Browsing by Subject "ELEVATED CO2"

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  • Fernandez-Martinez, M.; Vicca, S.; Janssens, I. A.; Ciais, P.; Obersteiner, M.; Bartrons, M.; Sardans, J.; Verger, A.; Canadell, J. G.; Chevallier, F.; Wang, X.; Bernhofer, C.; Curtis, P. S.; Gianelle, D.; Gruewald, T.; Heinesch, B.; Ibrom, A.; Knohl, A.; Laurila, T.; Law, B. E.; Limousin, J. M.; Longdoz, B.; Loustau, D.; Mammarella, I.; Matteucci, G.; Monson, R. K.; Montagnani, L.; Moors, E. J.; Munger, J. W.; Papale, D.; Piao, S. L.; Penuelas, J. (2017)
    Concentrations of atmospheric carbon dioxide (CO2) have continued to increase whereas atmospheric deposition of sulphur and nitrogen has declined in Europe and the USA during recent decades. Using time series of flux observations from 23 forests distributed throughout Europe and the USA, and generalised mixed models, we found that forest-level net ecosystem production and gross primary production have increased by 1% annually from 1995 to 2011. Statistical models indicated that increasing atmospheric CO2 was the most important factor driving the increasing strength of carbon sinks in these forests. We also found that the reduction of sulphur deposition in Europe and the USA lead to higher recovery in ecosystem respiration than in gross primary production, thus limiting the increase of carbon sequestration. By contrast, trends in climate and nitrogen deposition did not significantly contribute to changing carbon fluxes during the studied period. Our findings support the hypothesis of a general CO2-fertilization effect on vegetation growth and suggest that, so far unknown, sulphur deposition plays a significant role in the carbon balance of forests in industrialized regions. Our results show the need to include the effects of changing atmospheric composition, beyond CO2, to assess future dynamics of carbon-climate feedbacks not currently considered in earth system/climate modelling.
  • Lischka, Silke; Bach, Lennart T.; Schulz, Kai-Georg; Riebesell, Ulf (2017)
    Community approaches to investigating ocean acidification (OA) effects suggest a high tolerance of micro-and mesozooplankton to carbonate chemistry changes expected to occur within this century. Plankton communities in the coastal areas of the Baltic Sea frequently experience pH variations partly exceeding projections for the near future both on a diurnal and seasonal basis. We conducted a large-scale mesocosm CO2 enrichment experiment (similar to 55m(3)) enclosing the natural plankton community in Tvarminne Storfjarden for 8 weeks during June-August 2012 and studied community and species-taxon response of ciliates and mesozooplankton to CO2 elevations expected for this century. In addition to the response to fCO(2), we also considered temperature and chlorophyll a variations in our analyses. Shannon diversity of ciliates significantly decreased with fCO(2) and temperature with a greater dominance of smaller species. The mixotrophic Myrionecta rubra seemed to indirectly and directly benefit from higher CO2 concentrations in the post-bloom phase through increased occurrence of picoeukaryotes (most likely Cryptophytes) and Dinophyta at higher CO2 levels. With respect to mesozooplankton, we did not detect significant effects for either total abundance or for Shannon diversity. The cladocera Bosmina sp. occurred at distinctly higher abundance for a short time period during the second half of the experiment in three of the CO2-enriched mesocosms except for the highest CO2 level. The ratio of Bosmina sp. with empty to embryo-or resting-eggbearing brood chambers, however, was significantly affected by CO2, temperature, and chlorophyll a. An indirect CO2 effect via increased food availability (Cyanobacteria) stimulating Bosmina sp. reproduction cannot be ruled out. Although increased regenerated primary production diminishes trophic transfer in general, the presence of organisms able to graze on bacteria such as cladocerans may positively impact organic matter transfer to higher trophic levels. Thus, under increasing OA in cladoceran-dominated mesozooplankton communities, the importance of the microbial loop in the pelagic zone may be temporarily enhanced and carbon transfer to higher trophic levels may be stimulated.
