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Li H, Wang C, Zhang F, He Y, Shi P, Guo X, Wang J, Zhang L, Li Y, Cao G, Zhou H. Atmospheric water vapor and soil moisture jointly determine the spatiotemporal variations of CO 2 fluxes and evapotranspiration across the Qinghai-Tibetan Plateau grasslands. THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 791:148379. [PMID: 34412395 DOI: 10.1016/j.scitotenv.2021.148379] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Revised: 06/07/2021] [Accepted: 06/07/2021] [Indexed: 06/13/2023]
Abstract
Alpine grasslands play important functions in mitigating climate change and regulating water resources. However, the spatiotemporal variability of their carbon and water budgets remains unquantified. Here, 47 site-year observations of CO2 and water vapor fluxes (ET) are analyzed at sites situated along a hydrothermal gradient across the Qinghai-Tibetan Plateau, including an alpine wetland (wettest), an alpine shrub (coldest), an alpine meadow, an alpine meadow-steppe, and an alpine steppe (driest and warmest). The results show that the benchmarks for annual net ecosystem exchange (NEE) are -79.3, -77.8, -66.7, 20.2, and 100.9 g C m-2 year-1 at the meadow, shrub, meadow-steppe, steppe, and wetland, respectively. The peak daily NEE normalized by peak leaf area index converges to 0.93 g C m-2 d-1 at the 5 sites. Except in the wetland (722.8 mm), the benchmarks of annual ET fluctuate from 511.0 mm in the steppe to 589.2 mm in the meadow. Boosted regression trees-based analysis suggests that the enhanced vegetation index (EVI) and net radiation (Rn) determine the variations of growing season monthly CO2 fluxes and ET, respectively, although the effect is to some extent site-specific. Inter-annual variability in NEE, ecosystem respiration (RES), and ET are tightly (R2 > 0.60) related to the inter-growing season NEE, RES, and ET, respectively. Both annual RES and annual NEE are significantly constrained by annual gross primary productivity (GPP), with 85% of the per-unit GPP contributing to RES (R2 = 0.84) and 15% to NEE (R2 = 0.12). Annual GPP significantly correlates with annual ET alone at the drier sites of the meadow-steppe and the steppe, suggesting the coupling of carbon and water is moisture-dependent in alpine grasslands. Over half of the inter-annual spatial variability in GPP, RES, NEE, and ET is explained by EVI, atmospheric water vapor, topsoil water content, and bulk surface resistance (rs), respectively. Because the spatial variations of EVI and rs are strongly regulated by atmospheric water vapor (R2 = 0.48) and topsoil water content (R2 = 0.54), respectively, we conclude that atmospheric water vapor and topsoil water content, rather than the expected air/soil temperatures, drive the spatiotemporal variations in CO2 fluxes and ET across temperature-limited grasslands. These findings are critical for improving predictions of the carbon sequestration and water holding capacity of alpine grasslands.
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Affiliation(s)
- Hongqin Li
- College of Life Sciences, Luoyang Normal University, Luoyang, Henan 471934, China; Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810001, China
| | - Chunyu Wang
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810001, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Fawei Zhang
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810001, China; Qinghai Provincial Key Laboratory of Restoration Ecology in Cold Region, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810001, China; Institute of Sanjiangyuan National Park, Chinese Academy of Sciences, Xining, Qinghai 810001, China.
| | - Yongtao He
- Synthesis Research Center of Chinese Ecosystem Research Network, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Peili Shi
- Synthesis Research Center of Chinese Ecosystem Research Network, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Xiaowei Guo
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810001, China
| | - Junbang Wang
- Synthesis Research Center of Chinese Ecosystem Research Network, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Leiming Zhang
- Synthesis Research Center of Chinese Ecosystem Research Network, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
| | - Yingnian Li
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810001, China; Institute of Sanjiangyuan National Park, Chinese Academy of Sciences, Xining, Qinghai 810001, China.
| | - Guangmin Cao
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810001, China
| | - Huakun Zhou
- Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810001, China; Qinghai Provincial Key Laboratory of Restoration Ecology in Cold Region, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, Qinghai 810001, China
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Wang P, Sun H, Li XY, Song X, Yang X, Wu X, Hu X, Yao H, Ma J, Ma J. Seasonal variations in water flux compositions controlled by leaf development: isotopic insights at the canopy-atmosphere interface. INTERNATIONAL JOURNAL OF BIOMETEOROLOGY 2021; 65:1719-1732. [PMID: 33851245 DOI: 10.1007/s00484-021-02126-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2020] [Revised: 03/31/2021] [Accepted: 04/02/2021] [Indexed: 06/12/2023]
Abstract
Water-stable isotopes provide a valuable tool for tracing plant-water interactions, particularly evapotranspiration (ET) partitioning and leaf water dynamics at the plant-atmosphere interface. However, process-based investigations of plant/leaf development and the associated isotopic dynamics of water fluxes involving isotope enrichment at plant-atmosphere interfaces at the ecosystem scale remain challenging. In this study, in situ isotopic measurements and tracer-aided models were used to study the dynamic interactions between vegetation growth and the isotopic dynamics of water fluxes (ET, soil evaporation, and transpiration) involving isotope enrichment in canopy leaves in a multispecies grassland ecosystem. The day-to-day variations in the isotopic compositions of ET flux were mainly controlled by plant growth, which could be explained by the significant logarithmic relationship determined between the leaf area index and transpiration fraction. Leaf development promoted a significant increase in the isotopic composition of ET and led to a slight decrease in the isotopic composition of water in canopy leaves. The transpiration (evaporation) isoflux acted to increase (decrease) the δ18O of water vapor, and the total isoflux impacts depended on the seasonal tradeoffs between transpiration and evaporation. The isotopic evidence in ET fluxes demonstrates the biotic controls on day-to-day variations in water/energy flux partitioning through transpiration activity. This study emphasizes that stable isotopes of hydrogen and oxygen are effective tools for quantitative evaluations of the hydrological component partitioning of ecosystems and plant-climate interactions.
