In a five year field experiment we quantified the response of subalpine pasture productivity to climate change factors temperature and precipitation in interaction with increased atmospheric N-deposition.

On six southerly exposed alps in Graubünden (all at c. 2150 m a.s.l., six different plant communities) 0.25 × 0.40 m area turf monoliths were excavated. 216 monoliths were transported to the experimental Climate Change-scenario sites (CS) in Engiadina Bassa. Monoliths were reinstalled in the ground at six altitudinal levels (from 2360 to 1680 m a.s.l.). Compared to the mean temperature at the original sites the altitudinal gradient of the CS represented a temperature contrast (April – October) of -1.4 to +3.0° C. Supplemental irrigation aimed at adding up to 50% of natural precipitation to compensate for increased evapotranspiration under higher temperatures. The N-deposition treatment was equivalent to +3 and +15 kg N ha^-1 yr^-1, on top of a background deposition of c. 4 kg N ha^-1 yr^-1. Grassland yield was assessed annually as aboveground plant dry matter (>2 cm) at canopy maturity.

Yield responses to experimental treatments and annually changing weather conditions showed the limits of beneficial temperature effects at different soil moisture availabilities in this warmth limited ecosystem. The ‘comfort zone’ for this ecosystem can now be clearly defined.

We found that temperature related yield gains were possible even at the +1.8° C site. Water scarcity became a limiting factor only at +3° C warming. Both warmth and water availability individually modulated the yield by about 30% of the maximum. Analysis has not revealed an N-deposition effect on plant productivity, even in the +15 kg N ha^-1 yr^-1 treatment.

The CO₂-C balance (NEP) of subalpine pastures under climate change conditions

We quantified subalpine grassland ecosystem CO₂ flux responses to climate change factors temperature and precipitation, in interaction with increased atmospheric N-deposition in a five year field experiment. Fluxes were measured using dynamic CO₂ concentration cuvettes and parameterized to the whole five year period using light intensity, soil moisture and temperature. The NEP parameterizations will be compared to soil organic C stock measurements at the beginning and at the end of the experiment.

Results will be discussed in the light of our earlier work, that suggests increased C sequestration at low N deposition, but decreased C sequestration at high N deposition (Volk et al., Biogeosciences, 2016; Volk et al., Soil Biology and Biochemistry, 2018). At the same time, the effect of rising temperature, accompanied by reduced soil moisture, is expected to make the ecosystem a CO₂ source to the atmosphere (Volk et al., Global Change Biology, 2011), or at least to reduce potential ecosystem C gains.

Alpine environments are undergoing extensive changes in plant communities and soil properties due to an accelerated rate of climate change compared to lowland regions. Ecotone boundaries, such as treeline and glacier margin, are shifting upslope which has major implications on alpine vegetation and soil dynamics. Treeline advance may displace or out-compete alpine vegetation dependent on the suitability of recently-deglaciated terrain for growth and survival. Soil gaseous fluxes and their relationship with plant communities are less well understood in the Canadian alpine and have important repercussions on climate change globally.

I documented the current state of alpine plant community composition and soil properties along an elevational gradient, the effects of soil properties on plant species survival in recently-deglaciated terrain, and the direction, magnitude, and mechanistic drivers of methane and carbon dioxide fluxes at the soil surface in an alpine valley in the Northern Selkirk Mountains, British Columbia.

Current soil properties may be limiting treeline advance and have a strong relationship with alpine vegetation communities. The relatively slow development of soil properties may also limit the movement and establishment of herbaceous alpine vegetation into recently-deglaciated terrain, however, there is a potential for some species to survive in these areas. Soil methane uptake in the alpine environment can contribute to offset the general trend of greenhouse gas emission globally, although uptake is lower than emissions in many other ecosystem types (e.g., boreal wetlands). Climate change effects seem to reinforce methane uptake in alpine soils and could lead to a negative feedback in these areas.

Dynamics of soil methane uptake along an environmental gradient in the Columbia Mountains, Canada.

Soil gaseous fluxes are important contributors to the balance of greenhouse gases in the atmosphere. Alpine ecosystems are understudied regarding methane and carbon dioxide fluxes and the mechanisms that drive them. As climate change continues to disproportionately affect alpine regions the drivers and magnitudes of gas fluxes in these areas need to be understood to determine potential feedback effects as vegetation communities and soil properties shift. We used a portable laser analyzer to determine methane and carbon dioxide fluxes along an environmental gradient that encompassed recently-deglaciated terrain, alpine pass terrain, and an elevational slope from alpine to just above treeline. Methane uptake was highest in the alpine locations and at the middle elevational band (-2.94 and -4.86 mg CH₄ m^-2 h^-1, respectively), while no methane fluxes were found in recently-deglaciated terrain. Soil water content and vegetation coverage were the primary drivers of methane fluxes with the largest uptake occurring under low moisture and high vegetation conditions. Vegetation community changes, such as treeline advance, and soil drying to due climate change will likely enhance the methane uptake of temperate alpine areas leading to a negative feedback effect on climate change from these regions.

