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Harvard Forest Data Archive

HF278

Phenology and Carbon Allocation of Roots at Harvard Forest 2011-2013

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Data

Overview

  • Lead: Rose Abramoff, Adrien Finzi
  • Investigators:
  • Contact: Rose Abramoff
  • Start date: 2011
  • End date: 2013
  • Status: completed
  • Location: Prospect Hill Tract (Harvard Forest)
  • Latitude: +42.504361 to +42.54379083
  • Longitude: -72.199898 to -72.17676733
  • Elevation:
  • Taxa: Fraxinus americana (white ash), Quercus rubra (red oak), Tsuga canadensis (eastern hemlock)
  • Release date: 2019
  • Revisions:
  • EML file: knb-lter-hfr.278.3
  • DOI: digital object identifier
  • Related links:
  • Study type: short-term measurement
  • Research topic: soil carbon and nitrogen dynamics
  • LTER core area: primary production, organic matter
  • Keywords: biomass, carbohydrates, carbon, hemlock, nitrogen, oak, phenology, respiration, roots
  • Abstract:

    The objective of this study is to estimate the phenology and partitioning of C allocated belowground across the growing season at Harvard Forest in two hardwood stands dominated by Quercus rubra and Fraxinus americana, respectively, and one conifer stand dominated by Tsuga canadensis.

    The phenology of fine root production was characterized by multiple flushes of growth and mortality, especially in the red oak (Q. rubra) stand. Root exudation rate did not have a clear seasonal signal. The deciduous hardwood stands allocated C belowground earlier in the season compared to the conifer-dominated stand. Deciduous stands also allocated a greater proportion of total belowground C flux (TBCF) to root growth compared to the conifer-dominated hemlock (T. canadensis) stand. Of the three stands, red oak partitioned the greatest proportion of TBCF (~50%) to root growth, while hemlock partitioned the least.

  • Methods:

    Overview

    Plots were established in three mono-dominant stands: white ash, red oak, and eastern hemlock. We established 6 biometry plots per stand (N = 18) and 10 minirhizotron tube plots per stand (N = 30). The basal area in each 8-m-radius biometry plot is composed of 80% dominant tree species, with the inner 5-m area containing only the dominant species.

    Root biomass - minirhizotrons

    Root production and turnover were measured using a BTC-100x high magnification minirhizotron camera system (Bartz Technology Company, Carpenteria, CA). The camera system was inserted into cellulose acetate butyrate tubes installed at a 45° angle to a vertical soil depth of 40 cm. Thirteen tubes were installed in the center of each minirhizotron tube plot at Harvard Forest 10+ years ago (n = 4 in red oak, n = 9 in eastern hemlock). Seventeen tubes were installed in November 2012 (n = 6 in red oak, n = 1 in eastern hemlock, and n = 10 in white ash) for a sample size of n = 10 for each stand in 2013 and 2014.

    Minirhizotron tubes installed in November 2012 likely severed existing roots during placement and may have increased root growth rates in the following seasons. We detected a measurable but transient effect of tube installation on root production in red oak. There was no detectable installation effect on red oak root mortality or on the single hemlock tube installed. All white ash tubes were newly installed in November 2012 so it was not possible to establish an effect of installation on white ash root production.

    The minirhizotron camera captures thirty-nine sequential images that are 13.5 x 17 mm in size along the upper axis of each tube at each sampling interval. The resulting images were processed using the open source imaging software Rootfly (Rootfly Development Team, Version 2.0.2, GNU General Public License). Root length and diameter were scaled to mass using a site-specific relationship based on n = 20 fine root (diameter less than 2 mm) segments per species. Root biomass was estimated from the images using the method of Taylor et al. (2014).

    Root biomass – soil cores

    Each month, we collected three 10 x 10 cm samples of the organic horizon and three 4.7 cm diameter mineral soil samples to a depth of 15 cm in each plot. Roots were removed and sorted into fine (less than 2 mm), coarse (greater than 2 mm), live and dead pools. Sorted roots were dried and weighed to obtain standing biomass. Subsamples of roots from monthly soil coring were assayed for carbon and nitrogen content using an elemental analyzer (model NC2500; CE Instruments, Milan, Italy). Fine root standing biomass for the organic horizon down to a depth of 15 cm in the mineral soil was scaled up to g C m-2 by adjusting for the horizontal area of the soil core, the carbon content of roots in each stand, and rock content.

    Nonstructural carbohydrates

    We collected three ~1–2 g fine root samples from each biometry plot. Roots were excavated, washed, and frozen in liquid nitrogen until analysis. Sugars were extracted from dried and finely ground root tissue using a 12:5:3 methanol:chloroform:water solution before being developed with 2% phenol and concentrated sulfuric acid. Absorbance was measured at 490 nm using a digital spectrophotometer (Spectronic 20D+, Thermo Scientific). Starch was extracted using a 0.005 N sulfuric acid solution at 95ºC and developed as described above.

    Root exudation

    Root exudates were collected from six fine root systems per stand in June and August 2012, and April, May, July and October 2013 following the method of Phillips et al. (2008, 2011). In brief, roots were excavated 48 hours prior to collection, washed, and incubated in a moist soil-sand mixture. Roots were placed into cuvettes with glass beads and a C-free nutrient solution 24 hours prior to collection. At the time of collection, exudate-containing nutrient solution was extracted with two additional flushes of C-free nutrient solution to ensure that exudates adhering to glass beads were flushed into solution. Samples were transported back to the lab on ice and analyzed for non-purgeable organic carbon content using an elemental analyzer (Shimadzu TOC-VCSH analyzer, New Haven, CT).

