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A publications database showing the location of research associated with Toolik Field Station

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A publications database showing the location of research associated with Toolik Field Station

latest article added on February 2014

ArticleFirst AuthorPublished
Species compositional differences on different-aged glacial landscapes drive contrasting responses of tundra to nutrient addition.HOBBIE, SARAH E.2005

Species compositional differences on different-aged glacial landscapes drive contrasting responses of tundra to nutrient addition.

Keywords

Alaska;Arctic;Betula nana;fertilization;moist acidic tundra;moist non-acidic tundra;net primary production;nitrogen;pH;phosphorus

Abstract

  1. In the northern foothills of the Brooks Range, Alaska, moist non-acidic tundra dominates more recently deglaciated upland landscapes, whereas moist acidic tundra dominates older upland landscapes. In previous studies, experimental fertilization of moist acidic tussock tundra greatly increased the abundance and productivity of the deciduous dwarf shrub Betula nana. However, this species is largely absent from moist non-acidic tundra.
  2. These two common upland tundra community types exhibited markedly different responses to fertilization with nitrogen and phosphorus. In moist acidic tundra, cover of deciduous shrubs (primarily B. nana) increased after only 2 years, and by 4 years vascular biomass and above-ground net primary productivity (ANPP) had increased significantly, almost entirely because of Betula. In moist non-acidic tundra, both biomass and ANPP were again significantly greater, but no single species dominated the response to fertilization. Instead, the effect was due to a combination of several small, sometimes statistically non-significant responses by forbs, graminoids and prostrate deciduous shrubs.
  3. The different growth form and species' responses suggest that fertilization will cause carbon cycling through plant biomass to diverge in these two tundra ecosystems. Already, production of new stems by apical growth has increased relative to leaf production in acidic tundra, whereas the opposite has occurred in non-acidic tundra. Secondary stem growth has also increased as a component of primary production in acidic tundra, but is unchanged in non-acidic tundra. Thus, fertilization will probably increase carbon sequestration in woody biomass of B. nana in acidic tundra, while increasing carbon turnover (but not storage) of non-woody species in non-acidic tundra.
  4. These results indicate that nutrient enrichment can have very different consequences for plant communities that occur on different geological substrates, because of differences in composition, even though they share the same regional species pool. Although the specific edaphic factors that maintain compositional differences in this case are unknown, variation in soil pH and related variability in soil nutrient availability may well play a role.

Authors

HOBBIE, SARAH E.,GOUGH, LAURA,SHAVER, GAIUS R.

Year Published

2005

Publication

Journal of Ecology

Locations
DOI

10.1111/j.1365-2745.2005.01006.x

Plant and soil responses to neighbour removal and fertilization in Alaskan tussock tundra.BRET-HARTE, M. SYNDONIA2004

Plant and soil responses to neighbour removal and fertilization in Alaskan tussock tundra.

Keywords

nitrogen;phosphorus;plant functional types;soil nutrient availability;species interactions

Abstract

  1. Species interactions will probably be important in determining plant community structure as availability of soil nutrients changes due to climate warming or anthropogenic N deposition. We removed dominant species, combinations of species, and entire plant functional types, in fertilized and unfertilized plots in tussock tundra.
  2. After 2 years, graminoids responded more strongly to fertilizer than other growth forms, and the responses of graminoids and deciduous shrubs to fertilizer were greater under neighbour removal than in the intact community. Deciduous shrubs, evergreen shrubs and graminoids increased their biomass with fertilization, whereas non-vascular plants decreased.
  3. Dominant species from each growth form usually responded strongly to fertilization, but half of all subdominant species responded weakly or not at all. Few species responded to neighbour removal.
  4. Soil nutrient availability, however, was elevated significantly by both fertilization and neighbour removal. Neighbour removal increased nutrient availability in fertilized plots by up to two orders of magnitude, and availability of and in some unfertilized removal treatments was greater than in the fertilized intact community.
  5. The failure of many plant species to respond with enhanced growth to soil nutrients made available by neighbour removal, despite their response to fertilization, could be due to (i) tundra plants having such rigid niche complementarity that they are unable to utilize these additional resources, or (ii) insufficient time having elapsed for the remaining species to respond, because nutrients derived from neighbour removal probably became available later than nutrients added as fertilizer.
  6. There may be a high potential for loss of available nutrients from the tundra ecosystem when species composition changes, if the remaining plants cannot adjust to use nutrients made available by the loss of their neighbours.