Future climate change scenarios predict that precipitations patterns will be modified and drought will become more frequent in Alpine grasslands, which may compromise efficient future management. To assess the reaction of Alpine grassland to drought conditions, various lysimeter experiments were performed at the long term socio-ecological research (LTSER) site ‘Stubai Valley’, Tyrol, Austria. Two types of Alpine grasslands (humid and drought adapted vegetation) were grown and subjected to varying drought conditions.

Lysimeter experiments revealed that the tested Alpine grasslands follow different water use strategies and differ in their productivity under drought conditions. Although for both grassland types productivity was strongly reduced by drought, humid adapted vegetation experienced drought more strongly. It risked hydrological failure and did not reduce transpiration until the drought was severe, resulting in lower biomass productivity and a strong decrease of soil water content. Contrastingly, drought adapted vegetation restricted faster stomatal conductance and produced more biomass using scarce water resources efficiently. Species exclusive for each vegetation type are known to differ in their irrigation preferences, what could be decisive in the water use strategy of the vegetation.

Functional groups present in both vegetation types (legumes and grasses) followed different water use strategies. Legumes showed stringent stomatal control; nevertheless their productivity decreased strongly after drought and did not recover even when rainfall conditions were restored. By contrast, grasses restricted stomatal conductance later and their productivity was barely affected and even increased when water availability was restored. They showed higher productivity rates than well irrigated vegetation. These reactions led to an increment of grasses biomass and a dramatic descent of legumes, what could have implications on the carbon and nitrogen cycle of the grassland ecosystem.

Future climate change scenarios predict an increase of the occurrence of drought periods in Alpine grasslands, which provide multiple ecosystem services such as water provisioning and grassland productivity. To assess the reaction of Alpine grassland to varying drought conditions, two grassland seed mixtures with different plant species composition (drought and humid adapted grassland), were cultivated and investigated in a garden experiment at the long term socio-ecological research (LTSER) site ‘Stubai Valley’, Tyrol, Austria. Seed mixtures were grown on standardized soils in high precision lysimeters and the stomatal conductance of the main functional groups, legumes and grasses, was measured during a drought experiment.

Results of this experiment revealed that the two Alpine grasslands follow different water use strategies and differ in their productivity under drought conditions, while in moist conditions they acted similar. Humid adapted vegetation experienced drought earlier and more strongly; it risked hydrological failure and did not reduce transpiration until the drought was severe, resulting in lower biomass productivity and a strong decrease of soil water content. Contrastingly, drought adapted vegetation restricted faster stomatal conductance and produced more biomass using scarce water resources efficiently. Differences between functional groups were also found, grasses restricted stomatal conductance when drought was severe and productivity was not affected. Contrastingly, legumes showed stringent stomatal control, nevertheless their productivity decreased strongly after drought, especially in humid adapted vegetation. Species exclusive for each vegetation type are known to differ in their irrigation preferences, what could be decisive in the water use strategy of the vegetation. Medicago sativa and Festuca arundinacea, abundant in drought adapted vegetation are considered drought resistant; while Trifolium hybridum, present in humid adapted vegetation show a preference for moderately humid soils. Hence, plant community composition could be an important factor in the response of grasslands to climate change.

Southern hemisphere mountain ecosystems are not as well represented on the global stage as northern hemisphere mountain ecosystems are. As a result, southern hemisphere mountain systems are often less well understood, and therefore often prone to assumptions for management and mitigation biased to northern perspectives. For example, the absence of a clear tree-line in these grassland-dominated systems often masks the effects of climate change compared to typical northern hemisphere systems that can monitor upward movement of trees and shrubs and correlate this to thermal changes. Also, the natural role of fire in these semi-arid and drought-prone southern systems drives a biodiversity suite that is very different in ecology and life strategy to those in northern systems. Thus, different means of measuring and monitoring change in grass-dominated southern hemisphere mountains are necessary. We use the endemic-rich Maloti-Drakensberg as a case in point to show the potential for measuring change through (1) considering the masking effects of immediate anthropogenic change (usually a more dramatic and immediate concern in real time), and (2) considering background subtle change. For the latter, we explore potential indicators such as biodiversity erosion, species composition shifts, C3-C4 grass community changes, woody species expansion, and colonisation by non-native species (invasive and naturalised). Challenges to these indicators being effective are - as mentioned - the masking effects of immediate change, but also the gradual erosion of ecosystem resilience from long periods of unsustainable use (e.g. communal rangeland degradation since the 1800s). Given the extremely high water production value of these mountains in arid and semi-arid southern Africa, the long-term resilience of such ecosytems should be very high priority for research, policy and practice.

