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Silvopastoral systems are highly productive and combine long-term wood production with annual provision of forage for livestock. In the Swiss Jura Mountains these systems are a key component of the landscape. As in other cold biomes, climate change can potentially accelerate landscape change within these historically sustainable systems. In order to anticipate the evolution of subalpine wooded pasture ecosystems under future climate and land-use changes, this project focused on the interplay between soil, vegetation and climate. It was aimed at providing experimental evidence for chief ecosystem processes, with emphasis on the quality of the ecosystem services provided. The main interest was placed on vegetation turf resistance to climate change along an unwooded – sparsely wooded - densely wooded pasture gradient (land-use intensity), where plant productivity, diversity and succession along with rates of carbon cycling and microbial activity provided measures of ecosystem functioning at both plot and landscape level. Experimental transplantation of monolith soil turfs to lower altitudes allowed to simulate soil warming and reduced annual precipitation. In order to simulate a year-round warmer and drier climate the natural climate variation along an altitudinal gradient was used as a proxy. The aim was to simulate realistic climate change scenarios for the second half of the 21st century predicted by the IPCC report and downscaled for Switzerland providing regionalized interpolated projections integrating therein trends for temperature increase and precipitation decrease. By using permanent meteorological stations within the network of the Federal Office of Meteorology and Climatology (MeteoSwiss), we obtained high resolution regional data on the variation of mean annual temperature (MAT) and mean annual precipitation (MAP) in relation to altitude in the Swiss Jura Mountains. We observed a general increase of +0.5 K in MAT and a decrease of -20 % MAP for each 100 m decrease in altitude along the SE slope of the Swiss Jura Mountains. These relationships served for the selection of the transplantation sites such that in comparison to a control site at 1350 m a.s.l. (Combe des Amburnex, N 46°54’, E 6°23’) a +2 K MAT and -20 % MAP was achieved at 1010 m a.s.l. (Saint-George, N 46°52’, E 6°26’), a +4 K MAT and -40 % MAP at 570 m a.s.l., (Arboretum d’Aubonne, N 46°51’, E 6°37’), and a +5 K MAT and -50 % MAP at 395 m a.s.l. (Les Bois Chamblard, N 46°47’, E 6°41’). The two stations at 1010 m a.s.l. and 570 m a.s.l. corresponded to the IPCC scenario A1B for a moderate increase in greenhouse gas emissions and to scenario A2 for a high increase in greenhouse gas emissions, respectively. The station at 395 m a.s.l. was chosen to represent an extreme scenario with climate variables lying at the positive tail distribution of model predictions under the A2 scenario. Soil cores were assembled into rectangular PVC boxes of 60  80 cm2 size and of 35 cm height. All mesocosms were dug down to surface level into previously prepared trenches in the ground thus preventing lateral heat exchange with the atmosphere. Since at each site the mesocosms were placed in a common garden with no light interception, mesocosms with turfs from the two wooded pastures were shaded from direct sun light to simulate the natural light conditions in the corresponding habitats. Each mesocosm was equipped with a drainage system and was connected to a water tank thus representing a zero potential lysimeter collecting soil solution and precipitation/snowmelt runoff. ECH2O EC-TM sensor probes coupled to Em50 data-loggers (Decagon Devices, Inc., USA) recorded soil temperature and volumetric water content in each mesocosm at the top-soil (0 to -3 cm) every minute and data were averaged over one hour intervals. Climate parameters at each transplantation site were monitored continuously throughout the experiment by means of automated weather stations (Sensor Scope Sàrl, Switzerland), measuring rain precipitation (non-heated tipping bucket gauges) and air temperature and humidity 2 m above the ground surface at one minute intervals. A list of above- and belowground variables were measured to assess the resilience of biogeochemical processes, plant productivity, tree regeneration, and carbon sequestration for each respective land-use practice. Furthermore, the experimental data were used to improve on (parameterization) the existing spatially explicit, dynamic model WoodPaM and refine the modelʼs climatic and land-use variables so that different scenarios of climate change and land use change could be simulated. Natural and management induced disturbance patterns were incorporated into the model. The data have been made available within the project CCES Mounted. The climate stations Sensorscope are still in use within the project CLIMARBRE (Wald und Klimawandel, WSL/BAFU). References 1. Puissant, J., Cécillon, L., Mills, R.T.E., Robroek, B.J.M. Gavazov, K., De Danieli, S., Spiegelberger, T., Buttler, A., Brun, J.J. 2015. Seasonal influence of climate manipulation on microbial community structure and function in mountain soils. Soil Biology and Biochemistry 80: 296–305. 2. Mills, R., K. Gavazov, T. Spiegelberger, D. Johnson and A. Buttler 2014. Diminished soil functions occur under simulated climate change in a sup-alpine pasture, but heterotrophic temperature sensitivity indicates microbial resilience. Science of the Total Environment, vol. 473–474(0): 465-472. 3. Gavazov, K., Spiegelberger, T. and Buttler, A. 2014. Transplantation of subalpine wood-pasture turfs along a natural climatic gradient reveals lower resistance of unwooded pastures to climate change compared to wooded ones. Oecologia (174) : 1425-1435. 4. Peringer A., Siehoff S., Chételat J., Spiegelberger T., Buttler A. & Gillet F. 2013. Past and future landscape dynamics in pasture-woodlands of the Swiss Jura Mountains under climate change. Ecology and Society, 18, 3: 11. DOI: 10.5751/ES-05600-180311. [online] URL: http://www.ecologyandsociety.org/vol18/iss3/art11/ 5. Gavazov, K. S., A. Peringer, A. Buttler, F. Gillet and T. Spiegelberger. 2013. Dynamics of Forage Production in Pasture-woodlands of the Swiss Jura Mountains under Projected Climate Change Scenarios. Ecology and Society 18 (1): 38. [online] URL: http://www.ecologyandsociety.org/vol18/iss1/art38/

