Fine-Root Ecology Database (FRED)

To address the need for a centralized root trait database, available to empiricists and modelers alike, we are compiling FRED from published literature and unpublished data. FRED currently houses more than 16,000 observations of structural and functional root traits and their associated site, vegetation, edaphic, and climatic conditions from across the globe. Data collection is ongoing and will continue for the foreseeable future. Preliminary glimpses from FRED indicate that data are available for model improvement…but also that more data are needed. Join the conversation at: http://roots.ornl.gov.

Collaborators: A. Shafer Powell, M. Luke McCormack

Community Root Module (CRM)

We are working to develop a modularized version of the ACME Land Model to make models more accessible to the boarder community of rhizosphere ecologists.

Collaborators: Dali Wang, Yang Xu, Jeff Warren, Anthony Walker

Fine-root and fungal dynamics in SPRUCE: 2012 - on-going

Manual minirhizotrons, along with newly-developed automated minirhizotrons, were installed in each SPRUCE experimental plot in fall, 2012. The manual minirhizotrons are being used to track the responses of fine-root dynamics to warming and elevated [CO₂] over the next 10 years. The high-magnification and automated nature of the new minirhizotron systems from RhizoSystems, LLC, will allow us to track changes in root dynamics, as well as fungal hyphae, at much higher temporal resolution.

Collaborators: John Latimer, Joanne Childs

Plant-available nutrients in SPRUCE: 2013 - on-going

Several methods are being used to track changes in plant-available NH₄-N, NO₃-N, and PO₄ in response to warming and elevated [CO₂] over the next 10 years. We deployed WECSA ion-exchange resins across hummock-hollow microtopography in two locations in each SPRUCE plot, and resins are retrieved every 28 days during the growing season to determine an integrated measure of root-available nutrients.

Collaborators: John Latimer, Joanne Childs, Deanne Brice, Holly Vander Stel

Root ingrowth cores in SPRUCE:
2014 - on-going

Given the difficulty of distinguishing between living and dead roots in the anaerobic bog environment, root ingrowth cores constructed of rigid polypropylene tubes and filled with commercial peat from a nearby bog are being used to capture newly-grown roots. Ingrowth cores have been harvested seasonally from paired hummock-hollow microtopography in two locations in each SPRUCE plot. Cores are sectioned into 10-cm increments, and spruce, larch, and shrub roots are removed and analyzed by functional class for mass, morphology, and chemistry (using jewelers glasses to see shrub roots that are finer than a human hair!).

Collaborators: Deanne Brice, Joanne Childs, Holly Vander Stel

Initial root, peat characteristics in  SPRUCE:
2012

Initial root biomass distribution (along with peat characteristics and chemsitry) was determined prior to initiation of experimental treatments by taking 3-m deep soil cores in hummock-hollow microtopography in each SPRUCE experimental plot in August, 2012. Cores were sectioned into 10-cm or larger increments, and spruce, larch, and shrub roots were removed (using jewelers glasses to see shrub roots finer than a human hair!).

Iversen CM, Hanson PJ, Brice DJ, Phillips JR, McFarlane KJ,  Hobbie EA, Kolka RK. 2014. SPRUCE Peat Physical and Chemical Characteristics from Experimental Plot Cores, 2012. Carbon  Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, OakRidge, TN, USA. http://dx.doi.org/10.3334/CDIAC/spruce.005.

Fine-root dynamics in a bog:
2011 - 2012
Few experiments have investigated fine-root dynamics in wetland ecosystems. Prior to the SPRUCE experiment, we installed minirhizotrons in an ombrotrophic bog ecosystem in northern MN, USA across gradients of black spruce density and hummock-hollow microtopography, and quantified root growth and mortality every week. Data are being used to inform a future climatic and environmental change manipulation on-site, and will add to our limited knowledge of rooting dynamics in peatland ecosystems.

Iversen CM, Childs J, Norby RJ, Ontl TA, Kolka RK, Brice DJ, McFarlane K, Hanson PJ. Just beneath the surface: The distribution and dynamics of fine roots in an ombrotrophic bog. In preparation.

Advancing the use of minirhizotrons in wetlands

Together with an international group of experts, we developed a consensus on, and a methodological framework for, the appropriate installation and use of minirhizotrons in wetlands.

Iversen CM, Murphy MT, Allen ME, Childs J, Eissenstat DM, Lilleskov EA, Sarjala TM, Sloan VL, Sullivan PF (2012). Advancing the use of minirhizotrons in wetlands. Plant and Soil 352: 23-39. [pdf]

See an ORNL press release on this paper, and associated news coverage at knoxnews.com and sciencedaily.com.

Capturing the variation in plant traits across Arctic tundra: on-going research

One of the five main tasks in Phase 2 will be to understand how warming and permafrost thaw will affect above- and belowground plant functional traits, and what the consequences might be for Arctic ecosystem carbon, energy, water, and nutrient fluxes. This work will be conducted across gradients of polygonal tundra in Barrow, AK, as well as in a more southerly site near Nome, AK, on the Seward Peninsula. 