  • Walker, Anthony P.; De Kauwe, Martin G.; Medlyn, Belinda E.; Zaehle, Soeke; Iversen, Colleen M.; Asao, Shinichi; Guenet, Bertrand; Harper, Anna; Hickler, Thomas; Hungate, Bruce A.; Jain, Atul K.; Luo, Yiqi; Lu, Xingjie; Lu, Meng; Luus, Kristina; Megonigal, J. Patrick; Oren, Ram; Ryan, Edmund; Shu, Shijie; Talhelm, Alan; Wang, Ying-Ping; Warren, Jeffrey M.; Werner, Christian; Xia, Jianyang; Yang, Bai; Zak, Donald R.; Norby, Richard J. (2019)
    Increasing atmospheric CO2 stimulates photosynthesis which can increase net primary production (NPP), but at longer timescales may not necessarily increase plant biomass. Here we analyse the four decade-long CO2-enrichment experiments in woody ecosystems that measured total NPP and biomass. CO2 enrichment increased biomass increment by 1.05 +/- 0.26 kg C m(-2) over a full decade, a 29.1 +/- 11.7% stimulation of biomass gain in these early-secondary-succession temperate ecosystems. This response is predictable by combining the CO2 response of NPP (0.16 +/- 0.03 kg C m(-2) y(-1)) and the CO2-independent, linear slope between biomass increment and cumulative NPP (0.55 +/- 0.17). An ensemble of terrestrial ecosystem models fail to predict both terms correctly. Allocation to wood was a driver of across-site, and across-model, response variability and together with CO2-independence of biomass retention highlights the value of understanding drivers of wood allocation under ambient conditions to correctly interpret and predict CO2 responses.
  • Durand, Maxime; Murchie, Erik H.; Lindfors, Anders; Urban, Otmar; Aphalo, Pedro J.; Robson, T. Matthew (2021)
    The sunlight received by plants is affected by cloudiness and pollution. Future changes in cloud cover will differ among regions, while aerosol concentrations are expected to continue increasing globally as a result of wildfires, fossil fuel combustion, and industrial pollution. Clouds and aerosols increase the diffuse fraction and modify the spectral composition of incident solar radiation, and both will affect photosynthesis and terrestrial ecosystem productivity. Thus, an assessment of how canopy and leaf-level processes respond to these changes is needed as part of accurately forecasting future global carbon assimilation. To review these processes and their implications: first, we discuss the physical basis of the effect of clouds and aerosols on solar radiation as it penetrates the atmosphere; second, we consider how direct and diffuse radiation are absorbed and transmitted by plant canopies and their leaves; and finally, we assess the consequences for photosynthesis at the canopy and ecosystem levels. Photobiology will be affected at the atmospheric level by a shift in spectral composition toward shorter or longer wavelengths under clouds or aerosols, respectively, due to different scattering. Changes in the microclimate and spectral composition of radiation due to an enhanced diffuse fraction also depend on the acclimation of canopy architectural and physiological traits, such as leaf area index, orientation, and clumping. Together with an enhancement of light-use efficiency, this makes the effect of diffuse solar radiation on canopy photosynthesis a multilayered phenomenon, requiring experimental testing to capture those complex interactions that will determine whether it produces the persistent enhancement in carbon assimilation that land-surface models currently predict.