AbstractClimate change can alter peatland plant community composition by promoting the growth of vascular plants. How such vegetation change affects peatland carbon dynamics remains, however, unclear. In order to assess the effect of vegetation change on carbon uptake and release, we performed a vascular plant‐removal experiment in two Sphagnum‐dominated peatlands that represent contrasting stages of natural vegetation succession along a climatic gradient. Periodic measurements of net ecosystem CO2 exchange revealed that vascular plants play a crucial role in assuring the potential for net carbon uptake, particularly with a warmer climate. The presence of vascular plants, however, also increased ecosystem respiration, and by using the seasonal variation of respired CO2 radiocarbon (bomb‐14C) signature we demonstrate an enhanced heterotrophic decomposition of peat carbon due to rhizosphere priming. The observed rhizosphere priming of peat carbon decomposition was matched by more advanced humification of dissolved organic matter, which remained apparent beyond the plant growing season. Our results underline the relevance of rhizosphere priming in peatlands, especially when assessing the future carbon sink function of peatlands undergoing a shift in vegetation community composition in association with climate change.

Peatlands are important sinks of atmospheric carbon (C) that, in response to climate warming, are undergoing dynamic vegetation succession. Here we examined the hypothesis that the uptake of nutrients by different plant growth forms (PGFs) is one key mechanism driving changes in species abundance in peatlands. Along an altitude gradient representing a natural climate experiment, we compared the variability of the stable C isotope composition (δ(13)C) and stable nitrogen (N) isotope composition (δ(15)N) in current-year leaves of two major PGFs, i.e. ericoids and graminoids. The climate gradient was associated with a gradient of vascular plant cover, which was parallelled by different concentrations of organic and inorganic N as well as the fungal/bacterial ratio in peat. In both PGFs the (13)C natural abundance showed a marginal spatial decrease with altitude and a temporal decrease with progression of the growing season. Our data highlight a primary physical control of foliar δ(13)C signature, which is independent from the PGFs. Natural abundance of foliar (15)N did not show any seasonal pattern and only in the ericoids showed depletion at lower elevation. This decreasing δ(15)N pattern was primarily controlled by the higher relative availability of organic versus inorganic N and, only for the ericoids, by an increased proportion of fungi to bacteria in soil. Our space-for-time approach demonstrates that a change in abundance of PGFs is associated with a different strategy of nutrient acquisition (i.e. transfer via mycorrhizal symbiosis versus direct fine-root uptake), which could likely promote observed and predicted dwarf shrub expansion under climate change.