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Affiliation(s)
- Pei Wang
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China.
| | - Haitao Sun
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China
| | - Xiao-Yan Li
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China
| | - Xin Song
- College of Life Sciences and Oceanography, Shenzhen University, 3688 Nanshan Avenue, Shenzhen, 518000, Guangdong, China
| | - Xiaofan Yang
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China
| | - Xiuchen Wu
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China
| | - Xia Hu
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China
| | - Hongyun Yao
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China
| | - Jingjing Ma
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China
| | - Juanjuan Ma
- State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China
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de Oliveira G, Brunsell NA, Crews TE, DeHaan LR, Vico G. Carbon and water relations in perennial Kernza (Thinopyrum intermedium): An overview. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2020; 295:110279. [PMID: 32534616 DOI: 10.1016/j.plantsci.2019.110279] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Revised: 09/10/2019] [Accepted: 09/16/2019] [Indexed: 06/11/2023]
Abstract
Perennial crops have been proposed as a more sustainable alternative to annual crops, because they have extended growing seasons, continuous ground cover, reduced nutrient leakage, and sequester more carbon in the soils than annual crops. One example is intermediate wheatgrass (Thinopyrum intermedium), a perennial crop that has been used as a cool-season forage throughout the USA and Canada and also across its native range in Eurasia. Since the 1980's, intermediate wheatgrass has been under domestication to improve seed fertility and grain yield. Commercial products are being sold under the trade name Kernza, owned by The Land Institute, located in Salina, Kansas, USA. This review provides a comprehensive framework about the physical and biological aspects involving the water and carbon cycles in Kernza plants. The main aspects we highlight here are based on previous findings regarding Kernza: i) the ability of maintaining a relatively high water-use efficiency throughout the whole growing season, which is beneficial to mitigate water stress, representing an important physiological mean to acclimate under severe, unfavorable weather conditions, and ii) its higher evapotranspiration (ET) and net carbon uptake rates, particularly when compared to annual counterparts. Only a thorough multifaceted assessment of the repercussion for carbon and water fluxes of a shift from annual crops to Kernza will allow assessing the perspectives of such novel perennial crop to support food security and a number of ecosystem services, particularly under future climates.
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Affiliation(s)
- Gabriel de Oliveira
- Department of Geography and Atmospheric Science, University of Kansas, 1475 Jayhawk Blvd., Lawrence, KS, 66045, USA.
| | - Nathaniel A Brunsell
- Department of Geography and Atmospheric Science, University of Kansas, 1475 Jayhawk Blvd., Lawrence, KS, 66045, USA.
| | - Timothy E Crews
- The Land Institute, 2440 East Water Well Rd., Salina, KS, 67401, USA.
| | - Lee R DeHaan
- The Land Institute, 2440 East Water Well Rd., Salina, KS, 67401, USA.
| | - Giulia Vico
- Department of Crop Production Ecology, Swedish University of Agricultural Sciences, Ulls väg 16, Uppsala, 75007, Sweden.
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Erb KH, Luyssaert S, Meyfroidt P, Pongratz J, Don A, Kloster S, Kuemmerle T, Fetzel T, Fuchs R, Herold M, Haberl H, Jones CD, Marín-Spiotta E, McCallum I, Robertson E, Seufert V, Fritz S, Valade A, Wiltshire A, Dolman AJ. Land management: data availability and process understanding for global change studies. GLOBAL CHANGE BIOLOGY 2017; 23:512-533. [PMID: 27447350 DOI: 10.1111/gcb.13443] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Revised: 07/11/2016] [Accepted: 07/13/2016] [Indexed: 05/22/2023]
Abstract
In the light of daunting global sustainability challenges such as climate change, biodiversity loss and food security, improving our understanding of the complex dynamics of the Earth system is crucial. However, large knowledge gaps related to the effects of land management persist, in particular those human-induced changes in terrestrial ecosystems that do not result in land-cover conversions. Here, we review the current state of knowledge of ten common land management activities for their biogeochemical and biophysical impacts, the level of process understanding and data availability. Our review shows that ca. one-tenth of the ice-free land surface is under intense human management, half under medium and one-fifth under extensive management. Based on our review, we cluster these ten management activities into three groups: (i) management activities for which data sets are available, and for which a good knowledge base exists (cropland harvest and irrigation); (ii) management activities for which sufficient knowledge on biogeochemical and biophysical effects exists but robust global data sets are lacking (forest harvest, tree species selection, grazing and mowing harvest, N fertilization); and (iii) land management practices with severe data gaps concomitant with an unsatisfactory level of process understanding (crop species selection, artificial wetland drainage, tillage and fire management and crop residue management, an element of crop harvest). Although we identify multiple impediments to progress, we conclude that the current status of process understanding and data availability is sufficient to advance with incorporating management in, for example, Earth system or dynamic vegetation models in order to provide a systematic assessment of their role in the Earth system. This review contributes to a strategic prioritization of research efforts across multiple disciplines, including land system research, ecological research and Earth system modelling.
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Affiliation(s)
- Karl-Heinz Erb
- Institute of Social Ecology Vienna (SEC), Alpen-Adria Universitaet Klagenfurt, Wien, Graz, Schottenfeldgasse 29, Vienna, 1070, Austria
| | - Sebastiaan Luyssaert
- LSCE-IPSL CEA-CNRS-UVSQ, Orme des Merisiers, Gif-sur-Yvette, F-91191, France
- Department of Ecological Sciences, Vrije Universiteit Amsterdam, Amsterdam, 1081 HV, The Netherlands
| | - Patrick Meyfroidt
- Georges Lemaître Center for Earth and Climate Research, Earth and Life Institute, Université Catholique de Louvain, Place Louis Pasteur 3, Louvain-la-Neuve, 1348, Belgium
- F.R.S.-FNRS, Brussels, 1000, Belgium
| | - Julia Pongratz
- Max Planck Institute for Meteorology, Bundesstr. 53, Hamburg, D-20146, Germany
| | - Axel Don
- Thünen-Institute of Climate-Smart Agriculture, Bundesallee 50, Braunschweig, 38116, Germany
| | - Silvia Kloster
- Max Planck Institute for Meteorology, Bundesstr. 53, Hamburg, D-20146, Germany
| | - Tobias Kuemmerle
- Geography Department, Humboldt-University Berlin, Unter den Linden 6, Berlin, 10099, Germany
- Integrative Research Institute on Transformations in Human-Environment Systems (IRI THESys), Humboldt-University Berlin, Unter den Linden 6, Berlin, 10099, Germany
| | - Tamara Fetzel
- Institute of Social Ecology Vienna (SEC), Alpen-Adria Universitaet Klagenfurt, Wien, Graz, Schottenfeldgasse 29, Vienna, 1070, Austria
| | - Richard Fuchs
- Department of Earth Sciences, VU University Amsterdam, Amsterdam, The Netherlands
| | - Martin Herold
- Laboratory of Geoinformation Science and Remote Sensing, Wageningen University, Droevendaalsesteeg 3, Wageningen, 6708 PB, The Netherlands
| | - Helmut Haberl
- Institute of Social Ecology Vienna (SEC), Alpen-Adria Universitaet Klagenfurt, Wien, Graz, Schottenfeldgasse 29, Vienna, 1070, Austria
| | - Chris D Jones
- Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, UK
| | - Erika Marín-Spiotta
- Department of Geography, University of Wisconsin-Madison, 550 North Park Street, Madison, WI, 53706, USA
| | - Ian McCallum