  • Launiainen, Samuli; Katul, Gabriel G.; Leppä, Kersti; Kolari, Pasi; Aslan, Toprak; Grönholm, Tiia; Korhonen, Lauri; Mammarella, Ivan; Vesala, Timo (2022)
    The terrestrial net ecosystem productivity (NEP) has increased during the past three decades, but the mechanisms responsible are still unclear. We analyzed 17 years (2001-2017) of eddy-covariance measurements of NEP, evapotranspiration (ET) and light and water use efficiency from a boreal coniferous forest in Southern Finland for trends and inter-annual variability (IAV). The forest was a mean annual carbon sink (252 [+/- 42] gC m-2a-1), and NEP increased at rate +6.4-7.0 gC m-2a-1 (or ca. +2.5% a-1) during the period. This was attributed to the increasing gross-primary productivity GPP and occurred without detectable change in ET. The start of annual carbon uptake period was advanced by 0.7 d a-1, and increase in GPP and NEP outside the main growing season contributed ca. one-third and one-fourth of the annual trend, respectively. Meteorological factors were responsible for the IAV of fluxes but did not explain the long-term trends. The growing season GPP trend was strongest in ample light during the peak growing season. Using a multi-layer ecosystem model, we showed that direct CO2 fertilization effect diminishes when moving from leaf to ecosystem, and only 30-40% of the observed ecosystem GPP increase could be attributed to CO2. The increasing trend in leaf-area index (LAI), stimulated by forest thinning in 2002, was the main driver of the enhanced GPP and NEP of the mid-rotation managed forest. It also compensated for the decrease of mean leaf stomatal conductance with increasing CO2 and LAI, explaining the apparent proportionality between observed GPP and CO2 trends. The results emphasize that attributing trends to their physical and physiological drivers is challenged by strong IAV, and uncertainty of LAI and species composition changes due to the dynamic flux footprint. The results enlighten the underlying mechanisms responsible for the increasing terrestrial carbon uptake in the boreal zone.
  • Bermúdez, Rafael; Winder, Monika; Stuhr, Annegret; Almén, Anna-Karin; Engström-Öst, Jonna; Riebesell, Ulf (2016)
    Increasing atmospheric carbon dioxide (CO2) is changing seawater chemistry towards reduced pH, which affects various properties of marine organisms. Coastal and brackish water communities are expected to be less affected by ocean acidification (OA) as these communities are typically adapted to high fluctuations in CO2 and pH. Here we investigate the response of a coastal brackish water plankton community to increasing CO2 levels as projected for the coming decades and the end of this century in terms of community and biochemical fatty acid (FA) composition. A Baltic Sea plankton community was enclosed in a set of offshore mesocosms and subjected to a CO2 gradient ranging from natural concentrations (similar to 347 mu atm fCO(2)) up to values projected for the year 2100 (similar to 1333 mu atm fCO(2)). We show that the phytoplankton community composition was resilient to CO2 and did not diverge between the treatments. Seston FA composition was influenced by community composition, which in turn was driven by silicate and phosphate limitation in the mesocosms and showed no difference between the CO2 treatments. These results suggest that CO2 effects are dampened in coastal communities that already experience high natural fluctuations in pCO(2). Although this coastal plankton community was tolerant of high pCO(2) levels, hypoxia and CO2 uptake by the sea can aggravate acidification and may lead to pH changes outside the currently experienced range for coastal organisms.
  • Nausch, Monika; Bach, Lennart Thomas; Czerny, Jan; Goldstein, Josephine; Grossart, Hans-Peter; Hellemann, Dana; Hornick, Thomas; Achterberg, Eric Pieter; Schulz, Kai-Georg; Riebesell, Ulf (2016)
    Studies investigating the effect of increasing CO2 levels on the phosphorus cycle in natural waters are lacking although phosphorus often controls phytoplankton development in many aquatic systems. The aim of our study was to analyse effects of elevated CO2 levels on phosphorus pool sizes and uptake. The phosphorus dynamic was followed in a CO2-manipulation mesocosm experiment in the Storfjarden (western Gulf of Finland, Baltic Sea) in summer 2012 and was also studied in the surrounding fjord water. In all mesocosms as well as in surface waters of Storfjarden, dissolved organic phosphorus (DOP) concentrations of 0.26aEuro-+/- aEuro-0.03 and 0.23aEuro-+/- aEuro-0.04aEuro-A mu molaEuro-L-1, respectively, formed the main fraction of the total P-pool (TP), whereas phosphate (PO4) constituted the lowest fraction with mean concentration of 0.15aEuro-A +/- aEuro-0.02 in the mesocosms and 0.17aEuro-A +/- aEuro-0.07aEuro-A mu molaEuro-L-1 in the fjord. Transformation of PO4 into DOP appeared to be the main pathway of PO4 turnover. About 82aEuro-% of PO4 was converted into DOP whereby only 18aEuro-% of PO4 was transformed into particulate phosphorus (PP). PO4 uptake rates measured in the mesocosms ranged between 0.6 and 3.9aEuro-nmolaEuro-L(-1)aEuro-h(-1). About 86aEuro-% of them was realized by the size fraction <aEuro-3aEuro-A mu m. Adenosine triphosphate (ATP) uptake revealed that additional P was supplied from organic compounds accounting for 25-27aEuro-% of P provided by PO4 only. CO2 additions did not cause significant changes in phosphorus (P) pool sizes, DOP composition, and uptake of PO4 and ATP when the whole study period was taken into account. However, significant short-term effects were observed for PO4 and PP pool sizes in CO2 treatments > aEuro-1000aEuro-A mu atm during periods when phytoplankton biomass increased. In addition, we found significant relationships (e.g., between PP and Chl a) in the untreated mesocosms which were not observed under high fCO(2) conditions. Consequently, it can be hypothesized that the relationship between PP formation and phytoplankton growth changed with CO2 elevation. It can be deduced from the results, that visible effects of CO2 on P pools are coupled to phytoplankton growth when the transformation of PO4 into POP was stimulated. The transformation of PO4 into DOP on the other hand does not seem to be affected. Additionally, there were some indications that cellular mechanisms of P regulation might be modified under CO2 elevation changing the relationship between cellular constituents.