In the global discourse, southern African mountains remain some of the most poorly considered in terms of understanding them and their 'Wicked Problems' within the framework of social-ecological systems thinking. Accordingly, growing a community of practice of high excellence is necessary to fill this gap and provide sound input into policy and practice for future mountain sustainability. Of particular concern in southern African mountains is the challenge of compromised water production landscapes from rangeland degradation, invasive species, afforestation, mining and climate change (among others).

The Afromontane Research Unit (ARU) - based on the QwaQwa Campus of the University of the Free State - seeks to become a continental leader in African mountain research. With an immediate focus on it's 'back garden' - the Maloti-Drakensberg - the ARU is driving a high intensity research portfolio; is attracting high quality students and post-grads; and forming strong partnerships with other academic players and industry in southern Africa and beyond. Research is being channelled into trans-disciplinary themes that provide input into highly relevant and complex local situations that have global implications.

The ARU has four Objectives:

1. To contribute intellectually and practically to the sustainable development discourse of the Maloti-Drakensberg as a unique social-ecological system.
2. To place the poorly studied southern African montane systems (i.e. those south of the Congo rainforest and Tanzania) onto the continental and global mountain research, policy and governance arena.
3. To facilitate the development of a mountain research ‘community of practice’ within Africa that leads African mountain research from within Africa.
4. To inform mountain hypotheses, theories & impacts of global significance from an African perspective, and thus contribute to strengthening the role of the South in the global mountain research agenda.

The ARU welcomes productive, collaborative partnerships with those seeking to understand southern African mountains as social-ecological entities, and actively encourages visits and exchanges with the ARU.

Mountain soils in alpine and nival zones are characterized by a reduced abundance of higher plants thus of a reduced input of organic matter and by overall harsh weather conditions. Even more – it is well established that average temperature has increased more distinctly in alpine regions compared to lowlands, meaning that the effect of climate change should be more pronounced in mountain systems. The vulnerability of alpine plants which in higher regions mainly form alpine meadows is well documented and climate change was shown to cause altered species composition and productivity of alpine meadows. Contrary, the effects of increasing temperature on belowground soil microorganisms remain unclear although microorganisms are not only (like plants and animals) passively influenced by climatic conditions but also actively affect them. It is especially unclear if increasing temperatures might also lead to an increased abundance and activity of soil microorganisms along an elevation gradient.

Therefore, we examined if and to which extent abundance, activities and -diversity of soil microorganisms are affected along an elevation gradient comprising alpine and nival zones. We used a gradient between 2700 m asl and 3300 m asl at Mount ’Schrankogel‘ in the Central Alps of Tyrol with a closed alpine meadow at the lowest and only sparse vegetation at the highest site. We took soil samples in triplicate every 100 m and investigated a couple of soil chemical and microbiological properties.

Microbial biomass and activities showed nonlinear sigmoidal responses to increasing altitude and decreasing temperatures. The inflection point, determined via the second derivation of the microbial response curves, exactly matched the zero degree line and so microbial activities including nutrient cycling in alpine soils should increase accompanying increasing temperatures. Noteworthy, microbial diversity was highest at the zero degree line where the thinning out of alpine meadows was mostly pronounced.

Alpine grasslands provide various ecosystem services at regional and global scales. Snow cover is integral to their functioning as it insulates the soil, and thereby protects it from very cold temperatures. This allows seasonally distinct soil microbial communities to perform belowground ecosystem functions throughout the winter. However, the annual accumulation and duration of snow cover is declining in these ecosystems due to climate change. This results in more frequent freeze-thaw cycles and earlier spring snow-melt. The consequences of this for soil microbial communities and their functioning remains uncertain. We experimentally tested how differences in snow cover, via snow addition and snow removal, affected seasonal transitions in soil microbial communities and microbial-mediated functions in alpine grassland. Our alpine grassland field site was located at Hohe Mut (2650 m.a.s.l.), near Obergurgl in the Austrian Alps. We found that snow-melt induced a rapid shift in the composition of soil microbial communities and their functioning, measured as enzyme activities involved in a range of nutrient cycles. This shift was delayed by snow addition and advanced by snow removal treatments, which was ultimately related to differences in snow-melt timing. Treatment effects were no longer detected a month after snow-melt, indicating that effects of snow-melt timing on microbial communities are transient. Nonetheless, changing snow cover clearly affected the timing of seasonal microbial community transitions and hence, potentially, the functioning of these ecosystems. Given that future climate change will likely lead to reduced snow cover and duration in alpine grasslands, the transient effects of changing snow conditions in our study are likely to become more important. Our findings imply that winter soil microbial communities and their functioning in alpine grasslands will be weakened in the future, due to climate change.