- Ecosystems Services & Management Program, International Institute for Applied Systems Analysis (IIASA), Schlossplatz 1, Laxenburg, A-2361, Austria
| | - Eddy Robertson
- Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, UK
| | - Verena Seufert
- Institute for Resources, Environment and Sustainability (IRES), Liu Institute for Global Issues, University of British Columbia (UBC), 6476 NW Marine Drive, Vancouver, BC, V6T 1Z2, Canada
| | - Steffen Fritz
- Ecosystems Services & Management Program, International Institute for Applied Systems Analysis (IIASA), Schlossplatz 1, Laxenburg, A-2361, Austria
| | - Aude Valade
- Institut Pierre Simon Laplace, IPSL-CNRS-UPMC, Paris, France
| | | | - Albertus J Dolman
- Department of Earth Sciences, VU University Amsterdam, Amsterdam, The Netherlands
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Liu F, Chen Y, Lu H, Shao H. Albedo indicating land degradation around the Badain Jaran Desert for better land resources utilization. THE SCIENCE OF THE TOTAL ENVIRONMENT 2017; 578:67-73. [PMID: 27401279 DOI: 10.1016/j.scitotenv.2016.06.171] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 06/20/2016] [Indexed: 06/06/2023]
Abstract
Surface albedo is an easy access parameter in reflecting the status of both human disturbed soil and indirectly influenced area, whose characteristic is an important indicator in sustainable development under the background of global climate change. In this study, we employed meteorological data, MODIS 8-day BRDF/Albedo and LAI products from 2000 to 2014 to show the amelioration and mechanism around the Badain Jaran Desert. Results showed that the human-dominated afforestation activities significantly increased the leaf area index (LAI) in summer and autumn. Lower reflectance at visible band was sensed inside the desert compared with the ecozone and the lowest albedo at forested area. The contribution of soil and vegetation reflectance to surface albedo determined the linear sensitivity of albedo to LAI variation. Decreased albedo dominated the spatial-temporal pattern of the Badain Jaran Desert. This study suggested that surface albedo can be regarded as a useful index in indicating the change process and evaluating the sustainable development of biological management around the Badain Jaran Desert.
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Affiliation(s)
- Fengshan Liu
- Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, PR China; China National Engineering Research Center of JUNCAO Technology, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, PR China
| | - Ying Chen
- Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, PR China; Forestry College, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, PR China
| | - Haiying Lu
- Institute of Agro-Biotechnology, Jiangsu Academy of Agriculture Sciences, Nanjing 210014, PR China.
| | - Hongbo Shao
- Institute of Agro-Biotechnology, Jiangsu Academy of Agriculture Sciences, Nanjing 210014, PR China.
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Wohlfahrt G, Tasser E. A mobile system for quantifying the spatial variability of the surface energy balance: design and application. INTERNATIONAL JOURNAL OF BIOMETEOROLOGY 2015; 59:617-27. [PMID: 25063050 PMCID: PMC4429021 DOI: 10.1007/s00484-014-0875-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 06/25/2014] [Accepted: 07/13/2014] [Indexed: 06/03/2023]
Abstract
We present a mobile device for the quantification of the small-scale (a few square meters) spatial variability in the surface energy balance components and several auxiliary variables of short-statured (<1 m) canopies. The key element of the mobile device is a handheld four-component net radiometer for the quantification of net radiation, albedo and infrared surface temperature, which is complemented with measurements of air temperature, wind speed, soil temperature and soil water content. Data are acquired by a battery-powered data logger, which is mounted on a backpack together with the auxiliary sensors. The proposed device was developed to bridge between the spatial scales of satellite/airborne remote sensing and fixed, stationary tower-based measurements with an emphasis on micrometeorological, catchment hydrological and landscape-ecological research questions. The potential of the new device is demonstrated through four selected case studies, which cover the issues of net radiation heterogeneity within the footprint of eddy covariance flux measurements due to (1) land use and (2) slope and aspect of the underlying surface, (3) controls on landscape-scale variability in soil temperature and albedo and (4) the estimation of evapotranspiration based exclusively on measurements with the mobile device.
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Affiliation(s)
- Georg Wohlfahrt
- Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020, Innsbruck, Austria,
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A Study of Fitting a Swamp Meadow Ecosystem Evapotranspiration to a Model Based on the Penman-Monteith Equation. J CHEM-NY 2015. [DOI: 10.1155/2015/315708] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
To accurately estimate the magnitude and seasonal dynamics of evapotranspiration (ET) over an important a swamp meadow in the Fenghuoshan permafrost region, we employed the Food and Agriculture Organization- (FAO-) Penman-Monteith (P-M) model. The model was also used to investigate changes in the crop coefficient (kc), which was calculated as the ratio of the measured actual ET (ETafrom the eddy covariance (EC) system) to the reference ET (ET0from the P-M model). The results indicated a reference ET of 900 mm/year from the swamp meadow ecosystem, which was significantly higher than the actual ET (426 mm/year). The reference ET peaked from April to July, while the actual ET was primarily in growing season. The value ofkcexhibited significant seasonal variations within the range 0.3–1.0 with a meankcof 0.55 during the growing season. The dailykcshowed a linear increase withRnandTaand a linear decrease with the VPD. With respect to the biotic factors, the biomass exhibited a significant positive correlation withkc. Thus, a dailykcmodel is developed as a function of the VPD,Rn,Ta, and biomass.
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Hörtnagl L, Wohlfahrt G. Methane and nitrous oxide exchange over a managed hay meadow. BIOGEOSCIENCES (ONLINE) 2014; 11:7219-7236. [PMID: 25821473 PMCID: PMC4373549 DOI: 10.5194/bg-11-7219-2014] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The methane (CH4) and nitrous oxide (N2O) exchange of a temperate mountain grassland near Neustift, Austria, was measured during 2010-2012 over a time period of 22 months using the eddy covariance method. Exchange rates of both compounds at the site were low, with 97% of all half-hourly CH4 and N2O fluxes ranging between ±200 and ±50 ng m-2 s-1, respectively. The meadow acted as a sink for both compounds during certain time periods, but was a clear source of CH4 and N2O on an annual timescale. Therefore, both gases contributed to an increase of the global warming potential (GWP), effectively reducing the sink strength in terms of CO2 equivalents of the investigated grassland site. In 2011, our best guess estimate showed a net greenhouse gas (GHG) sink of -32 g CO2 equ. m-2 yr-1 for the meadow, whereby 55% of the CO2 sink strength of -71 g CO2m-2 yr-1 was offset by CH4 (N2O) emissions of 7 (32) g CO2 equ. m-2 yr-1. When all data were pooled, the ancillary parameters explained 27 (42)% of observed CH4 (N2O) flux variability, and up to 62 (76)% on shorter timescales in-between management dates. In the case of N2O fluxes, we found the highest emissions at intermediate soil water contents and at soil temperatures close to 0 or above 14 °C. In comparison to CO2, H2O and energy fluxes, the interpretation of CH4 and N2O exchange was challenging due to footprint heterogeneity regarding their sources and sinks, uncertainties regarding post-processing and quality control. Our results emphasize that CH4 and N2O fluxes over supposedly well-aerated and moderately fertilized soils cannot be neglected when evaluating the GHG impact of temperate managed grasslands.