Abstract Mountain ecosystems are particularly threatened by ongoing climate change and the species composition of high elevation grasslands is already changing. An open research question is how these ecosystems will adapt to changes in their key environmental constraints. The responses of wooded pastures to experimental climate forcing were analysed in a transplantation experiment conducted downslope, along an elevational temperature and precipitation gradient on the lee side of Jura Mountains, Switzerland (up to +4.17°C and −35% precipitation). To improve mechanistic understanding of biodiversity and biomass decreases in response to transplantation, changes in functional traits within foliage and roots of one ubiquitous (Taraxacum officinale) and one montane (Alchemilla monticola) perennial forb species were investigated. In consequence of transplantation, the two studied species raised their temperature optimum for CO2 assimilation and net photosynthesis yield from 20 to 30°C. During cool periods, the highest rates of leaf gas exchanges were measured at the lower recipient sites. However, an opposite trend was observed during a spring drought and summer warm spell. Regarding the more integrative morpho‐anatomical traits, Alchemilla primarily acclimated to warmer temperatures at the recipient sites with increased leaf and foliage rosette size. Missing xeromorphic and/or hydraulic adjustments in foliage and roots, its susceptibility to higher vapour pressure deficits and lower soil moisture availability was thus enhanced. Taraxacum showed adjustments to both warmer temperature and lower moisture availability, including reduced leaf size, lower hydraulic diameter of xylem vessels and theoretical specific hydraulic conductivity. The anticipated shift in the environmental conditions at high elevation, with reduced coldness limitation but increasingly constraining water economy, could thus become particularly demanding for montane species of wooded pastures. It may favour perennials with large phenotypic plasticity but leads to maladjustments and loss of the species which are more specifically adapted to montane conditions. Read the free Plain Language Summary for this article on the Journal blog.

Warming-induced increases in microbial CO2 release in northern tundra may positively feedback to climate change. However, shifts in microbial extracellular enzyme activities (EEAs) may alter the impacts of warming over the longer term. We investigated the in situ effects of 3 years of winter warming in combination with the in vitro effects of a rapid warming (6 days) on microbial CO2 release and EEAs in a subarctic tundra heath after snowmelt in spring. Winter warming did not change microbial CO2 release at ambient (10 °C) or at rapidly increased temperatures, i.e., a warm spell (18 °C) but induced changes (P < 0.1) in the Q10 of microbial respiration and an oxidative EEA. Thus, although warmer winters may induce legacy effects in microbial temperature acclimation, we found no evidence for changes in potential carbon mineralization after spring thaw.

As global temperatures continue to rise, a key uncertainty of climate projections is the microbial decomposition of vast organic carbon stocks in thawing permafrost soils. Decomposition rates can accelerate up to fourfold in the presence of plant roots, and this mechanism—termed the rhizosphere priming effect—may be especially relevant to thawing permafrost soils as rising temperatures also stimulate plant productivity in the Arctic. However, priming is currently not explicitly included in any model projections of future carbon losses from the permafrost area. Here, we combine high-resolution spatial and depth-resolved datasets of key plant and permafrost properties with empirical relationships of priming effects from living plants on microbial respiration. We show that rhizosphere priming amplifies overall soil respiration in permafrost-affected ecosystems by ~12%, which translates to a priming-induced absolute loss of ~40 Pg soil carbon from the northern permafrost area by 2100. Our findings highlight the need to include fine-scale ecological interactions in order to accurately predict large-scale greenhouse gas emissions, and suggest even tighter restrictions on the estimated 200 Pg anthropogenic carbon emission budget to keep global warming below 1.5 °C.

Microbial communities drive soil organic matter (SOM) decomposition through the production of a variety of extracellular enzymes. Climate change impact on soil microbial communities and soil enzymatic activities can therefore strongly affect SOM turnover, and thereby determine the fate of ecosystems and their role as carbon sinks or sources. To simulate projected impacts of climate change on Swiss Jura subalpine grassland soils, an altitudinal soil transplantation experiment was set up in October 2009. On the fourth year of this experiment, we measured microbial biomass (MB), microbial community structure (MCS), and soil extracellular enzymatic activities (EEA) of nine hydrolytic and oxidative extracellular enzymes in the transplanted soils on a seasonal basis. We found a strong sampling date effect and a smaller but significant effect of the climate manipulation (soil transplantation) on EEA. Overall EEA was higher in winter and spring but enzymes linked to N and P cycles showed higher potential activities in autumn, suggesting that other factors than soil microclimate controlled their pool size, such as substrate availability. The climate warming manipulation decreased EEA in most cases, with oxidative enzymes more concerned than hydrolytic enzymes. In contrast to EEA, soil MB was more affected by the climate manipulation than by the seasons. Transplanting soils to lower altitudes caused a significant decrease in soil MB, but did not affect soil MCS. Conversely, a clear shift in soil MCS was observed between winter and summer. Mass-specific soil EEA (EEA normalized by MB) showed a systematic seasonal trend, with a higher ratio in winter than in summer, suggesting that the seasonal shift in MCS is accompanied by a change in their activities. Surprisingly, we observed a significant decrease in soil organic carbon (SOC) concentration after four years of soil transplantation, as compared to the control site, which could not be linked to any microbial data. We conclude that medium term (four years) warming and decreased precipitation strongly affected MB and EEA but not MCS in subalpine grassland soils, and that those shifts cannot be readily linked to the dynamics of soil carbon concentration under climate change. (C) 2014 Elsevier Ltd. All rights reserved.