  • Spilling, Kristian; Schulz, Kai G.; Paul, Allanah J.; Boxhammer, Tim; Achterberg, Eric P.; Hornick, Thomas; Lischka, Silke; Stuhr, Annegret; Bermudez, Rafael; Czerny, Jan; Crawfurd, Kate; Brussaard, Corina P. D.; Grossart, Hans-Peter; Riebesell, Ulf (2016)
    About a quarter of anthropogenic CO2 emissions are currently taken up by the oceans, decreasing seawater pH. We performed a mesocosm experiment in the Baltic Sea in order to investigate the consequences of increasing CO2 levels on pelagic carbon fluxes. A gradient of different CO2 scenarios, ranging from ambient (similar to 370 mu atm) to high (similar to 1200 mu atm), were set up in mesocosm bags (similar to 55m(3)). We determined standing stocks and temporal changes of total particulate carbon (TPC), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and particulate organic carbon (POC) of specific plankton groups. We also measured carbon flux via CO2 exchange with the atmosphere and sedimentation (export), and biological rate measurements of primary production, bacterial production, and total respiration. The experiment lasted for 44 days and was divided into three different phases (I: t0-t16; II: t17-t30; III: t31-t43). Pools of TPC, DOC, and DIC were approximately 420, 7200, and 25 200 mmol Cm-2 at the start of the experiment, and the initial CO2 additions increased the DIC pool by similar to 7% in the highest CO2 treatment. Overall, there was a decrease in TPC and increase of DOC over the course of the experiment. The decrease in TPC was lower, and increase in DOC higher, in treatments with added CO2. During phase I the estimated gross primary production (GPP) was similar to 100 mmol C m(-2) day(-1), from which 75-95% was respired, similar to 1% ended up in the TPC (including export), and 5-25% was added to the DOC pool. During phase II, the respiration loss increased to similar to 100% of GPP at the ambient CO2 concentration, whereas respiration was lower (85-95% of GPP) in the highest CO2 treatment. Bacterial production was similar to 30% lower, on average, at the highest CO2 concentration than in the controls during phases II and III. This resulted in a higher accumulation of DOC and lower reduction in the TPC pool in the elevated CO2 treatments at the end of phase II extending throughout phase III. The "extra" organic carbon at high CO2 remained fixed in an increasing biomass of small-sized plankton and in the DOC pool, and did not transfer into large, sinking aggregates. Our results revealed a clear effect of increasing CO2 on the carbon budget and mineralization, in particular under nutrient limited conditions. Lower carbon loss processes (respiration and bacterial remineralization) at elevated CO2 levels resulted in higher TPC and DOC pools than ambient CO2 concentration. These results highlight the importance of addressing not only net changes in carbon standing stocks but also carbon fluxes and budgets to better disentangle the effects of ocean acidification.