Collaborators: A Breen, E Euskirchen, A Rogers, S Serbin, P Thornton, SD Wullschleger, C Xu , F Yuan

Differentiating arctic PFTs based on root nitrogen aquisition: on-going research

In July, 2013, we injected a ¹⁵N tracer into the rooting zone at three targeted depth intervals (organic layer, mineral soil, and the permafrost boundary) in order to characterize nitrogen acquisition for species representing three important plant functional types (PFTs) on the Barrow Ecological Observatory. The amount of nitrogen acquired from different depths throughout the soil profile is being used to refine definitions of plant functional types in arctic models.

Collaborators: J Childs, JA Liebig, RJ Norby, IJ Slette, VL Sloan, HM Vander Stel; SD Wullschleger

Carbon and nutrient release from an organic-rich active layer across a gradient of polygonal tundra: on-going research

Using soil cores collected in summer, 2012 in Barrow, AK, we simulated future temperatures in a soil incubation study to investigate the effects of warming on soil carbon and nutrient mineralization.

Iversen CM, Vander Stel HM, Norby RJ, Sloan VL, Childs J, Brice DJ, Keller JK, Jong A, Ladd MP, Wullschleger SD. 2015. Active Layer Soil Carbon and Nutrient Mineralization, Barrow, Alaska, 2012.Next Generation Ecosystem Experiments Arctic Data Collection, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA. Data set accessed at http://dx.doi.org/10.5440/1185213.

Treat CC, Natali SM, Ernakovich J, Iversen CM, Lupascu M, McGuire AD, Norby RJ, Chowdhury TR, Richter A, Santruckova H, Schädel C, Schuur EAG, Sloan VL, Turetsy MR, Waldrop MP. 2015. A pan-Arctic synthesis of CH₄ and CO₂ production from anoxic soil incubations. Global Change Biology 21: 2787-2803. doi: 10.1111/gcb.12875.

Plant community dynamics across a gradient of polygonal tundra: on-going research

In 2012 and 2013, we investigated the relationships among plant community composition, above- and belowground biomass and N content, and edaphic and environmental conditions, and how these relationships changed across a gradient of polygonal tundra in Barrow, AK.

Sloan VL, Brooks JD, Wood SJ, Liebig JA, Siegrist J, Iversen CM, Norby RJ. 2014. Plant community composition and vegetation height, Barrow, Alaska, Ver. 1. Next Generation Ecosystem Experiments Arctic Data Collection, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA. Data set accessed at http://dx.doi.org/10.5440/1129476.

Sloan VL, Liebig JA, Hahn MS, Curtis JB, Brooks JD, Rogers A, Iversen CM, Norby RJ. 2014. Soil temperature, soil moisture and thaw depth, Barrow, Alaska, Ver. 1. Next Generation Ecosystem Experiments Arctic Data Collection, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA. Data setaccessed at http://dx.doi.org/10.5440.1121134.

Sloan VL, Iversen CM, Liebig JA, Curtis JB, Hahn MS, Siegrist J, Norby RJ. 2014. Plant Available Nutrients, Barrow, Alaska Ver. 1. Next Generation Ecosystem Experiments Arctic Data Collection, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge,Tennessee, USA. Data set accessed at http://dx.doi.org/10.5440/1120920.

Photo credit: J Brooks

Belowground carbon partitioning in historical FACE experiment: on-going research
In summer 2011, we returned to the site of a historical Free-Air CO2-enrichment (FACE) experiment in a sweetgum plantation. We girdled one-half of the trees in each treatment plot with goals of determining the effects of tree carbon inputs on soil carbon and nutrient cycling, and quantifying the size of belowground carbon storage pools.

Collaborators: J Childs, CT Garten, RJ Norby, JM Warren

Lynch DJ, Matamala R, Iversen CM, Norby RJ, Gonzalez-Meler MA. 2013. Stored carbon partly fuels fine-root respiration but is not used for production of new fine roots. New Phytologist 199: 420-430. [pdf]

See news coverage of our excellent student interns on a local TV station.

Photo credit: R. Norby

Carbon partitioning in a young loblolly pine
 
Our objective was to improve the carbon partitioning routines in existing ecosystem models, and test the models using short-term, comprehensive field measurements of processes related to carbon partitioning from leaves to roots and roots to soil.

Warren JM, Iversen CM, Garten CT, Norby RJ, Childs J, Brice DJ, Evans RM, Gu L, Thornton PE, Weston DJ (2012). Timing and magnitude of carbon partitioning through a young loblolly pine (Pinus taeda L.) stand using 13C labeling and shade treatments. Tree Physiology 32: 799-813. [pdf]

Belowground harvest: on-going research
We excavated two large soil pits by hand in each treatment ring in late June, 2009. Roots were separated into diameter classes for biomass and nutrient analyses. Subsamples of sieved soil were used in a soil incubation experiment to determine carbon and nitrogen mineralization throughout the soil profile.

Iversen CM, Keller JK, Garten CT, Norby RJ (2012). Soil carbon and nitrogen cycling and storage throughout the soil profile in a sweetgum plantation after 11 years of CO2-enrichment. Global Change Biology 18: 1684-1697. [pdf]

Plant and soil samples have been archived and are available to the scientific community upon request.