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Affiliation(s)
- L. Hörtnagl
- Institute of Ecology, University of Innsbruck, Austria
| | - G. Wohlfahrt
- Institute of Ecology, University of Innsbruck, Austria
- European Academy of Bolzano, Bolzano, Italy
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Wohlfahrt G, Cremonese E, Hammerle A, Hörtnagl L, Galvagno M, Gianelle D, Marcolla B, di Cella UM. Tradeoffs between global warming and day length on the start of the carbon uptake period in seasonally cold ecosystems. GEOPHYSICAL RESEARCH LETTERS 2013; 40:6136-6142. [PMID: 24587563 PMCID: PMC3935172 DOI: 10.1002/2013gl058182] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Revised: 11/12/2013] [Accepted: 11/14/2013] [Indexed: 05/31/2023]
Abstract
It is well established that warming leads to longer growing seasons in seasonally cold ecosystems. Whether this goes along with an increase in the net ecosystem carbon dioxide (CO2) uptake is much more controversial. We studied the effects of warming on the start of the carbon uptake period (CUP) of three mountain grasslands situated along an elevational gradient in the Alps. To this end we used a simple empirical model of the net ecosystem CO2 exchange, calibrated and forced with multi-year empirical data from each site. We show that reductions in the quantity and duration of daylight associated with earlier snowmelts were responsible for diminishing returns, in terms of carbon gain, from longer growing seasons caused by reductions in daytime photosynthetic uptake and increases in nighttime losses of CO2. This effect was less pronounced at high, compared to low, elevations, where the start of the CUP occurred closer to the summer solstice when changes in day length and incident radiation are minimal.
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Affiliation(s)
- Georg Wohlfahrt
- Institute of Ecology, University of Innsbruck, Innsbruck, AUSTRIA
| | - Edoardo Cremonese
- Environmental Protection Agency of Aosta Valley, ARPA VdA, Climate Change Unit, Aosta, ITALY
| | - Albin Hammerle
- Institute of Ecology, University of Innsbruck, Innsbruck, AUSTRIA
| | - Lukas Hörtnagl
- Institute of Ecology, University of Innsbruck, Innsbruck, AUSTRIA
| | - Marta Galvagno
- Environmental Protection Agency of Aosta Valley, ARPA VdA, Climate Change Unit, Aosta, ITALY
| | - Damiano Gianelle
- Sustainable Agro-ecosystems and Bioresources Department, Research and Innovation Centre, Fondazione Edmund Mach, San Michele all'Adige, ITALY ; Foxlab, Research and Innovation Centre, Fondazione Edmund Mach, San Michele all'Adige, ITALY
| | - Barbara Marcolla
- Sustainable Agro-ecosystems and Bioresources Department, Research and Innovation Centre, Fondazione Edmund Mach, San Michele all'Adige, ITALY
| | - Umberto Morra di Cella
- Environmental Protection Agency of Aosta Valley, ARPA VdA, Climate Change Unit, Aosta, ITALY
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Hörtnagl L, Bamberger I, Graus M, Ruuskanen TM, Schnitzhofer R, Walser M, Unterberger A, Hansel A, Wohlfahrt G. Acetaldehyde exchange above a managed temperate mountain grassland. ATMOSPHERIC CHEMISTRY AND PHYSICS DISCUSSIONS : ACPD 2013; 13:10.5194/acpd-13-26117-2013. [PMID: 24363666 PMCID: PMC3868935 DOI: 10.5194/acpd-13-26117-2013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
An overview of acetaldehyde exchange above a managed temperate mountain grassland in Austria over four growing seasons is presented. The meadow acted as a net source of acetaldehyde in all four years, emitting between 7 and 28 mg C m-2 over the whole growing period. The cutting of the meadow resulted in huge acetaldehyde emission bursts on the day of harvesting or one day later. During undisturbed conditions, both uptake and emission fluxes were recorded. The bidirectional nature of acetaldehyde fluxes was also reflected by clear diurnal cycles during certain time periods, indicating strong deposition processes before the 1st cut and emission towards the end of the growing season. The analysis of acetaldehyde compensation points revealed a complex relationship between ambient acetaldehyde mixing ratios and respective fluxes, significantly influenced by multiple environmental parameters and variable throughout the year. As a major finding of this study, we identified both a positive and negative correlation between concentration and flux on a daily scale, where soil temperature and soil water content were the most significant factors in determining the direction of the slope. In turn, this bidirectional relationship on a daily scale resulted in compensation points between 0.40 ppbv and 0.54 ppbv, which could be well explained by collected ancillary data. We conclude that in order to model acetaldehyde fluxes at the site in Neustift on a daily scale over longer time periods, it is crucial to know the type of relationship, i.e. the direction of the slope, between mixing ratios and fluxes on a given day.
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Affiliation(s)
- L. Hörtnagl
- Institute of Ecology, University of Innsbruck, Austria
| | - I. Bamberger
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
| | - M. Graus
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
| | - T. M. Ruuskanen
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
| | - R. Schnitzhofer
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
| | - M. Walser
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
| | - A. Unterberger
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
| | - A. Hansel
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
| | - G. Wohlfahrt
- Institute of Ecology, University of Innsbruck, Austria
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11
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Wohlfahrt G, Widmoser P. Can an energy balance model provide additional constraints on how to close the energy imbalance? AGRICULTURAL AND FOREST METEOROLOGY 2013; 169:85-91. [PMID: 24465072 PMCID: PMC3898304 DOI: 10.1016/j.agrformet.2012.10.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Revised: 10/04/2012] [Accepted: 10/15/2012] [Indexed: 06/03/2023]
Abstract
Elucidating the causes for the energy imbalance, i.e. the phenomenon that eddy covariance latent and sensible heat fluxes fall short of available energy, is an outstanding problem in micrometeorology. This paper tests the hypothesis that the full energy balance, through incorporation of additional independent measurements which determine the driving forces of and resistances to energy transfer, provides further insights into the causes of the energy imbalance and additional constraints on energy balance closure options. Eddy covariance and auxiliary data from three different biomes were used to test five contrasting closure scenarios. The main result of our study is that except for nighttime, when fluxes were low and noisy, the full energy balance generally did not contain enough information to allow further insights into the causes of the imbalance and to constrain energy balance closure options. Up to four out of the five tested closure scenarios performed similarly and in up to 53% of all cases all of the tested closure scenarios resulted in plausible energy balance values. Our approach may though provide a sensible consistency check for eddy covariance energy flux measurements.