  • Boxhammer, Tim; Taucher, Jan; Bach, Lennart T.; Achterberg, Eric P.; Alguero-Muniz, Maria; Bellworthy, Jessica; Czerny, Jan; Esposito, Mario; Haunost, Mathias; Hellemann, Dana; Ludwig, Andrea; Yong, Jaw C.; Zark, Maren; Riebesell, Ulf; Anderson, Leif G. (2018)
    Ongoing acidification of the ocean through uptake of anthropogenic CO2 is known to affect marine biota and ecosystems with largely unknown consequences for marine food webs. Changes in food web structure have the potential to alter trophic transfer, partitioning, and biogeochemical cycling of elements in the ocean. Here we investigated the impact of realistic end-of-the-century CO2 concentrations on the development and partitioning of the carbon, nitrogen, phosphorus, and silica pools in a coastal pelagic ecosystem (Gullmar Fjord, Sweden). We covered the entire winter-to-summer plankton succession (100 days) in two sets of five pelagic mesocosms, with one set being CO2 enriched (similar to 760 mu atm pCO(2)) and the other one left at ambient CO2 concentrations. Elemental mass balances were calculated and we highlight important challenges and uncertainties we have faced in the closed mesocosm system. Our key observations under high CO2 were: (1) A significantly amplified transfer of carbon, nitrogen, and phosphorus from primary producers to higher trophic levels, during times of regenerated primary production. (2) A prolonged retention of all three elements in the pelagic food web that significantly reduced nitrogen and phosphorus sedimentation by about 11 and 9%, respectively. (3) A positive trend in carbon fixation (relative to nitrogen) that appeared in the particulate matter pool as well as the downward particle flux. This excess carbon counteracted a potential reduction in carbon sedimentation that could have been expected from patterns of nitrogen and phosphorus fluxes. Our findings highlight the potential for ocean acidification to alter partitioning and cycling of carbon and nutrients in the surface ocean but also show that impacts are temporarily variable and likely depending upon the structure of the plankton food web.
  • Schurgers, G.; Hickler, T.; Miller, P. A.; Arneth, A. (2009)
  • Heinonsalo, Jussi; Sun, Hui; Santalahti, Minna; Bäcklund, Kirsi; Hari, Pertti; Pumpanen, Jukka (2015)
    Ectomycorrhizal (ECM) symbiosis has been proposed to link plant photosynthesis and soil organic matter (SOM) decomposition through the production of fungal enzymes which promote SOM degradation and nitrogen (N) uptake. However, laboratory and field evidence for the existence of these processes are rare. Piloderma sp., a common ECM genus in boreal forest soil, was chosen as model mycorrhiza for this study. The abundance of Piloderma sp. was studied in root tips and soil over one growing season and in winter. Protease production was measured from ectomycorrhiza and soil solution in the field and pure fungal cultures. We also tested the effect of Piloderma olivaceum on host plant organic N nutrition in the laboratory. The results showed that Piloderma sp. was highly abundant in the field and produced extracellular proteases, which correlated positively with the gross primary production, temperature and soil respiration. In the laboratory, Piloderma olivaceum could improve the ability of Pinus sylvestris L. to utilize N from extragenous proteins. We suggest that ECM fungi, although potentially retaining N in their hyphae, are important in forest C and N cycling due to their ability to access proteinaeous N. As Piloderma sp. abundance appeared to be seasonally highly variable, recycling of fungal-bound N after hyphal death may therefore be of primary importance for the N cycling in boreal ecosystems.