Besides fodder, milk and meat production, alpine mountain pastures (alms/alps) have been recognized as an extraordinary habitat containing high species and structural diversity. However, abandonment of alms since the 1950s due to agricultural intensification has been the quantitatively most important land use change in the alpine region. The consequence of grazing abandonment at many alms has been a decreased species diversity, a dominance of grass with increased surface flow, decreased soil water capacity and a higher risk of erosion and snow avalanches. On the other hand, climate change, occurring at a higher pace in the alpine areas compared to global average, is increasingly leading to rapid reforestation of abandoned alms.

The only way to counteract the aforementioned negative impacts on abandoned alms, and to prevent further loss of alms due to reforestation, is the revitalization of abandoned mountain pastures. However, there is a lack of knowledge how re-grazing of abandoned alms is affecting a wide range of soil functions and ecosystem services (e.g. nutrient cycles and forage value, plant and animal biodiversity, water quality and cycling, erosion control and flood prevention, greenhouse gas balance). Hence, in the frame of the SUSALPS project a transdisciplinary research team has initiated a pilot experiment of long-term alm-revitalization at Brunnenkopfalm in the Ammergebirge mountain range (South-Germany). The experiment started in 2018 after >60 years of grazing abandonment, using the traditional cattle breed Murnau-Werdenfelser. The response of a wide range of parameters to re-grazing is monitored, ranging from animal performance, societal acceptance, species and structural diversity, soil carbon storage and, nutrient dynamics, water quality, and forage value. First results on short-term re-grazing effects on plant and soil parameters gained in first alm-revitalization season 2018 will be shown.

Flowering phenology of mountain plant species is highly influenced by environmental events that determine the growing season such as snow cover, date of snowmelt, temperature and precipitation regimes as well as drought or frost events. Reactions to altered climatic conditions are species-specific. However, phenological shifts depend on which trait has been monitored and onset, peak and end of flowering might react independently.

Within the SusAlps Project we have translocated intact soil-plant communities from 6 different study sites (Bayreuth DE, 350 m a.s.l., Fendt DE, 550 m a.s.l., Graswang DE, 900 m a.s.l., Esterberg DE, 1300 m a.s.l., Stubai AU, 1850 m a.s.l. and Furka CH, 2440 m a.s.l.) spanning an climatic gradient from an alpine to a colline environment. We have monitored green cover and flowering phenology of each monolith translocated to Bayreuth during the growing season and found first differences in onset and duration of flowering depending on origin. For the coming season of 2019 we will weekly monitor a subset of origin sites to gain a better understanding of climate driving phenological processes. It is planned to present these novel results at the IMC 2019 in Innsbruck.

As a result of climate change, extreme climatic events such as drought are expected to increase in intensity and in frequency, which will have impacts on global carbon cycling. Terrestrial soils contain very large amounts of carbon, and soil respiration (Rs) is the biggest flux of CO₂ from terrestrial ecosystems to the atmosphere. Global warming is expected to enhance drought-impacts on soil respiration whereas elevated CO₂ has been suggested to enhance soil respiration and slow down the drying of soils. The combined consequences are yet unclear. Studying the vertical soil CO₂ distribution and production under drought can shed light on the mechanisms and processes underpinning soil respiration responses to drought.

Within the ClimGrass-project at AREC Raumberg-Gumpenstein, we assessed above- and belowground soil CO₂ flux- and concentration dynamics during and after an experimental drought event under ambient conditions (C0T0) and under a +3°C warming scenario with a CO₂ increase of 300ppm (C2T2). For each of the four treatments three replicated grassland plots were equipped with an automated soil respiration system to assess high-resolution Rs fluxes. Additionally we investigated soil CO₂ concentrations with a multiplexed membrane tube system installed across the soil profile at 3, 9, 18 and 36 cm soil depth.

Our results show that future (C2T2) climate increased, and that drought strongly reduced Rs fluxes compared to ambient (C0T0) climate conditions, indicating lower resistance of Rs under future climate. All drought and post-drought effects on Rs were more strongly pronounced in a future compared to a current climate, including Rs reduction during drought and CO₂ pulses after rewetting. Rewetting led to a transient overshooting of corresponding control-fluxes after the drought.