Authors

BRET-HARTE, M. SYNDONIA,GARCÍA, ERICA A.,SACRÉ, VINCIANE M.,WHORLEY, JOSHUA R.,WAGNER, JOANNA L.,LIPPERT, SUZANNE C.,CHAPIN, F. STUART

Year Published

2004

Publication

Journal of Ecology

Locations
DOI

10.1111/j.0022-0477.2004.00902.x

VARIATION IN DISSOLVED ORGANIC MATTER CONTROLS BACTERIAL PRODUCTION AND COMMUNITY COMPOSITION.Judd, Kristin E.2006

VARIATION IN DISSOLVED ORGANIC MATTER CONTROLS BACTERIAL PRODUCTION AND COMMUNITY COMPOSITION.

Keywords

bacterial community composition;DGGE;DOC;DOM bioavailability;ecosystem;landscape;terrestrial DOM

Abstract

An ongoing debate in ecology revolves around how species composition and ecosystem function are related. To address the mechanistic controls of this relationship, we manipulated the composition of dissolved organic matter (DOM) fed to aquatic bacteria to determine effects on both bacterial activity and community composition. Sites along terrestrial to aquatic flow paths were chosen to simulate movement of DOM through catchments, and DOM was fed to downslope and control bacterial communities. Bacterial production was measured, and DOM chemistry and bacterial community composition (using denaturing gradient gel electrophoresis of 16S rRNA genes) were characterized following incubations. Bacterial production, dissolved organic carbon (DOC)-specific bacterial production, and DOC consumption were greatest in mesocosms fed soil water DOM; soil water DOM enhanced lake and stream bacterial production by 320–670% relative to lake and stream controls. Stream DOM added to lake bacteria depressed bacterial production relative to lake controls in the early season (−78%) but not the mid-season experiment. Addition of upslope DOM to stream and lake bacterial communities resulted in significant changes in bacterial community composition relative to controls. In four of five DOM treatments, the bacterial community composition converged to the DOM source community regardless of the initial inoculum. These results demonstrate that shifts in the supply of natural DOM were followed by changes in both bacterial production and community composition, suggesting that changes in function are likely predicated on at least an initial change in the community composition. The results indicate that variation in DOM composition of soil and surface waters influences bacterial community dynamics and controls rates of carbon processing in set patterns across the landscape.

Authors

Judd, Kristin E., Byron C. Crump, and George W. Kling.

Year Published

2006

Publication

Ecology

Locations
DOI

10.1890/0012-9658(2006)87[2068:VIDOMC]2.0.CO;2

This article contributed by:

Ecological Society of America

MICROBIAL COMMUNITY COMPOSITION AND FUNCTION ACROSS AN ARCTIC TUNDRA LANDSCAPE.Zak, Donald R.2006

MICROBIAL COMMUNITY COMPOSITION AND FUNCTION ACROSS AN ARCTIC TUNDRA LANDSCAPE.