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Affiliation(s)
- Georg Wohlfahrt
- Institute for Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
| | - Peter Widmoser
- Hydrology and Water Resources Management Department, Ecology Centre, University of Kiel, Olshausenstrasse 40, 24098 Kiel, Germany
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12
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Brilli F, Hörtnagl L, Bamberger I, Schnitzhofer R, Ruuskanen TM, Hansel A, Loreto F, Wohlfahrt G. Qualitative and quantitative characterization of volatile organic compound emissions from cut grass. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2012; 46:3859-65. [PMID: 22409212 PMCID: PMC3857492 DOI: 10.1021/es204025y] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Mechanical wounding of plants triggers the release of a blend of reactive biogenic volatile organic compounds (BVOCs). During and after mowing and harvesting of managed grasslands, significant BVOC emissions have the potential to alter the physical and chemical properties of the atmosphere and lead to ozone and aerosol formation with consequences for regional air quality. We show that the amount and composition of BVOCs emitted per unit dry weight of plant material is comparable between laboratory enclosure measurements of artificially severed grassland plant species and in situ ecosystem-scale flux measurements above a temperate mountain grassland during and after periodic mowing and harvesting. The investigated grassland ecosystem emitted annually up to 130 mg carbon m(-2) in response to cutting and drying, the largest part being consistently represented by methanol and a blend of green leaf volatiles (GLV). In addition, we report the plant species-specific emission of furfural, terpenoid-like compounds (e.g., camphor), and sesquiterpenes from cut plant material, which may be used as tracers for the presence of given plant species in the ecosystem.
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Affiliation(s)
- Federico Brilli
- Ionicon Analytik GmbH, Eduard-Bodem-Gasse 3, 6020 - Innsbruck, AUSTRIA
| | - Lukas Hörtnagl
- Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
| | - Ines Bamberger
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Technikerstr. 25, 6020 Innsbruck, AUSTRIA
| | - Ralf Schnitzhofer
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Technikerstr. 25, 6020 Innsbruck, AUSTRIA
| | - Taina M. Ruuskanen
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Technikerstr. 25, 6020 Innsbruck, AUSTRIA
| | - Armin Hansel
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Technikerstr. 25, 6020 Innsbruck, AUSTRIA
| | - Francesco Loreto
- National Research Council, Institute for Plant Protection (CNR-IPP), Via Madonna del Piano 10, 50019 - Sesto Fiorentino, Firenze, ITALY
| | - Georg Wohlfahrt
- Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
- Corresponding author: Georg Wohlfahrt Tel ++43 (0)512 5075977 Fax ++43 (0)512 5072975
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13
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Brilli F, Hörtnagl L, Hammerle A, Haslwanter A, Hansel A, Loreto F, Wohlfahrt G. Leaf and ecosystem response to soil water availability in mountain grasslands. AGRICULTURAL AND FOREST METEOROLOGY 2011; 151:1731-1740. [PMID: 24465071 PMCID: PMC3899607 DOI: 10.1016/j.agrformet.2011.07.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Climate change is expected to affect the Alps by increasing the frequency and intensity of summer drought events with negative impacts on ecosystem water resources. The response of CO2 and H2O exchange of a mountain grassland to natural fluctuations of soil water content was evaluated during 2001-2009. In addition, the physiological performance of individual mountain forb and graminoid plant species under progressive soil water shortage was explored in a laboratory drought experiment. During the 9-year study period the natural occurrence of moderately to extremely dry periods did not lead to substantial reductions in net ecosystem CO2 exchange and evapotranspiration. Laboratory drought experiments confirmed that all the surveyed grassland plant species were insensitive to progressive soil drying until very low soil water contents (<0.01 m3 m-3) were reached after several days of drought. In field conditions, such a low threshold was never reached. Re-watering after a short-term drought event (5±1 days) resulted in a fast and complete recovery of the leaf CO2 and H2O gas exchange of the investigated plant species. We conclude that the present-day frequency and intensity of dry periods does not substantially affect the functioning of the investigated grassland ecosystem. During dry periods the observed "water spending" strategy employed by the investigated mountain grassland species is expected to provide a cooling feedback on climate warming, but may have negative consequences for down-stream water users.
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Affiliation(s)
- Federico Brilli
- Ionicon Analytik GmbH, Eduard-Bodem-Gasse 3, 6020 Innsbruck, AUSTRIA
| | - Lukas Hörtnagl
- Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
| | - Albin Hammerle
- Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
| | - Alois Haslwanter
- Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
| | - Armin Hansel
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Technikerstr. 25, 6020 Innsbruck, AUSTRIA
| | - Francesco Loreto
- National Research Council, Institute for the Protection of Plants, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze, ITALY
| | - Georg Wohlfahrt
- Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
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14
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Hörtnagl L, Bamberger I, Graus M, Ruuskanen TM, Schnitzhofer R, Müller M, Hansel A, Wohlfahrt G. Biotic, abiotic and management controls on methanol exchange above a temperate mountain grassland. JOURNAL OF GEOPHYSICAL RESEARCH. BIOGEOSCIENCES 2011; 116:G03021. [PMID: 24349901 PMCID: PMC3859319 DOI: 10.1029/2011jg001641] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Methanol (CH3OH) fluxes were quantified above a managed temperate mountain grassland in the Stubai Valley (Tyrol, Austria) during the growing seasons 2008 and 2009. Half-hourly methanol fluxes were calculated by means of the virtual disjunct eddy covariance (vDEC) method using 3-dimensional wind data from a sonic anemometer and methanol volume mixing ratios measured with a proton-transfer-reaction mass spectrometer (PTR-MS). During (undisturbed) mature and growing phases methanol fluxes exhibited a clear diurnal cycle with close-to-zero fluxes during nighttime and emissions, up to 10 nmol m-2 s-1, which followed the diurnal course of radiation and air temperature. Management events were found to represent the largest perturbations of methanol exchange at the studied grassland ecosystem: Peak emissions of 144.5 nmol m-2 s-1 were found during/after cutting of the meadow reflecting the wounding of the plant material and subsequent depletion of the leaf internal aqueous methanol pools. After the application of organic fertilizer, elevated methanol emissions of up to 26.7 nmol m-2 s-1 were observed, likely reflecting enhanced microbial activity associated with the applied manure. Simple and multiple linear regression analyses revealed air temperature and radiation as the dominant abiotic controls, jointly explaining 47 % and 70 % of the variability in half-hourly and daily methanol fluxes. In contrast to published leaf-level laboratory studies, the surface conductance and the daily change in the amount of green plant area, used as ecosystem-scale proxies for stomatal conductance and growth, respectively, were found to exert only minor biotic controls on methanol exchange.