  • Johansson, Karin S. L.; El-Soda, Mohamed; Pagel, Ellen; Meyer, Rhonda C.; Toldsepp, Kadri; Nilsson, Anders K.; Brosche, Mikael; Kollist, Hannes; Uddling, Johan; Andersson, Mats X. (2020)
    Background and Aims The stomatal conductance (g(s)) of most plant species decreases in response to elevated atmospheric CO2 concentration. This response could have a significant impact on plant water use in a future climate. However, the regulation of the CO2 induced stomatal closure response is not fully understood. Moreover, the potential genetic links between short-term (within minutes to hours) and long-term (within weeks to months) responses of g(s) to increased atmospheric CO2 have not been explored. Methods We used Arabidopsis thaliana recombinant inbred lines originating from accessions Col-0 (strong CO2 response) and C24 (weak CO2 response) to study short- and long-term controls of g(s) Quantitative trait locus (QTL) mapping was used to identify loci controlling short- and long-term g(s) responses to elevated CO2 as well as other stomata-related traits. Key Results Short- and long-term stomatal responses to elevated CO2 were significantly correlated. Both short-and long-term responses were associated with a QTL, at the end of chromosome 2. The location of this QTL was confirmed using near-isogonic lines and it was fine-mapped to a 410-kb region. The QTL did not correspond to any known gene involved in stomatal closure and had no effect on the responsiveness to abscisic acid. Additionally, we identified numerous other loci associated with stomatal regulation. Conclusions We identified and confirmed the effect of a strong QTL corresponding to a yet unknown regulator of stomatal closure in response to elevated CO2 concentration. The correlation between short- and long-term stomatal CO2 responses and the genetic link between these traits highlight the importance of understanding guard cell CO2 signalling to predict and manipulate plant water use in a world with increasing atmospheric CO2 concentration. This study demonstrates the power of using natural variation to unravel the genetic regulation of complex traits.
  • Thomas, H. J. D.; Bjorkman, A. D.; Myers-Smith, I. H.; Elmendorf, S. C.; Kattge, J.; Diaz, S.; Vellend, M.; Blok, D.; Cornelissen, J. H. C.; Forbes, B. C.; Henry, G. H. R.; Hollister, R. D.; Normand, S.; Prevéy, J. S.; Rixen, C.; Schaepman-Strub, G.; Wilmking, M.; Wipf, S.; Cornwell, W. K.; Beck, P. S. A.; Georges, D.; Goetz, S. J.; Guay, K. C.; Rüger, N.; Soudzilovskaia, N. A.; Spasojevic, M. J.; Alatalo, J. M.; Alexander, H. D.; Anadon-Rosell, A.; Angers-Blondin, S.; te Beest, M.; Berner, L. T.; Björk, R. G.; Buchwal, A.; Buras, A.; Carbognani, M.; Christie, K. S.; Collier, L. S.; Cooper, E. J.; Elberling, B.; Eskelinen, A.; Frei, E. R.; Grau, O.; Grogan, P.; Hallinger, M.; Heijmans, M. M. P. D.; Hermanutz, L.; Hudson, J. M. G.; Johnstone, J. F.; Hülber, K.; Iturrate-Garcia, M.; Iversen, C. M.; Jaroszynska, F.; Kaarlejarvi, E.; Kulonen, A.; Lamarque, L. J.; Lantz, T. C.; Lévesque, E.; Little, C. J.; Michelsen, A.; Milbau, A.; Nabe-Nielsen, J.; Nielsen, S. S.; Ninot, J. M.; Oberbauer, S. F.; Olofsson, J.; Onipchenko, V. G.; Petraglia, A.; Rumpf, S. B.; Shetti, R.; Speed, J. D. M.; Suding, K. N.; Tape, K. D.; Tomaselli, M.; Trant, A. J.; Treier, U. A.; Tremblay, M.; Venn, S. E.; Vowles, T.; Weijers, S.; Wookey, P. A.; Zamin, T. J.; Bahn, M.; Blonder, B.; van Bodegom, P. M.; Bond-Lamberty, B.; Campetella, G.; Cerabolini, B. E. L.; Chapin, F. S.; Craine, J. M.; Dainese, M.; Green, W. A.; Jansen, S.; Kleyer, M.; Manning, P.; Niinemets, Ü.; Onoda, Y.; Ozinga, W. A.; Peñuelas, J.; Poschlod, P.; Reich, P. B.; Sandel, B.; Schamp, B. S.; Sheremetiev, S. N.; de Vries, F. T. (2020)
    The majority of variation in six traits critical to the growth, survival and reproduction of plant species is thought to be organised along just two dimensions, corresponding to strategies of plant size and resource acquisition. However, it is unknown whether global plant trait relationships extend to climatic extremes, and if these interspecific relationships are confounded by trait variation within species. We test whether trait relationships extend to the cold extremes of life on Earth using the largest database of tundra plant traits yet compiled. We show that tundra plants demonstrate remarkably similar resource economic traits, but not size traits, compared to global distributions, and exhibit the same two dimensions of trait variation. Three quarters of trait variation occurs among species, mirroring global estimates of interspecific trait variation. Plant trait relationships are thus generalizable to the edge of global trait-space, informing prediction of plant community change in a warming world.