Root decomposition and carbon storage in soil organic matter: on-going research
We combined root decomposition techniques with soil fractionation techniques to quantify the transfer of carbon and nitrogen from decomposing fine-root litter to relatively long-lived SOM using the unique depleted C-13 signature of organic material in plants and soils enriched with elevated [CO2]. We hypothesized that increased root quantity and decreased root quality under elevated [CO2] would increase carbon and nitrogen storage in soil organic matter. This research was funded by a dissertation improvement grant from the National Science Foundation.

Collaborators: JD Jastrow, RJ Norby

Nitrogen cycling throughout the soil profile under elevated [CO2]
We used isotope pool dilution to measure potential gross nitrogen cycling rates throughout the soil profile. We found that nitrogen mineralization at depth in the soil, combined with increased root exploration of the soil volume under elevated [CO2], may be more important than changes in potential gross nitrogen cycling rates in sustaining forest responses to rising atmospheric CO2.

Iversen CM, Hooker TD, Classen AT, Norby RJ (2011). Net mineralization of N at deeper soil depths as a potential mechanism for sustained forest production under elevated [CO2]. Global Change Biology 17: 1130-1139. [pdf]

Digging deeper: Rooting distributions in CO2- enriched forests
Experimental evidence from a diverse set of forested ecosystems indicates that CO2-enrichment may lead to deeper rooting distributions. Altered rooting distributions are expected to affect important ecosystem processes such as root physiology and soil nutrient cycling. However, the causes of greater root production at deeper soil depths under elevated [CO2] require further investigation. Progress in understanding and modeling the interface between deeper rooting distributions and soil nutrient cycling will be critical in projecting the sustainability of forest responses to rising atmospheric [CO2].

Iversen CM (2010). Digging deeper: Fine root responses to rising atmospheric [CO2] in forested ecosystems. New Phytologist 186: 346-357. This paper was a finalist in the New Phytologist Tansley Medal competition. [pdf]

Missing links in the root-SOM continuum
Our goal was to synthesize root- and soil-centric studies into an integrated understanding of belowground ecosystem processes in an organized oral session at an annual ESA meeting. Speakers emphasized the importance of the rhizosphere and soil environment for the transformation of root-derived carbon to long-lived SOM. Integration of observations made along the root-SOM continuum can lead to a more holistic view of belowground ecology.

Iversen CM, O’Brien SL (2010). Organized Oral Session 3. Missing links in the root–soil organic matter continuum. Bulletin of the Ecological Society of America 91: 54-64. [pdf]

O ’Brien SL, Iversen CM (2009). Missing links in the root-soil organic matter continuum. New Phytologist 184: 513-516. [pdf]

Root-derived carbon and nitrogen input to the soil
We combined a long-term minirhizotron data set with continuous, root-specific measurements to assess carbon and nitrogen input from root mortality. We found that the flux of carbon and nitrogen into the soil nearly doubled under elevated [CO2] due to stimulated root production and mortality. Moreover, much of the carbon and nitrogen input occurred relatively deep in the soil profile where decomposition dynamics are likely to be different from what is commonly observed and modeled in the upper soil.

Iversen CM, Ledford J, Norby RJ (2008). CO2 enrichment increases carbon and nitrogen input from fine roots in a deciduous forest. New Phytologist: 179: 837-847. [pdf]

Nitrogen limitation controls carbon partitioning under elevated atmospheric [CO2]
In a nitrogen fertilization experiment in an adjacent sweetgum stand, we found that the increased production of ephemeral roots under elevated [CO2] was most likely a mechanism for greater nitrogen acquisition in response to nitrogen limitation within the stand. In turn, the increased production of fine roots with a relatively large nitrogen concentration necessitated increased nitrogen uptake from the soil. 

Iversen CM, Norby RJ (2008). Nitrogen limitation in a sweetgum plantation: Implications for carbon allocation and storage. Canadian Journal of Forest Research 38: 1021-1032. [pdf]

Photo credit: J. Childs

Fine-root dynamics in a constructed old-field
We combined a long-term minirhizotron data set with continuous, root-specific measurements to assess root biomass production and mortality in a constructed old-field ecosystem exposed to elevated [CO2], warming, and drought conditions. We asked whether multiple atmospheric and climatic factors would interact to influence root production and turnover throughout the soil profile.

Collaborators: J Childs, AT Classen, RJ Norby

Photo credit: S. Bridgham

Scaling plant nutrient use in peatland ecosystems
We fertilized a natural gradient of nutrient-limited peatland ecosystems in Michigan, USA, with nitrogen, phosphorus, or a combination of both nutrients. Our objectives were to determine how changes in carbon and nitrogen partitioning within a plant, and changes in community composition, would affect plant nitrogen-use efficiency. Plant nitrogen-use efficiency and its components differed from the leaf- to community level, and depended on nitrogen or phosphorus limitation.

Iversen CM, Bridgham SD, Kellogg LE (2010). Scaling plant nitrogen-use and uptake efficiencies in response to nutrient addition in peatlands. Ecology 91: 693-707. [pdf]