As a result of climate change, extreme climatic events such as drought are expected to increase in intensity and in frequency, which will have impacts on global carbon cycling. Terrestrial soils contain very large amounts of carbon, and soil respiration (Rs) is the biggest flux of CO₂ from terrestrial ecosystems to the atmosphere. Global warming is expected to enhance drought-impacts on soil respiration whereas elevated CO₂ has been suggested to enhance soil respiration and slow down the drying of soils. The combined consequences are yet unclear. Studying the vertical soil CO₂ distribution and production under drought can shed light on the mechanisms and processes underpinning soil respiration responses to drought.

Within the ClimGrass-project at AREC Raumberg-Gumpenstein, we assessed above- and belowground soil CO₂ flux- and concentration dynamics during and after an experimental drought event under ambient conditions (C0T0) and under a +3°C warming scenario with a CO₂ increase of 300ppm (C2T2). For each of the four treatments three replicated grassland plots were equipped with an automated soil respiration system to assess high-resolution Rs fluxes. Additionally we investigated soil CO₂ concentrations with a multiplexed membrane tube system installed across the soil profile at 3, 9, 18 and 36 cm soil depth.

Our results show that future (C2T2) climate increased, and that drought strongly reduced Rs fluxes compared to ambient (C0T0) climate conditions, indicating lower resistance of Rs under future climate. All drought and post-drought effects on Rs were more strongly pronounced in a future compared to a current climate, including Rs reduction during drought and CO₂ pulses after rewetting. Rewetting led to a transient overshooting of corresponding control-fluxes after the drought.

An in-depth analysis of soil CO₂ gradients and fluxes across the soil profile showed unexpected modifications of soil-CO₂ production and transport processes, concerning both drought and post-drought effects, especially when considering the duration of detectable drought effects.

CO₂ production in the most active layers got decreased to almost zero, with the highest activity moving down to 36cm soil depth. While soil CO₂ production in both climate scenarios recovered in rather expected timeframes, CO₂ concentration reestablishment required up to 5 months after rewetting.

Previous studies have demonstrated that microbial community resilience depends on microbial community composition. Fungal dominated communities are more resistant while bacterial dominated ones are more resilient. To riche a more mechanistic understanding of cascading effects from farming practices to ecosystem resilience, a direct assessment of microbial traits would be necessary. In this workshop, I propose to present experimental studies using community weighted traits to inform on the strategy of the microbial community members. Indeed, microbial biomass stoichiometry, ecoenzymatic ratios, mass specific extracellular enzymes activities or metatranscriptomic (mRNA sequencing) can be used as direct proxy of resource acquisition strategy. These microbial traits measures were crossed with microbial community composition (PLFA or metabarcoding), plant traits and soil abiotic properties (C, N and P pools) to better understand the drivers of microbial community traits and resilience. This approach was used in three greenhouse experiments. Two experiments used intact plant-soil cores, extracted along an intensity gradient of a mountain grasslands landscape, and exposed to simulated extreme climatic events (drought or flood or intermittent rain regimes). Another experiment, used mesocosms filled with a mountain grasslands soil and test how mineral fertilization and plant presence can modify microbial community and ecosystem resilience to drought, flood and freeze/thaw events. We have also started to use such ecoenzymatic traits in a survey project all over the French Alps along 20 altitudinal gradients to assess how soil microbial activities are related to climate, soil and plant diversity (taxonomic and functional).

With about 5 Mio ha grassland soils represent about 30% of the total agricultural area of Germany. One of the largest grassland regions in Germany, spanning > 1 Mio ha, is the grassland belt in the alpine and pre-alpine region of South-Germany. These alpine and pre-alpine grassland soils, including even larger adjacent areas in Austria, Italy, France, and Switzerland are mainly used for fodder production for dairy and beef cattle and thus are of outstanding importance for the regional economy. In addition to the economic value, these grassland ecosystems are important biodiversity conservation targets and provide important ecosystem services such as carbon (C) and nitrogen (N) storage, water retention and purification as well as recreation that serves tourism. All of these ecosystem services are affected by climate and land management changes. Impacts of climate change on alpine and pre-alpine grassland soils are most critical. This is related to i) the high sensitivity of grassland soil C and N stocks, productivity, and biodiversity to changes in temperature and rainfall, ii) the twice as high warming of (pre-) alpine regions of Central Europe compared to the global average trend, and iii) the occurrence of higher frequencies of droughts and floods.

In this contribution, we present key findings of the first phase of the interdisciplinary SUSALPS (Sustainable use of alpine and pre-alpine soils in a changing climate) project on impacts of climate changes on central grassland functions regarding biomass production, soil carbon, and N storage, turnover, and associated losses to the environment. SUSALPS aims to provide a holistic, evidence-based and process-focused understanding of the responses of key pre-alpine and alpine grassland soil functions to present day and future climate and land management changes, thereby considering specific socio-economic conditions in given regions.