Keywords

arctic tundra;13C tracers;dissolved organic carbon;extracellular enzymes;landscape patterns;microbial communities

Abstract

Arctic landscapes are characterized by a diversity of ecosystems, which differ in plant species composition, litter biochemistry, and biogeochemical cycling rates. Tundra ecosystems differing in plant composition should contain compositionally and functionally distinct microbial communities that differentially transform dissolved organic matter as it moves downslope from dry, upland to wet, lowland tundra. To test this idea, we studied soil microbial communities in upland tussock, stream-side birch–willow, and lakeside wet sedge tundra in arctic Alaska, USA. These are a series of ecosystems that differ in topographic position, plant composition, and soil drainage. Phospholipid fatty acid (PLFA) analyses, coupled with compound-specific 13C isotope tracing, were used to quantify microbial community composition and function; we also assayed the activity of extracellular enzymes involved in cellulose, chitin, and lignin degradation. Surface soil from each tundra ecosystem was labeled with 13C-cellobiose,13C-N-acetylglucosamine, or 13C-vanillin. After a five-day incubation, we followed the movement of 13C into bacterial and fungal PLFAs, microbial respiration, dissolved organic carbon, and soil organic matter. Microbial community composition and function were distinct among tundra ecosystems, with tussock tundra containing a significantly greater abundance and activity of soil fungi. Although the majority of 13C-labeled substrates rapidly moved into soil organic matter in all tundra soils (i.e., 50–90% of applied 13C), microbial respiration of labeled substrates in wet sedge tundra soil was lower than in tussock and birch–willow tundra; ̃ 8% of 13C-cellobiose and ̃5% of 13C-vanillin was respired in wet sedge soil vs. 26–38% of 13C-cellobiose and 18–21% of 13C-vanillin in the other tundra ecosystems. Despite these differences, wet sedge tundra exhibited the greatest extracellular enzyme activity. Topographic variation in plant litter biochemistry and soil drainage shape the metabolic capability of soil microbial communities, which, in turn, influence the chemical composition of dissolved organic matter across the arctic tundra landscape.

Authors

Zak, Donald R., and George W. Kling.

Year Published

2006

Publication

Ecology

Locations
DOI

10.1890/0012-9658(2006)87[1659:MCCAFA]2.0.CO;2

This article contributed by:

Ecological Society of America

Seasonal patterns of carbon dioxide and water fluxes in three representative tundra ecosystems in northern AlaskaEuskirchen, E. S.2012

Seasonal patterns of carbon dioxide and water fluxes in three representative tundra ecosystems in northern Alaska

Keywords

Arctic tundra, ecosystem respiration, eddy covariance, evapotranspiration, gross primary production, net ecosystem exchange, water balance, water use efficiency

Abstract

Understanding the carbon dioxide and water fluxes in the Arctic is essential for accurate assessment and prediction of the responses of these ecosystems to climate change. In the Arctic, there have been relatively few studies of net CO2, water, and energy exchange using micrometeorological methods due to the difficulty of performing these measurements in cold, remote regions. When these measurements are performed, they are usually collected only during the short summer growing season. We established eddy covariance flux towers in three representative Alaska tundra ecosystems (heath tundra, tussock tundra, and wet sedge tundra), and have collected CO2, water, and energy flux data continuously for over three years (September 2007–May 2011). In all ecosystems, peak CO2 uptake occurred during July, with accumulations of 51–95 g C/m2 during June–August. The timing of the switch from CO2 source to sink in the spring appears to be regulated by the number of growing degree days early in the season, indicating that warmer springs may promote increased net CO2 uptake. However, this increased uptake in the spring may be lost through warmer temperatures in the late growing season that promote respiration, if this respiration is not impeded by large amounts of precipitation or cooler temperatures. Net CO2 accumulation during the growing season was generally lost through respiration during the snow covered months of September–May, turning the ecosystems into net sources of CO2 over measurement period. The water balance from June to August at the three ecosystems was variable, with the most variability observed in the heath tundra, and the least in the tussock tundra. These findings underline the importance of collecting data over the full annual cycle and across multiple types of tundra ecosystems in order to come to a more complete understanding of CO2 and water fluxes in the Arctic.

Authors

Euskirchen, E. S., Bret-Harte, M. S., Scott, G. J., Edgar, C and Shaver, G. R.