  • Singh, Jaswinder; Cameron, Erin; Reitz, Thomas; Schädler, Martin; Eisenhauer, Nico (2021)
    Abstract The impacts of climate change on biodiversity can be modulated by other changing environmental conditions, e.g. induced by land-use change. The potential interactive effects of climate change and land use have rarely been studied for soil organisms. To test the effects of changing climatic conditions and land use on soil invertebrates, we examined earthworm communities across different seasons in different grassland-use types (intensively managed grassland, extensively managed meadow, and extensively managed sheep pasture).We predicted that the strength of climate change effects would vary with season and land use. Overall, extracted earthworm populations showed the strongest variations in response to the season, indicating major differences in activity patterns and extraction efficiency, while climate change and different grassland-use types had fewer and weaker effects. Future climate, characterized by slightly higher precipitation in spring and fall but a strong reduction during the summer, had positive effects on the abundance of extracted adult earthworms in spring but then reduced the abundance of active earthworms across the remaining seasons. In contrast, the total biomass of juveniles tended to be consistently lower under future climate conditions. Earthworm species responded differently to the climate change and different grassland management types, and these species-specific responses further varied strongly across seasons. Intensive grassland management had negative effects, due to plant community composition, while sheep grazing favoured earthworm populations, due to dung deposition. There were only limited interactive effects between climate and land use, which thus did not support our main hypothesis. Nevertheless, these results highlight the complex and context-dependent responses of earthworm communities and activity patterns to climate change, with potential consequences for long-term population dynamics and crucial ecosystem functions. This article is protected by copyright. All rights reserved.
  • Sampaio, E.; Franco Rodil, Ivan; Vaz-Pinto, F.; Fernandez, A.; Arenas, F. (2017)
    Since the past century, rising CO2 levels have led to global changes (ocean warming and acidification) with subsequent effects on marine ecosystems and organisms. Macroalgae-herbivore interactions have a main role in the regulation of marine community structure (top-down control). Gradients of warming prompt complex non-linear effects on organism metabolism, cascading into altered trophic interactions and community dynamics. However, not much is known on how will acidification and grazer assemblage composition shape these effects. Within this context, we aimed to assess the combined effects of warming gradients and acidification on macroalgae-herbivore interactions, using three cosmopolitan species, abundant in the Iberian Peninsula and closely associated in nature: the amphipod Melita palmata, the gastropod Gibbula umbilicalis, and the green macroalga Ulva rigida. Under two CO2 treatments (triangle CO2 similar or equal to 450 mu atm) across a temperature gradient (13.5, 16.6, 19.9 and 22.1 degrees C), two mesocosm experiments were performed to assess grazer consumption rates and macroalgae-herbivore interaction, respectively. Warming (Experiment I and II) and acidification (Experiment II) prompted negative effects in grazer's survival and species-specific differences in consumption rates. M. palmata was shown to be the stronger grazer per biomass (but not per capita), and also the most affected by climate stressors. Macroalgae-herbivore interaction strength was markedly shaped by the temperature gradient, while simultaneous acidification lowered thermal optimal threshold. In the near future, warming and acidification are likely to strengthen top-down control, but further increases in disturbances may lead to bottom-up regulated communities. Finally, our results suggest that grazer assemblage composition may modulate future macroalgae-herbivore interactions. (C) 2017 Elsevier Ltd. All rights reserved.