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Affiliation(s)
| | - Ines Bamberger
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
| | - Martin Graus
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria ; Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309
| | - Taina M Ruuskanen
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
| | - Ralf Schnitzhofer
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
| | - Markus Müller
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
| | - Armin Hansel
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
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15
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Ruuskanen TM, Müller M, Schnitzhofer R, Karl T, Graus M, Bamberger I, Hörtnagl L, Brilli F, Wohlfahrt G, Hansel A. Eddy covariance VOC emission and deposition fluxes above grassland using PTR-TOF. ATMOSPHERIC CHEMISTRY AND PHYSICS 2011; 11:10.5194/acp-11-611-2011. [PMID: 24348524 PMCID: PMC3859318 DOI: 10.5194/acp-11-611-2011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Eddy covariance (EC) is the preferable technique for flux measurements since it is the only direct flux determination method. It requires a continuum of high time resolution measurements (e.g. 5-20 Hz). For volatile organic compounds (VOC) soft ionization via proton transfer reaction has proven to be a quantitative method for real time mass spectrometry; here we use a proton transfer reaction time of flight mass spectrometer (PTR-TOF) for 10 Hz EC measurements of full mass spectra up to m/z 315. The mass resolution of the PTR-TOF enabled the identification of chemical formulas and separation of oxygenated and hydrocarbon species exhibiting the same nominal mass. We determined 481 ion mass peaks from ambient air concentration above a managed, temperate mountain grassland in Neustift, Stubai Valley, Austria. During harvesting we found significant fluxes of 18 compounds distributed over 43 ions, including protonated parent compounds, as well as their isotopes and fragments and VOC-H+ - water clusters. The dominant BVOC fluxes were methanol, acetaldehyde, ethanol, hexenal and other C6 leaf wound compounds, acetone, acetic acid, monoterpenes and sequiterpenes. The smallest reliable fluxes we determined were less than 0.1 nmol m-2 s-1, as in the case of sesquiterpene emissions from freshly cut grass. Terpenoids, including mono- and sesquiterpenes, were also deposited to the grassland before and after the harvesting. During cutting, total VOC emission fluxes up to 200 nmolC m-2 s-1 were measured. Methanol emissions accounted for half of the emissions of oxygenated VOCs and a third of the carbon of all measured VOC emissions during harvesting.
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Affiliation(s)
- T. M. Ruuskanen
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
| | - M. Müller
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
- Ionicon Analytik, Innsbruck, Austria
| | - R. Schnitzhofer
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
- Ionicon Analytik, Innsbruck, Austria
| | - T. Karl
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
- Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO 80307, USA
| | - M. Graus
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
| | - I. Bamberger
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
| | - L. Hörtnagl
- Institute of Ecology, University of Innsbruck, Innsbruck, Austria
| | - F. Brilli
- Ionicon Analytik, Innsbruck, Austria
| | - G. Wohlfahrt
- Institute of Ecology, University of Innsbruck, Innsbruck, Austria
| | - A. Hansel
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
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16
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Wohlfahrt G, Irschick C, Thalinger B, Hörtnagl L, Obojes N, Hammerle A. Multiple constraints on grassland evapotranspiration: implications for closing the energy balance. VADOSE ZONE JOURNAL : VZJ 2010; 9:0.2136/vzj2009.0158. [PMID: 24339743 PMCID: PMC3857019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
When using the eddy covariance (EC) method for measuring the ecosystem-atmosphere exchange of sensible and latent heat, it is not uncommon to find that these two energy fluxes fall short of available energy by 20-30 %. As the causes for the energy imbalance are still under discussion, it is currently not clear how the energy balance should be closed. The objective of the present paper is to use independent measurements of evapotranspiration (ET) for empirically devising on how to best close the energy balance. To this end ET of a temperate mountain grassland was quantified during two measurement campaigns using both an open- and a closed-path EC system, lysimeters and an approach scaling up leaf-level stomatal conductance to canopy level transpiration. Our study showed that both EC systems underestimated ET measured independently by lysimeters and the up-scaling approach. Best correspondence to independently measured ET was achieved by assigning the entire energy imbalance to ET and by adjusting ET according to the average energy balance ratio during the first and second measurement campaign, respectively. Due to a large spatial variability in ET during the first measurement campaign and given large differences in spatial scale between the EC and the independent methods, we are more confident with the comparison of approaches during the second measurement campaign and thus recommend forcing energy balance closure by adjusting for the average energy balance ratio.
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Affiliation(s)
- Georg Wohlfahrt
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
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17
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Wang K, Dickinson RE, Wild M, Liang S. Evidence for decadal variation in global terrestrial evapotranspiration between 1982 and 2002: 1. Model development. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009jd013671] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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18
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Bamberger I, Hortnagl L, Schnitzhofer R, Graus M, Ruuskanen TM, Muller M, Dunkl J, Wohlfahrt G, Hansel A. BVOC fluxes above mountain grassland. ACTA ACUST UNITED AC 2010; 7. [PMID: 24339833 DOI: 10.5194/bg-7-1413-2010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Grasslands comprise natural tropical savannah over managed temperate fields to tundra and cover one quarter of the Earth's land surface. Plant growth, maintenance and decay result in volatile organic compound (VOCs) emissions to the atmosphere. Furthermore, biogenic VOCs (BVOCs) are emitted as a consequence of various environmental stresses including cutting and drying during harvesting. Fluxes of BVOCs were measured with a proton-transfer-reaction-mass-spectrometer (PTR-MS) over temperate mountain grassland in Stubai Valley (Tyrol, Austria) over one growing season (2008). VOC fluxes were calculated from the disjunct PTR-MS data using the virtual disjunct eddy covariance method and the gap filling method. Methanol fluxes obtained with the two independent flux calculation methods were highly correlated (y = 0.95×-0.12, R2 = 0.92). Methanol showed strong daytime emissions throughout the growing season - with maximal values of 9.7 nmol m-2 s-1, methanol fluxes from the growing grassland were considerably higher at the beginning of the growing season in June compared to those measured during October (2.5 nmol m-2 s-1). Methanol was the only component that exhibited consistent fluxes during the entire growing periods of the grass. The cutting and drying of the grass increased the emissions of methanol to up to 78.4 nmol m-2 s-1. In addition, emissions of acetaldehyde (up to 11.0 nmol m-2 s-1), and hexenal (leaf aldehyde, up to 8.6 nmol m-2 s-1) were detected during/after harvesting.