Year Published

2012

Publication

Ecosphere

Locations
DOI

10.1890/ES11-00202.1

This article contributed by:

Ecological Society of America

ENVIRONMENTAL-EFFECTS ON CO-2 EFFLUX FROM WATER TRACK AND TUSSOCK TUNDRA IN ARCTIC ALASKA, USAOBERBAUER, SF1991

ENVIRONMENTAL-EFFECTS ON CO-2 EFFLUX FROM WATER TRACK AND TUSSOCK TUNDRA IN ARCTIC ALASKA, USA

Keywords

SRBD

Abstract

CO2 efflux and variation in soil environmental characteristics were examined in two tundra vegetation communities, water track (a small drainage of intermittent water flow) and tussock tundra, in the northern foothills of the Philip Smith Mountains in arctic Alaska. Correlation analyses were performed on the observations made at six times during the growing season in order to evaluate the relationships between system CO2 loss and soil moisture, soil temperature, depth of thaw, and depth to the water table. The two sites differed significantly in terms of soil moisture, soil temperature, depth of thaw, and water table depth on several of the sampling dates. During four of the six measurement periods, the rate of CO2 efflux differed significantly between sites. Early in the season, respiration was greater in tussock tundra than at the water track, but later in the season, rates at the water track exceeded those at the tussock site. Highest rates were measured at the water track near mid-season. Efflux of CO2 at both sites was positively correlated with soil temperature. Soil surface (0-5 cm depth) environmental conditions were better predictors of CO2 efflux than were conditions measured at greater depth (5-10 cm). Soil moisture appeared to increase respiration between 100 and 700% of soil dry weight and decrease soil respiration at higher water contents. The effects of soil moisture were stronger in tussock tundra than in the water track community. These data suggest that both soil temperature and soil moisture limit CO2 efflux in water track and tussock tundra communities and that the relative importance of these factors changes throughout the growing season.

Authors

OBERBAUER, SF; TENHUNEN, JD; REYNOLDS, JF

Year Published

1991

Publication

ARCTIC AND ALPINE RESEARCH

Locations
DOI

10.2307/1551380

This article contributed by:

Global Database of Soil Respiration Data, Version 3.0. B.P. Lamberty and A.M. Thompson. 2014. Oak Ridge National Laboratory

ENVIRONMENTAL-EFFECTS ON CO2 EFFLUX FROM RIPARIAN TUNDRA IN THE NORTHERN FOOTHILLS OF THE BROOKS RANGE, ALASKA, USAOBERBAUER, SF1992

ENVIRONMENTAL-EFFECTS ON CO2 EFFLUX FROM RIPARIAN TUNDRA IN THE NORTHERN FOOTHILLS OF THE BROOKS RANGE, ALASKA, USA

Keywords

SRBD

Abstract

Carbon dioxide efflux and soil microenvironmental factors were measured diurnally in Carex aquatilus- and Eriophorum angustifolium-dominated riparian tundra communities to determine the relative importance of soil environmental factors controlling ecosystem carbon dioxide exchange with the atmosphere. Measurements were made weekly between 18 June and 24 July 1990. Diurnal patterns in carbon dioxide efflux were best explained by changes in soil temperature, while seasonal changes in efflux were correlated with changes in depth to water table, depth to frozen soil and soil moisture. Carbon dioxide efflux rates were lowest early in the growing season when high water tables and low soil temperatures limited microbial and root activity. Individual rainfall events that raised the water table were found to strongly reduce carbon dioxide efflux. As the growing season progressed, rainfall was low and depth to water table and soil temperatures increased. In response, carbon dioxide efflux increased strongly, attaining rates late in the season of approximately 10 g CO2 m-2 day-1. These rates are as high as maxima recorded for other arctic sites. A mathematical model is developed which demonstrates that soil temperature and depth to water table may be used as efficient predictors of ecosystem CO2 efflux in this habitat. In parallel with the field measurements Of CO2 efflux, microbial respiration was studied in the laboratory as a function of temperature and water content. Estimates of microbial respiration per square meter under field conditions were made by adjusting for potential respiring soil volume as water table changed and using measured soil temperatures. The results indicate that the effect of these factors on microbial respiration may explain a large part of the diurnal and seasonal variation observed in CO2 efflux. As in coastal tundra sites, environmental changes that alter water table depth in riparian tundra communities will have large effects on ecosystem CO2 efflux and carbon balance.