    Root respiration

    CO2 efflux was measured directly on recently severed fine roots, in the field at ambient temperature, using an infrared gas analyzer (LI6400; LiCor Biosciences). We compared respiration measurements of an attached and severed root system for each stand on three separate days and confirmed that respiration rates were similar between the two types of roots (correlation coefficient = 0.78) and stable up to approximately 7 hours.

    References

    Phillips, R. P., Y. Erlitz, R. Bier, and E. S. Bernhardt. 2008. New approach for capturing soluble root exudates in forest soils. Functional Ecology 22:990–999.

    Phillips, R. P., A. C. Finzi, and E. S. Bernhardt. 2011. Enhanced root exudation induces microbial feedbacks to N cycling in a pine forest under long-term CO2 fumigation. Ecology letters 14:187–94.

    Taylor, B. N., K. V. Beidler, A. E. Strand, and S. G. Pritchard. 2014. Improved scaling of minirhizotron data using an empirically-derived depth of field and correcting for the underestimation of root diameters. Plant and Soil 374:941–948.

  • Use:

    This dataset is released to the public under Creative Commons license CC BY (Attribution). Please keep the designated contact person informed of any plans to use the dataset. Consultation or collaboration with the original investigators is strongly encouraged. Publications and data products that make use of the dataset must include proper acknowledgement.

  • Citation:

    Abramoff R, Finzi A. 2019. Phenology and Carbon Allocation of Roots at Harvard Forest 2011-2013. Harvard Forest Data Archive: HF278.

Detailed Metadata

hf278-01: root biomass - soil cores

  1. date: sampling date
  2. species: dominant tree species where the sample was collected
    • FRAM: Fraxinus americana
    • QURU: Quercus rubra
    • TSCA: Tsuga canadensis
  3. plot: plot number
  4. ld: whether roots were live or dead
    • live: live
    • dead: dead
  5. fc: whether roots were fine or coarse
    • fine: diameter < 2mm
    • coarse: diameter > 2mm
  6. om: whether organic horizon or mineral soil
    • organic: organic horizon
    • mineral: mineral soil
  7. biomass: dry mass of roots, total mass of 3 combined cores (unit: gram / missing value: NA)
  8. biomass.g.m2: mass of roots per surface area, down to 15 cm depth (unit: gramsPerSquareMeter / missing value: NA)

hf278-02: root biomass - minirhizotrons

  1. date: date of image collection
  2. species: dominant tree species where the minirizhotron tube is located
    • FRAM: Fraxinus americana
    • QURU: Quercus rubra
    • TSCA: Tsuga canadensis
  3. tube: minirizhotron tube number
  4. biomass: mass of roots visible per tube, down to 15 cm depth (unit: gram / missing value: NA)
  5. biomass.g.m2: mass of roots per surface area, down to 15 cm depth (unit: gramsPerSquareMeter / missing value: NA)

hf278-03: root exudation

  1. species: dominant tree species where the sample was collected
    • FRAM: Fraxinus americana
    • QURU: Quercus rubra
    • TSCA: Tsuga canadensis
  2. plot: plot number
  3. date: sampling date
  4. mean.conc.mg.l: mean DOC concentration (unit: milligramsPerLiter / missing value: NA)
  5. cv.conc: coefficient of variation of the concentration trials (usually 3) (unit: dimensionless / missing value: NA)
  6. vol.ml: volume of exudate sample (unit: milliliter / missing value: NA)
  7. dw.g: dry weight of the root sample (unit: gram / missing value: NA)
  8. adj.conc.mg.l: adjusted DOC concentration (control DOC concentration substracted) (unit: milligramsPerLiter / missing value: NA)
  9. gcgr: mass of carbon exuded by root mass (unit: gram / missing value: NA)

hf278-04: root carbon and nitrogen content

  1. species: dominant tree species where the sample was collected
    • FRAM: Fraxinus americana
    • QURU: Quercus rubra
    • TSCA: Tsuga canadensis
  2. plot: plot number
  3. month: month of sample collection
  4. ld: whether roots were live or dead
    • L: live
    • D: dead
  5. fc: whether roots were fine or coarse
    • F: diameter < 2mm
    • C: diameter > 2mm
  6. n.per: root nitrogen content (%N) (unit: dimensionless / missing value: NA)
  7. c.per: root carbon content (%C) (unit: dimensionless / missing value: NA)
  8. c.n: carbon to nitrogen ratio (unit: dimensionless / missing value: NA)

hf278-05: nonstructural carbohydrates

  1. date: sampling date
  2. species: dominant tree species where the sample was collected
    • FRAM: Fraxinus americana
    • QURU: Quercus rubra
    • TSCA: Tsuga canadensis
  3. su.st: whether sugars or starch sample
    • starch: starch
    • sugar: sugar
  4. n: number of plots measured (unit: number / missing value: NA)
  5. mean: fraction of root dry weight, averaged per species and sampling date (g nonstructural carbohydrates/g dry roots) (unit: gramsPerGram / missing value: NA)
  6. se: standard error (unit: dimensionless / missing value: NA)

hf278-06: root respiration

  1. date: sampling date
  2. species: dominant tree species where the sample was collected
    • FRAM: Fraxinus americana
    • QURU: Quercus rubra
    • TSCA: Tsuga canadensis
  3. efflux.umol.co2.g.s: mass-specific root respiration (μmol CO2 g-1 s-1) (unit: micromolePerGramPerSecond / missing value: NA)