reduced. Soil microbial biomass was correlated to overall production with the exception of spring wheat in rotation which may be due to increased water use by the previous crop (sunflower). Further analysis indicated that most soil microbial organisms recovered two years post drought with the exception of Rhizobia spp. populations which did not recover two years post drought. However, compared to the pre-drought 2016 production year, overall crop production yields had not fully recovered by 2019. Compared to the 2016 crop production, overall crop production in the rotation was reduced 64% in 2017, recovered to 54% of 2016 in 2018, and recovered to 66% of 2016 by the 2019 crop year. Whether crop yields are on par with 2016 by the end of the 2020 crop year is still to be determined. These yield observations point to the amount of time needed to fully recover from the long-term effects of exceptional drought on crop production.

How to cite: Senturklu, S., Landblom, D., and Steffan, J.: Effect of Drought and Recovery on Microbial, Fungal, and Crop Response in a Diverse Multi-Crop Rotation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12151, https://doi.org/10.5194/egusphere-egu2020-12151, 2020.

Climatic and plant community changes are observed in the alpine belt of the Teberda Reserve (the Northwest Caucasus) in the last decades. Increase of average monthly temperature in the summer months in 2006-2018 was 1.8-2.2 ºC in comparison with 1966-1990. For the last 13 years, the maximum temperature in July and August reached 22.1-23.2 ºC vs. 20.5 ºC in 1966-1990, and minimum temperature during these months did not fall lower than -1.8 ºC whereas in 1966-1990 it fell up to -7.0 ºC. At the same time decrease of summer precipitation, especially in July and August is observed (average 80-100 mm per month vs. 150-160 mm in 1966-1990). Against this climatic background, a significant increase of dwarf shrub with ericoid mycorrhizal symbiosis (Vaccinium vitis-idaea) occurs in plant community of alpine lichen heath. As ericoid mycorrhiza is characterized by high enzymatic activity capable to transform and mobilize soil organic matter, we assume that the appearance of Vaccinium vitis-idaea in grass ecosystems can change soil properties. Simultaneously the observed tendency to decrease the amount of summer atmospheric precipitation in mountain regions can change soil moisture which is also highly important to control soil microbial activity and organic matter transformation.

The properties of the mountain-meadow soil of the alpine lichen heath, characterizing labile forms of carbon, nitrogen and phosphorus, as well as biological activity at different soil moisture and in the presence or absence of Vaccinium vitis-idaea in the plant community, have been studied. It has been shown that under V. vitis-idaea soil is characterized by greater acidity and less responsive to changes in soil moisture. Differences in properties in the presence and absence of V. vitis-idaea are predominantly determined by the expressed response of the soil to changes in moisture in the absence of dwarf shrub. Under herbal vegetation, when soil moisture decreases, concentrations of inorganic nitrogen, activity of N-mineralization and nitrification, microbial biomass and soil respiration decrease, but concentrations of labile organic carbon and nitrogen, and enzymatic activity increase. Such changes indicate a shift in organic matter transformation from mineralization to depolymerization, more characteristic of ectomycorrhizal and ericoid mycorrhizal dominated ecosystems. Thus, both factors (soil moisture and invasions of ericoid mycorrhizal plant species) should be taken into account in predicting changes of alpine ecosystems functioning.

This study was supported by Russian Science Foundation (16-14-10208).

How to cite: Makarov, M., Malysheva, T., Kadulin, M., and Sabirova, R.: Vaccinium vitis-idaea decreases the dependence of alpine soil properties from soil moisture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20312, https://doi.org/10.5194/egusphere-egu2020-20312, 2020.