Authors

OBERBAUER, SF; GILLESPIE, CT; CHENG, W; GEBAUER, R; SERRA, AS; TENHUNEN, JD

Year Published

1992

Publication

Oecologia

Locations
DOI

10.1007/BF00317851

This article contributed by:

Global Database of Soil Respiration Data, Version 3.0. B.P. Lamberty and A.M. Thompson. 2014. Oak Ridge National Laboratory

Sediment and nutrient delivery from thermokarst features in the foothills of the North Slope, Alaska: Potential impacts on headwater stream ecosystemsBowden, W. B.2008

Sediment and nutrient delivery from thermokarst features in the foothills of the North Slope, Alaska: Potential impacts on headwater stream ecosystems

Keywords

Toolik Field Station, thermokarst, Arctic, warming, climate change,

Abstract

Permafrost is a defining characteristic of the Arctic environment. However, climate warming is thawing permafrost in many areas leading to failures in soil structure called thermokarst. An extensive survey of a 600 km2 area in and around the Toolik Lake Natural Research Area (TLNRA) revealed at least 34 thermokarst features, two thirds of which were new since about 1980 when a high resolution aerial survey of the area was done. Most of these thermokarst features were associated with headwater streams or lakes. We have measured significantly increased sediment and nutrient loading from thermokarst features to streams in two well-studied locations near the TLNRA. One small thermokarst gully that formed in 2003 on the Toolik River in a 0.9 km2 subcatchment delivered more sediment to the river than is normally delivered in 18 years from 132 km2 in the adjacent upper Kuparuk River basin (a long-term monitoring reference site). Ammonium, nitrate, and phosphate concentrations downstream from a thermokarst feature on Imnavait Creek increased significantly compared to upstream reference concentrations and the increased concentrations persisted over the period of sampling (1999–2005). The downstream concentrations were similar to those we have used in a long-term experimental manipulation of the Kuparuk River and that have significantly altered the structure and function of that river. A subsampling of other thermokarst features from the extensive regional survey showed that concentrations of ammonium, nitrate, and phosphate were always higher downstream of the thermokarst features. Our previous research has shown that even minor increases in nutrient loading stimulate primary and secondary production. However, increased sediment loading could interfere with benthic communities and change the responses to increased nutrient delivery. Although the terrestrial area impacted by thermokarsts is limited, the aquatic habitat altered by these failures can be extensive. If warming in the Arctic foothills accelerates thermokarst formation, there may be substantial and wide-spread impacts on arctic stream ecosystems that are currently poorly understood.

Authors

Bowden, W. B., Gooseff, M. N., Balser, A., Green, A., Peterson, B. J. and Bradford, J.

Year Published

2008

Publication

Journal of Geophysical Research

Locations
DOI

10.1029/2007JG000470

This article contributed by:

Toolik Field Station, University of Alaska Fairbanks

Upscaling of CO 2 fluxes from heterogeneous tundra plant communities in Arctic Alaska Kade, Anja2012

Upscaling of CO 2 fluxes from heterogeneous tundra plant communities in Arctic Alaska

Keywords

Arctic tundra vegetation, chamber measurements, eddy covariance, net ecosystem carbon exchange, plant functional types