Alpine regions contribute important ecosystem functions and services, and are at the same time particularly vulnerable to the ongoing climate change. In addition to the direct effects of increased temperature and changes in precipitation, indirect effects of climate-induced shifts in plant dominance can affect ecosystems and their functioning through a complex series of biotic cascades, couplings, and feedbacks. Quantifying the role of climate in mediating biotic and abiotic interactions is a challenging task, particularly when considering the magnitude of projected changes in climate in alpine regions.

We disentangle the roles of and interactions between characteristic and important alpine primary producers (graminoids, forbs, woody and non-vascular plants) and decomposer (bacteria vs. fungi) communities under climate change. In a removal experiment, we test for the the role of each primary producer in regulating biodiversity and carbon dynamics in semi-natural grasslands in southern Norway. Using natural and independent large-scale temperature and precipitation gradients in the landscape, we test for the mediating effect of climate on biotic and abiotic interactions.

We find that shifts in primary producers regulate microclimate and plant community dynamics, particularly under warmer and wetter climate conditions. Shifts in primary producer abundance in alpine grasslands will have a large impact on primary production, resulting in a shift the balance of net ecosystem exchange to increased carbon release.

High elevation ecosystems will experience increasing periods of above-average warmth and altered precipitation changes due to climate change. This causes uncertainties in predicting plant community productivity and biodiversity. Increasing temperature may increase productivity by increasing growing season length and metabolic rate or decrease productivity by causing drought stress. Competitive outcomes between species may change with altered climatic conditions causing shifts in community composition.

This study is part of the SUSALPS project and investigates the resistance of aboveground biomass and plant community composition of montane and alpine grassland ecosystems to abruptly altered temperature and precipitation conditions. Intact plantsoil communities were translocated downslope spanning an elevational gradient of 2090m in the European Alps.

We hypothesize that increasing temperature leads to i) increased aboveground biomass in the absence of precipitation deficits ii) decreased species richness and iii) shifts in plant community composition. After one year of initial exposure to their new environment, aboveground biomass changes appeared to be dependent on precipitation regimes, whereas species richness declined consistently with changed climatic conditions. No shift in community composition was found. Abrupt changes in climatic conditions can lead to rapid responses of community properties, questioning whether these high elevation communities have low initial resistance to future heat waves and droughts.

Pastures and meadows are a typical and characteristic habitat for the European Alps. They provide important economic and ecological value. Besides the economic value as production site for cattle or diary fodder, these ecosystems also provide important ecological services such as ground water protection, soil erosion control and maintenance of biodiversity. The continuous agricultural use of these regions in the past has formed and in the future will preserve these semi-natural ecosystems.

However, these ecosystems are exposed to drastic global changes, especially climate and land-use changes. Annual mean temperature is predicted to rise and this trend is expected to be most severe in high altitudes. Additional, precipitation will decrease in mountain regions especially during the growing season. Besides the change of long-term average temperature the intra- and interannual variability will increase. All of these climatic changes pressure montane ecosystems and also stakeholders by high ambiguity of their pastures seasonal economic output.

To ensure high yield quantity as well as quality we need to better understand the interplay between land-use regimes and climate change and their influence on the ecosystem services of montane grasslands. Especially the resistance and resilience of these ecosystems is going to be a key aspect in regard to the projected climatic changes.

How to adapt land-use regimes of montane grasslands with ongoing climate change

Pastures and meadows are a typical and characteristic habitat for the European Alps. They provide important economic and ecological value. Besides the economic value as production site for cattle or diary fodder, these ecosystems also provide important ecological services such as ground water protection, soil erosion control and maintenance of biodiversity. The continuous agricultural use of these regions in the past has formed and in the future will preserve these semi-natural ecosystems.

However, these ecosystems are exposed to drastic global changes, especially climate and land-use changes. Annual mean temperature is predicted to rise and this trend is expected to be most severe in high altitudes. Additional, precipitation will decrease in mountain regions especially during the growing season. Besides the change of long-term average temperature the intra- and interannual variability will increase. All of these climatic changes pressure montane ecosystems and also stakeholders by high ambiguity of their pastures seasonal economic output.

To ensure high yield quantity as well as quality we need to better understand the interplay between land-use regimes and climate change and their influence on the ecosystem services of montane grasslands. Especially the resistance and resilience of these ecosystems is going to be a key aspect in regard to the projected climatic changes.

To study the effect of climate change and differing land-use regimes intact plant-soil monoliths were translocated downslope along an elevational gradient (550 – 1350 m.a.s.l.) in the European Alps. We simulated two land-use regimes (extensive and intensive) and monitored community productivity, leaf-chemistry and biodiversity from 2017-2018.