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Affiliation(s)
- I Bamberger
- Institute of Ion Physics and Applied Physics, University of Innsbruck, Austria
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19
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Hörtnagl L, Clement R, Graus M, Hammerle A, Hansel A, Wohlfahrt G. Dealing with disjunct concentration measurements in eddy covariance applications: a comparison of available approaches. ATMOSPHERIC ENVIRONMENT (OXFORD, ENGLAND : 1994) 2010; 44:http://dx.doi.org/10.1016/j.atmosenv.2010.02.042. [PMID: 24339727 PMCID: PMC3856879 DOI: 10.1016/j.atmosenv.2010.02.042] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Using proton transfer reaction mass spectrometry equipped with a quadrupol mass analyser to quantify the biosphere-atmosphere exchange of volatile organic compounds (VOC), concentrations of different VOC are measured sequentially. Depending on how many VOC species are targeted and their respective integration times, each VOC is measured at repeat rates on the order of a few seconds. This represents an order of magnitude longer sample interval compared to the standard eddy covariance (EC) method (5-20 Hz sampling rates). Here we simulate the effect of disjunct sampling on EC flux estimates by decreasing the time resolution of CO2 and H2O concentrations measured at 20 Hz above a temperate mountain grassland in the Austrian Alps. Fluxes for one month are calculated with the standard EC method and compared to fluxes calculated based on the disjunct data (1, 3 and 5 s sampling rates) using the following approaches: i) imputation of missing concentrations based on the nearest neighbouring samples (iDECnn), ii) imputation by linear interpolation (iDECli), and iii) virtual disjunct EC (vDEC), i.e. flux calculation based solely on the disjunct concentrations. It is shown that the two imputation methods result in additional low-pass filtering, longer lag times (as determined with the maximum cross-correlation method) and a flux loss of 3-30 % as compared to the standard EC method. A novel procedure, based on a transfer function approach, which specifically corrects for the effect of data treatment, was developed, resulting in improved correspondence (to within 2 %). The vDEC method yields fluxes which approximate the true (20 Hz) fluxes to within 3-7 % and it is this approach we recommend because it involves no additional empirical corrections. The only drawback of the vDEC method is the noisy nature of the cross-correlations, which poses problems with lag determination - practical approaches to overcome this limitation are discussed.
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Affiliation(s)
- Lukas Hörtnagl
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
| | - Robert Clement
- School of Geosciences, University of Edinburgh, Crew Building, The King’s Buildings, West Mains Road, EH9 3JN Edinburgh, UK
| | - Martin Graus
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria
| | - Albin Hammerle
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
| | - Armin Hansel
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria
| | - Georg Wohlfahrt
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
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20
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Müller M, Graus M, Ruuskanen TM, Schnitzhofer R, Bamberger I, Kaser L, Titzmann T, Hörtnagl L, Wohlfahrt G, Karl T, Hansel A. First eddy covariance flux measurements by PTR-TOF. ATMOSPHERIC MEASUREMENT TECHNIQUES 2010; 3:387-395. [PMID: 24465280 PMCID: PMC3898015 DOI: 10.5194/amt-3-387-2010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The recently developed PTR-TOF instrument was evaluated to measure methanol fluxes emitted from grass land using the eddy covariance method. The high time resolution of the PTR-TOF allowed storing full mass spectra up to m/z 315 with a frequency of 10 Hz. Three isobaric ions were found at a nominal mass of m/z 33 due to the high mass resolving power of the PTR-TOF. Only one of the three peaks contributed to eddy covariance fluxes. The exact mass of this peak agrees well with the exact mass of protonated methanol (m/z 33.0335). The eddy covariance methanol fluxes measured with PTR-TOF were compared to virtual disjunct eddy covariance methanol fluxes simultaneously measured with a conventional PTR-MS. The methanol fluxes from both instruments show excellent agreement.
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Affiliation(s)
- M. Müller
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
- Ionicon Analytik, Innsbruck, Austria
| | - M. Graus
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - T. M. Ruuskanen
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - R. Schnitzhofer
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
- Ionicon Analytik, Innsbruck, Austria
| | - I. Bamberger
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - L. Kaser
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - T. Titzmann
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - L. Hörtnagl
- Institut für Ökologie, Universität Innsbruck, Innsbruck, Austria
| | - G. Wohlfahrt
- Institut für Ökologie, Universität Innsbruck, Innsbruck, Austria
| | - T. Karl
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
- Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO 80307, USA
| | - A. Hansel
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
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21
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Wohlfahrt G, Pilloni S, Hörtnagl L, Hammerle A. Estimating carbon dioxide fluxes from temperate mountain grasslands using broad-band vegetation indices. ACTA ACUST UNITED AC 2010; 7:683-694. [PMID: 24339832 DOI: 10.5194/bg-7-683-2010] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The broad-band normalised difference vegetation index (NDVI) and the simple ratio (SR) were calculated from measurements of reflectance of photosynthetically active and short-wave radiation at two temperate mountain grasslands in Austria and related to the net ecosystem CO2 exchange (NEE) measured concurrently by means of the eddy covariance method. There was no significant statistical difference between the relationships of midday mean NEE with narrow- and broad-band NDVI and SR, measured during and calculated for that same time window, respectively. The skill of broad-band NDVI and SR in predicting CO2 fluxes was higher for metrics dominated by gross photosynthesis and lowest for ecosystem respiration, with NEE in between. A method based on a simple light response model whose parameters were parameterised based on broad-band NDVI allowed to improve predictions of daily NEE and is suggested to hold promise for filling gaps in the NEE time series. Relationships of CO2 flux metrics with broad-band NDVI and SR however generally differed between the two studied grassland sites indicting an influence of additional factors not yet accounted for.