Abstract

We characterized the tundra vegetation at three eddy covariance towers located along a toposequence in northern Alaska and studied seasonal variations in plot-level CO2 fluxes among the dominant vegetation types with chambers during the summer and with the gradient-diffusion technique during the winter. We performed footprint analyses to determine the source areas contributing to the tower fluxes and scaled plot-level to eddy-covariance CO2 data based on the proportion of vegetation types occurring within the footprints. At peak growing season, both gross ecosystem exchange and ecosystem respiration were greater in moist acidic tussock tundra and wet sedge tundra than in dry heath tundra. This resulted in relatively similar values of net ecosystem exchange as measured by chambers in July in tussock tundra across all topographic positions and wet sedge tundra (−2.4 to −4.2 μmol CO2/m2/s) but low values in dry heath tundra (−0.4 μmol CO2/m2/s). Winter respiration was highest for tussock tundra in December, but there were no significant differences among vegetation types in February and April. Net and gross ecosystem exchange scaled up from summer chamber measurements compared well to tower data (r2 = 0.84 and r2 = 0.78, respectively), especially on level terrain, whereas plot-level CO2-flux measurements in the winter did not agree well with tower data. This is one of few studies to compare plot-level and tower fluxes during both summer and winter and to demonstrate successful upscaling of carbon exchange in Arctic tundra systems under certain conditions.

Authors

Kade, Anja, Bret-Harte, M. Syndonia, Euskirchen, Eugenie S., Edgar, Colin and Fulweber, Randy A.

Year Published

2012

Publication

Journal of Geophysical Research

Locations
DOI

10.1029/2012JG002065

Toolik Field Station begins year-round operationsAbels, M.2007

Toolik Field Station begins year-round operations

Keywords

Toolik Field Station

Abstract

No abstract available

Authors

Abels, M.

Year Published

2007

Publication

Witness the Arctic

Locations
This article contributed by:

Toolik Field Station, University of Alaska Fairbanks

Recent Articles

Seasonal Patterns of Carbon Dioxide and Water Fluxes in Three Representative Tundra Ecosystems in Northern Alaska

by Euskirchen, E. S., Bret-Harte, M. S., Scott, G. J., Edgar, C and Shaver, G. R.

Understanding the carbon dioxide and water fluxes in the Arctic is essential for accurate assessment and prediction of the responses of these ecosystems to climate change. In the Arctic, there have been relatively few studies of net CO2, water, and energy exchange using micrometeorological methods due to the difficulty of performing these measurements in cold, remote regions. When these measure...

published 2012 in Ecosphere

Upscaling of Co 2 Fluxes from Heterogeneous Tundra Plant Communities in Arctic Alaska

by Kade, Anja, Bret-Harte, M. Syndonia, Euskirchen, Eugenie S., Edgar, Colin and Fulweber, Randy A.

We characterized the tundra vegetation at three eddy covariance towers located along a toposequence in northern Alaska and studied seasonal variations in plot-level CO2 fluxes among the dominant vegetation types with chambers during the summer and with the gradient-diffusion technique during the winter. We performed footprint analyses to determine the source areas contributing to the tower flux...

published 2012 in Journal of Geophysical Research


Carbon Loss from an Unprecedented Arctic Tundra Wildfire

by Mack, Michelle C., Bret-Harte, M. Syndonia, Hollingsworth, Teresa N., Jandt, Randi R., Schuur, Edward A. G., Shaver, Gaius R. and Verbyla, David L.

Arctic tundra soils store large amounts of carbon (C) in organic soil layers hundreds to thousands of years old that insulate, and in some cases maintain, permafrost soils. Fire has been largely absent from most of this biome since the early Holocene epoch, but its frequency and extent are increasing, probably in response to climate warming. The effect of fires on the C balance of tundra landsc...

published 2011 in Nature

Sediment and Nutrient Delivery from Thermokarst Features in the Foothills of the North Slope, Alaska: Potential Impacts on Headwater Stream Ecosystems

by Bowden, W. B., Gooseff, M. N., Balser, A., Green, A., Peterson, B. J. and Bradford, J.

Permafrost is a defining characteristic of the Arctic environment. However, climate warming is thawing permafrost in many areas leading to failures in soil structure called thermokarst. An extensive survey of a 600 km2 area in and around the Toolik Lake Natural Research Area (TLNRA) revealed at least 34 thermokarst features, two thirds of which were new since about 1980 when a high resolution ...

published 2008 in Journal of Geophysical Research