Preliminary results so far suggest that intensive land-use regimes are less resistant to high intraannual variation.

Terrestrial ecosystems have the capacity to mitigate global warming, accounting for the reduction of one quarter of anthropogenically released CO₂. However, there is a high uncertainty about the response of land ecosystems under a warming climate regarding their carbon sink function. It has been proposed, that warming can turn terrestrial ecosystems into a carbon source by enhancing carbon loss more than carbon uptake. Investigating this response is especially crucial in northern latitudes, where warming is more pronounced and about 30% of the global soil carbon is stored. It has been suggested that increased nitrogen (N) availability, e.g. from warming or N deposition, could maintain the CO₂ sink function by stimulating gross primary productivity (GPP) in those nutrient limited ecosystems, which could potentially counteract carbon losses from respiration.

Here we studied the response of ecosystem and soil CO₂ fluxes of a subarctic grassland in Iceland to soil warming and N fertilization. The study was performed with closed dynamic chamber systems on fertilized (+50 kg N ha^-1 year^-1) and unfertilized plots placed along a geothermal warming gradient with warming levels from 1 to more than 10°C. Ecosystem and soil CO₂ fluxes increased along the warming gradient. As respiration responded more sensitively to warming than GPP, the net ecosystem uptake of CO₂ decreased with soil warming. Surprisingly, N fertilization did not affect the CO₂ fluxes on unwarmed or warmed plots. The study suggests that soil warming can turn subarctic grasslands into a carbon source, accelerating global warming by positive climate-carbon cycle feedbacks.

Carbon storage in grassland soils is regulated by combination of biotic and abiotic processes. An improved knowledge of the relationship between these stabilization mechanisms is decisive to recommend best management practices for climate change mitigation. Alpine and pre-alpine grassland soils in Bavaria represent a good example for mountainous grassland soils faced with climate change. We sampled grassland soils and recollected earthworms of the northern limestone Alps in Bavaria along an elevation gradient: 550 m a.s.l (Fendt), 900 m a.s.l (Graswang) and 1300 m a.s.l (Esterberg). We studied the distribution of soil organic carbon (SOC) according to aggregate size classes: large-macroaggregates (> 2000 µm), small-macroaggregates (250-2000 µm), microaggregates (63-250 µm), silt plus clay particles (<63 µm) and bulk soil. In addition, we analyzed the different ecological niche groups of earthworms and determined their biomass. Our results showed higher SOC contents and altered distribution of water-stable aggregates in high elevation sites compared to lower elevations. SOC and N stocks of bulk soils showed the same trend than OC contents in aggregates, with higher values at high elevation sites. A principal component analysis revealed that SOC and N together with biomass of adult epigeic and adult endogeic earthworms seem to play an important role in macro and micro aggregate formation, whereas magnesium carbonate and clay content seem to play an important role in stabilizing silt+plus clay fraction. These results will improve our understanding of the effects of climate change on soil structure and on the sensitivity of different biotic and abiotic mechanisms of C stabilization in mountainous grassland soils.

Extreme events, such as drought, can substantially alter the biogeochemical cycles of carbon (C) and nutrients. Soil microorganisms play a key role in C and nutrient cycling. While considerable progress has been made in understanding the effects of singular drought events on soil microbial community structure and processes, we still lack information on whether recurrent drought events will exhibit legacy effects on microbial responses to a subsequent drought event. The aim of this experiment was to evaluate whether the microbial responses to a drought event is altered by a previous history of drought events.

For this we set up an experiment in a subalpine grassland, including a control versus plots subject to drought either for the first time or for the 10^th consecutive year. We assessed the microbial community stoichiometry and composition (PLFA analysis and 16S/ITS amplicon sequencing), analyzed potential enzymatic activity of enzymes involved in the cycling of C, nitrogen, phosphorous and sulphur. We constructed a multifunctionality index of the system (including plant primary production and multiple soil functions) to represent the ecosystem ability to maintain multiple functions and services under re-current drought events.

Our results show a divergent response of the re-current and single drought events. The microbial community of the single drought treatment did not show strong changes, neither in composition nor in nutrient acquisition strategy, but had altered biomass stoichiometry and multifunctional index. In contrast, previous drought history strongly changed the microbial community composition, potential enzymatic activities and the nutrient acquisition strategy, while microbial stoichiometry and multifunctional index values were similar to non-drought controls.

From our experiment we conclude that a history of drought events over multiple consecutive years can cause microbial adaptation and the formation of a divergent microbial community with different nutrient acquisition strategies and able to maintain ecosystem functionality under drought stress.