  • Berninger, Frank; Susiluoto, Sannamaija; Gianelle, Damiano; Bahn, Michael; Wohlfahrt, Georg; Sutton, Mark; Garcia-Pausas, Jordi; Gimeno, Cristina; Sanz, Maria J.; Dore, Sabina; Rogiers, Nele; Furger, Markus; Eugster, Werner; Balzarolo, Manuela; Teresa Sebastia, M.; Tenhunen, John; Staszewski, Tomasz; Cernusca, Alexander (2015)
    We studied carbon balances and carbon stocks of mountain rangelands and meadows in a network of 8 eddy covariance sites and 14 sites with biomass data in Europe. Net ecosystem exchange of pastures and extensively managed semi-natural rangelands were usually close to zero, while meadows fixed carbon, with the exception of one meadow that was established on a drained peatland. When we accounted for off-site losses and inputs also the carbon budget of meadows approached zero. Soil carbon stocks in these ecosystems were high, comparable to those of forest ecosystems, while carbon stocks in plant biomass were smaller. Since soil carbon stocks of abandoned mountain grasslands are as high as in managed ecosystems, it is likely that the widespread abandonment of mountain rangelands used currently as pastures will not lead to an immediate carbon sink in those ecosystems.
  • Córdova, Raúl; Hogarth, Nicholas; Kanninen, Markku (2019)
    Smallholder farming is considered one of the most vulnerable sectors to the impacts of climate change, variability, and extremes, especially in the developing world. This high vulnerability is due to the socioeconomic limitations and high environmental sensitivity which aect the biophysical and socioeconomic components of their farming systems. Therefore, systems’ functionality and farmers’ livelihoods will also be aected, with significant implications for global food security, land-use/land-cover change processes and agrobiodiversity conservation. Thus, less vulnerable and more resilient smallholder farming systems constitute an important requisite for sustainable land management and to safeguard the livelihoods of millions of rural and urban households. This study compares a comprehensive socioeconomic and environmental dataset collected in 2015–2016 based on household interviews of 30 farmers of highland agroforestry systems and 30 farmers of conventional agriculture systems, to determine which system provides better opportunities to reduce exposure and sensitivity. A modified Climate Change Questionnaire Version 2 of the World Overview of Conservation Approaches and Technologies (WOCAT) was applied to collect the data. The interview data are based on the perceptions of Kayambi indigenous farmers about the levels of exposure and sensitivity of their farming systems during the last decade. Descriptive statistics were applied to analyze the data from the 60 farms. Results indicate that both agroforesters and conventional farmers clearly perceived increases in temperature and reductions in precipitation for the last decade, and expected this trend to continue in the next decade. Furthermore, conventional farmers perceived greater exposure to droughts (20%), solar radiation (43%), and pests, weeds and disease outbreaks (40%) than agroforesters. Additionally, results emphasize the better ability of agroforestry systems to reduce exposure and sensitivity to climate change and variability. These findings support the well-known assumptions about the key role played by agroforestry systems for climate change adaptation and mitigation, especially in developing countries.
  • Shurpali, Narasinha J.; Rannik, Ullar; Jokinen, Simo; Lind, Saara; Biasi, Christina; Mammarella, Ivan; Peltola, Olli; Pihlatie, Mari; Hyvonen, Niina; Raty, Mari; Haapanala, Sami; Zahniser, Mark; Virkajarvi, Perttu; Vesala, Timo; Martikainen, Pertti J. (2016)
    Nitrous oxide (N2O) is an important greenhouse gas produced in soil and aquatic ecosystems. Its warming potential is 296 times higher than that of CO2. Most N2O emission measurements made so far are limited in temporal and spatial resolution causing uncertainties in the global N2O budget. Recent advances in laser spectroscopic techniques provide an excellent tool for area-integrated, direct and continuous field measurements of N2O fluxes using the eddy covariance method. By employing this technique on an agricultural site with four laser-based analysers, we show here that N2O exchange exhibits contrasting diurnal behaviour depending upon soil nitrogen availability. When soil N was high due to fertilizer application, N2O emissions were higher during daytime than during the night. However, when soil N became limited, emissions were higher during the night than during the day. These reverse diurnal patterns supported by isotopic analyses may indicate a dominant role of plants on microbial processes associated with N2O exchange. This study highlights the potential of new technologies in improving estimates of global N2O sources.