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Affiliation(s)
- G Wohlfahrt
- Institute of Ecology, University of Innsbruck, Innsbruck, Austria
| | - S Pilloni
- Institute of Ecology, University of Innsbruck, Innsbruck, Austria
| | - L Hörtnagl
- Institute of Ecology, University of Innsbruck, Innsbruck, Austria
| | - A Hammerle
- Institute of Ecology, University of Innsbruck, Innsbruck, Austria
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22
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Wohlfahrt G, Hörtnagl L, Hammerle A, Graus M, Hansel A. Measuring eddy covariance fluxes of ozone with a slow-response analyser. ATMOSPHERIC ENVIRONMENT (OXFORD, ENGLAND : 1994) 2009; 43:10.1016/j.atmosenv.2009.06.031. [PMID: 24348085 PMCID: PMC3859896 DOI: 10.1016/j.atmosenv.2009.06.031] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Ozone (O3) fluxes above a temperate mountain grassland were measured by means of the eddy covariance (EC) method using a slow-response O3 analyser. The resultant flux loss was corrected for by a series of transfer functions which model the various sources of high- and, in particular, low-pass filtering. The resulting correction factors varied on average between 1.7 and 3.5 during night and day time, respectively. A cospectral analysis confirmed the accuracy of this approach. O3 fluxes were characterised by a comparatively large random uncertainty, which during daytime typically amounted to 60 %. EC O3 fluxes were compared against O3 flux measurements made concurrently with the flux-gradient (FG) method. The two methods generally agreed well, except for a period between sun rise and early afternoon, when the FG method was suspected of being affected by the presence of photochemical sources/sinks. O3 flux magnitudes and deposition velocities determined with the EC method compared nicely with the available literature from grassland studies. We conclude that our understanding of the causes and consequences of various sources of flux loss (associated with any EC system) has sufficiently matured so that also less-than-ideal instrumentation may be used in EC flux applications, albeit at the cost of relatively large empirical corrections.
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Affiliation(s)
- Georg Wohlfahrt
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
| | - Lukas Hörtnagl
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
| | - Albin Hammerle
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
| | - Martin Graus
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, 6020 Innsbruck, AUSTRIA
| | - Armin Hansel
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, 6020 Innsbruck, AUSTRIA
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23
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Wohlfahrt G, Haslwanter A, Hörtnagl L, Jasoni RL, Fenstermaker LF, Arnone JA, Hammerle A. On the consequences of the energy imbalance for calculating surface conductance to water vapour. AGRICULTURAL AND FOREST METEOROLOGY 2009; 149:1556-1559. [PMID: 24465070 PMCID: PMC3898014 DOI: 10.1016/j.agrformet.2009.03.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The Penman-Monteith combination equation, which is most frequently used to derive the surface conductance to water vapour (Gs), implicitly assumes the energy balance to be closed. Any energy imbalance (positive or negative) will thus affect the calculated Gs. Using eddy covariance energy flux data from a temperate grassland and a desert shrub ecosystem we explored five possible approaches of closing the energy imbalance and show that calculated Gs may differ considerably between these five approaches depending on the relative magnitudes of sensible and latent heat fluxes, and the magnitude and sign of the energy imbalance. Based on our limited understanding of the nature of the energy imbalance, we tend to favour an approach which preserves the Bowen-ratio and closes the energy balance on a larger time scale.
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Affiliation(s)
- Georg Wohlfahrt
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
| | - Alois Haslwanter
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
| | - Lukas Hörtnagl
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
| | - Richard L. Jasoni
- Division of Earth and Ecosystem Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno NV 89512, USA
| | - Lynn F. Fenstermaker
- Division of Earth and Ecosystem Sciences, Desert Research Institute, 755 E. Flamingo Road, Las Vegas NV 89119, USA
| | - John A. Arnone
- Division of Earth and Ecosystem Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno NV 89512, USA
| | - Albin Hammerle
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA
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24
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Haslwanter A, Hammerle A, Wohlfahrt G. Open- vs. closed-path eddy covariance measurements of the net ecosystem carbon dioxide and water vapour exchange: a long-term perspective. AGRICULTURAL AND FOREST METEOROLOGY 2009; 149:291-302. [PMID: 24465069 PMCID: PMC3898020 DOI: 10.1016/j.agrformet.2008.08.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The differential design, deployment and data post-processing of open- (OP) and closed-path (CP) eddy covariance systems is a potential source of bias for ongoing global flux synthesis activities. Here we use a unique six year data set of concurrent CP and OP carbon dioxide (CO2) and water vapour (H2O) eddy covariance flux measurements above a temperate mountain grassland in Austria to explore the consequences of these differences on a long-term basis. The theoretically based transfer function approach was able to account and correct for the differences in low-pass filtering between the two systems. Corrected CO2 and H2O fluxes exhibited excellent 1:1 correspondence, but the CP system tended to underestimate OP H2O fluxes during conditions of high air temperature, wind speed and global radiation, large sun angles and low relative humidity. Corrections for self-heating of the OP infra-red gas analyser had a very small effect on these relationships. Energy balance closure was slightly more favourable for the OP system. No significant differences were found for the random flux uncertainty of both systems. A larger fraction of OP data had to be excluded because of obstructions of the infra-red path by water and snow. This, however, did not translate into a correspondingly larger fraction of accepted CP flux values, because of a larger percentage of CP flux data failing on the stationarity test. Integrated over the annual cycle, the CP system yielded on average a more positive net ecosystem CO2 exchange (25 vs. 0 gC m-2 y-1) and a lower evapotranspiration (465 vs. 549 mm y-1) as compared to the OP system.
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Affiliation(s)
- Alois Haslwanter
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
| | - Albin Hammerle
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
| | - Georg Wohlfahrt
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
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25
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Wohlfahrt G, Hammerle A, Haslwanter A, Bahn M, Tappeiner U, Cernusca A. Disentangling leaf area and environmental effects on the response of the net ecosystem CO 2 exchange to diffuse radiation. GEOPHYSICAL RESEARCH LETTERS 2008; 35:L16805. [PMID: 24347740 PMCID: PMC3858830 DOI: 10.1029/2008gl035090] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
There is an ongoing discussion about why the net ecosystem CO2 exchange (NEE) of some ecosystems is less sensitive to diffuse radiation than others and about the role other environmental factors play in determining the response of NEE to diffuse radiation. Using a six-year data set from a temperate mountain grassland in Austria we show that differences between ecosystems may be reconciled based on their green area index (GAI; square meter green plant area per square meter ground area) - the sensitivity to diffuse radiation increasing with GAI. Our data suggest diffuse radiation to have a negligible influence on NEE below a GAI of 2 m2 m-2. Changes in air/soil temperature and air humidity concurrent with the fraction of diffuse radiation were found to amplify the sensitivity of the investigated temperate mountain grassland ecosystem to diffuse radiation.
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Affiliation(s)
- Georg Wohlfahrt
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
| | - Albin Hammerle
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
| | - Alois Haslwanter
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
| | - Michael Bahn
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
| | - Ulrike Tappeiner
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
| | - Alexander Cernusca
- Institut für Ökologie, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria
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