Beef cattle grazing, soil microbial respiration, and Rhizobia spp. populations serve important roles in soil nutrient cycling and during periods of drought, when abnormal precipitation declines, forage production for animal grazing and performance are negatively impacted. Soil nutrient availability is essential for adequate crop production and extended drought reduces soil microbial activity and therefore nutrient cycling. During the 2017 growing season between April and October in the northern Great Plains region of the USA, effective precipitation for crop production and animal grazing was severely reduced due an exceptional drought as classified by the US Drought Monitor. At the NDSU – Dickinson Research Extension Center, Dickinson, North Dakota, USA, a long-term integrated system that includes yearling steer grazing within a diverse multi-crop rotation (spring wheat, cover crop, corn, pea-barley intercrop, and sunflower). Within the rotation of cash and forage crops, beef cattle graze the pea-barley, corn, and cover crop (13-specie) within the rotation and is being utilized to monitor the effects of animal, microbial and fungal activity over time and space in the crop and animal production system. Nitrogen fertilizer has been replaced in the system by soil microbial and fungal activity (Potential Mineralizable Nitrogen: 8.4 mg N/kg) such that for each 1% increase in SOM there is a corresponding increase of 18.8 kg of potential nitrogen mineralized per ha. Animal grazing days are severely reduced when precipitation is inadequate for soil microbial respiration to occur. What is even more concerning, when relying on microbial activity to supply plant nutrients, is recovery time for microbial activity to fully recover from exceptional drought as was the case in this research project. Compared to the 2016 crop production year that preceded the 2017 drought, cover crop (13-specie), pea-barley, and corn yields were reduced 86, 33, and 64% during the 2017 drought. This decline in crop production reduced the number of days of grazing by an average 50% and average daily gains were also reduced. Steer average daily gains were 1.05 0.95, and 0.83 kg/steer/day in 2017 when grazing pea-barley, corn, and cover crop, respectively. For this research that relies on soil derived plant nutrients soil analysis for microbial and Rhizobia spp. biomass began recovery in 2018 and continued into 2019 as evidenced by large percentage increases in organism biomass; however, complete production recovery did not occur by the end of the 2019 grazing season in which days of grazing were reduced compared to the 2016 grazing season. Biological animal, crop, microbial, fungal, and nutrient replacement recovery will be presented in the poster.

How to cite: Landblom, D. and Senturklu, S.: Effect of Drought and Recovery on Grazing Animal, Microbial, and Fungal Response in a Diverse Multi-Crop Rotation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20195, https://doi.org/10.5194/egusphere-egu2020-20195, 2020.

Changes in climate and land-use are altering soil respiration patterns and thus affecting C sequestration rates globally. This study aims to understand the effect of revegetation induced land-use change on the response of soil respiration to precipitation pulses during an extreme-drying-and-rewetting period. Soil respiration (SR) in cropland, grassland, shrubland, and orchard were intensively monitored along with environmental variables during an extreme drought period with precipitation pulse on China’s Loess Plateau. SR was strongly correlated to soil water content for all land-uses. However, the relationship was highly dependent on land-use types: SR was only strongly suppressed in cropland and orchard when moisture content exceeded 10.8% and 13.7%, respectively, whereas no clear suppression was observed under other land-uses. As a result, the C loss in grassland and shrubland was 49.1-78.9% higher than in cropland following significant precipitation events. In addition, SR was negatively and weakly correlated with soil temperature, indicating the change in the dominant control on SR due to extreme drought. Land-use change alters the response of soil respiration to soil moisture during extreme-drying-and-rewetting periods in this revegetated ecosystem. Its effect on respiration pulses will amplify as extreme climate events increase in the future, which may potentially alter the existing C balance.

How to cite: Sun, W.: Revegetation modifies patterns of temporal soil respiration responses to extreme-drying-and-rewetting in a semiarid ecosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6591, https://doi.org/10.5194/egusphere-egu2020-6591, 2020.

The Air Stagnation Index (ASI) is a vital meteorological measure of the atmosphere’s ability to dilute air pollutants. The original metric adopted by the US National Climatic Data Center (NCDC) is found to be not very suitable for China, because the decoupling between the upper and lower atmospheric layers results in a weak link between the near-surface air pollution and upper-air wind speed. Therefore, a new threshold for the ASI–Boundary-layer air Stagnation Index (BSI) is proposed, consisting of daily maximal ventilation in the atmospheric boundary layer, precipitation, and real latent instability. In the present study, the climatological features of the BSI are investigated. It shows that the spatial distribution of the BSI is similar to the ASI; that is, annual mean stagnations occur most often in the northwestern and southwestern basins, i.e., the Xinjiang and Sichuan basins (more than 180 days), and least over plateaus, i.e., the Qinghai–Tibet and Yunnan plateaus (less than 40 days). However, the seasonal cycle of the BSI is changed. Stagnation days under the new metric are observed to be maximal in winter and minimal in summer, which is positively correlated with the air pollution index (API) during 2000–2012. The correlations between the BSI and the concentration of fine particulate matter (PM2.5) during January 2013 and November to December in 2015–2017 of Beijing are also investigated. It shows that the BSI matches the day-by-day variation of PM2.5 concentration very well and is able to catch the haze episodes.

How to cite: Huang, Q., Cai, X., Wang, J., Song, Y., and Zhu, T.: Climatological study of the Boundary-layer air Stagnation Index for China and its relationship with air pollution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4454, https://doi.org/10.5194/egusphere-egu2020-4454, 2020.