Climate and land-use change have the potential to affect ecosystem structure and functioning, consequently altering ecosystem services, especially in alpine ecosystems that are ecologically sensitive. This study aims to: (i) monitor the inter-annual variability of LAI and biomass production in a subalpine grassland, focusing on different responses of grasses and forbs; (ii) describe structural changes of plant community after nine years of grazing exclusion; (iii) investigate the interaction between ecosystem structure and responses to climate change, focusing on temporal stability.

The study area is located on the western Italian Alps and is occupied by a subalpine grassland dominated by Nardus stricta. Three different plots (600 m²) were identified within the area, two inside a fence excluding grazing, and the third outside and still occasionally grazed. Biomass samples were collected every ~10 days and then sorted in grasses and forbs prior to measure LAI and dry weight. Finally, two vegetation surveys were carried out in 2009 and 2017 following the point transect method.

The observed high variability in snow cover duration, precipitation, and air temperature among years led to a high variability in LAI and biomass production, which were negatively affected by the heat waves occurred in 2015 and 2017. Differently to grasses, forb biomass was not affected by drought and showed even higher values. Moreover, the three plots showed different levels of temporal stability during the heat waves.

The high variability among different seasons showed that climatic drivers may cause changes of the growing season pattern even in a short period. Since forbs and grasses responded differently to climatic conditions, we suggest that the different stability of the three plots depended on the dominance of different functional types. In this framework, land-use change, affecting the structure of subalpine grasslands, may have a role in the ecosystem responses to climate change.

Plant species capable of growing at different altitudes are good models to study plant acclimation and adaptation to different environments. Alpine regions are characterized by strongly fluctuating environmental factors including freezing temperatures in winter and summer, in high alpine habitats especially. Therefore, freezing resistance is a decisive factor for plant survival. Arabidopsis arenosa (L.) Lawalrée, a close relative of A. thaliana (L.) Heynh., covers altitudinal gradients from lowlands up to over 2000m a.s.l. However, it is still unknown if freezing resistance in different ecotypes of A. arenosa reflects adaptation to the environment or if can be gained by acclimation. We conducted a reciprocal transplantation experiment by planting seedlings of eight pairs of geographically close alpine and foothill populations from three different geographical regions, the Eastern European Alps, the Făgăraș Mountains (Southern Carpathians) and the Tatra Mountains to two common gardens situated at low (foothill) and high (alpine) elevations. Populations from the Tatras were diploid or tetraploid, and all others were tetraploid. Differential thermal analysis (DTA) and infrared differential thermal analysis (IDTA) in conjunction with assessing lethal temperatures (LT₅₀) revealed differences in freezing resistance, ice nucleation and ice propagation patterns. Within populations grown in the foothill and alpine common gardens, LT₅₀ varied between -0.7±0.2 and -11.4±2.2°C, respectively. In the alpine common garden, alpine ecotypes had a significantly lower freezing resistance compared to their foothill counterparts. Furthermore, geographic origin was a significant factor for freezing resistance. Populations from the Tatra Mountains survived lowest freezing temperatures (9.2±3.0°C); their freezing resistance was also affected by ploidy level in both common gardens. In conclusion, the differences between alpine or foothill populations were largely maintained when they were grown in the two common gardens. This could indicate that this functional trait is already manifested as a determined adaptation.

In assessing alpine vegetation responses to climatic change, it can be challenging to ingerate both a warmer climate and new species- and soil biotic interactions all at once. Using whole-community transplants down elevational gradients to sites with a climate matching future predictions for that region is a greatly informative method. This allows assessment of the net effects of climate change, including both direct climate responses and effects of new species interactions, on the community structure and development. At the same time, variation in geography and other environmental variables can be controlled for. Such transplant studies have been performed in numerous mountain locations around the world, focusing on the effects of climatic warming and new species interactions.

The TransPlant Network aims to further the insights of such experiments by taking a meta-analysis approach. Combining data from our elaborate network of existing transplant studies worldwide allows us to relate general patterns of colonization and extinction to functional traits of the component species, soil properties, and local climatic variables. Moreover, trait-based analyses will allow us to predict ecological processes and responses across species, systems, and spatial scales. This will greatly improve our understanding of climate change impacts on mountain vegetation, uncover underlying mechanisms, and demonstrate how these vary with ecological and environmental settings on a global scale.

TransPlant already has an extensive network of collaborators and sites (including the Mountain Invasion Network MIREN, plant functional trait courses TraitTrain, and the Norwegian projects SeedClim and INCLINE), spanning a wide range in the northern hemisphere in north America, Europe and Asia. However, we would be very happy to invite more gradients into our network, so feel free to contact us!