Harvard Forest

Data Archive

HF458

Root Traits and Exudation in the Soil Warming Plus Nitrogen Addition Experiment at Harvard Forest 2023

Related Publications

Data

• hf458-01: traits (preview)

Overview

• Lead: Thomas Muratore, Nikhil Chari, Serita Frey, Shersingh Joseph Tumber-Dávila
• Investigators: Isa Gooijer, Anisa Robinson, S. Grady Welsh, Benton Taylor
• Contact: Information Manager
• Start date: 2023
• End date: 2023
• Status: complete
• Location: Prospect Hill Tract (Harvard Forest)
• Latitude: +42.8333 degrees
• Longitude: -72.3000 degrees
• Elevation: 365 meter
• Datum: WGS84
• Taxa: Acer rubrum (red maple), Quercus rubra (red oak)
• Release date: 2026
• Language: English
• EML file: knb-lter-hfr.458.1
• DOI: digital object identifier
• EDI: data package
• DataONE: data package
• Related links:
• Study type: long-term measurement, short-term measurement
• Research topic: forest-atmosphere exchange; large experiments and permanent plot studies; physiological ecology, population dynamics and species interactions; soil carbon and nitrogen dynamics
• LTER core area: primary production, organic matter movement, mineral cycling
• Keywords: fine roots, maple, oak, rhizosphere, roots, soil carbon, soil nitrogen, soil warming
• Abstract:

  Fine-root traits and root exudation regulate plant–microbe interactions, nutrient cycling, and belowground carbon inputs, but it remains unclear whether root exudation is coordinated with broader root economic traits or responds independently to changing soil conditions. This dataset contains fine-root morphology, chemistry, and exudation measurements from Acer rubrum and Quercus rubra roots collected during the 2023 growing season at the Harvard Forest Soil Warming × Nitrogen Addition Study in Petersham, Massachusetts, USA.

  The experiment is a long-term factorial global change manipulation with four treatments: control, nitrogen addition, soil warming, and combined soil warming plus nitrogen addition. Soil warming has been maintained at 5°C above ambient since 2006, and nitrogen addition treatments receive 50 kg N ha-1 yr-1 as aqueous NH4NO3 during the growing season. The forest canopy is dominated by ectomycorrhizal Quercus rubra and arbuscular mycorrhizal Acer rubrum.

  This dataset includes measurements of specific root exudation rate, root mass, root tip number, root length, root diameter, root volume, root surface area, root carbon concentration, root nitrogen concentration, and root C ratio. Root exudates were collected in situ from intact fine-root systems using a modified cuvette incubation method, and root morphological traits were measured from scanned root images. These data were collected to evaluate how soil warming, nitrogen addition, species identity, and their interaction influence root exudation and root trait coordination.

• Methods:

  Study site and experimental design

  Data were collected at the Soil Warming × Nitrogen Addition Study at the Harvard Forest Long-Term Ecological Research site in Petersham, Massachusetts, USA. The experiment consists of twenty-four 3 × 3 m plots arranged in a fully factorial design with four treatments: control, nitrogen addition, soil warming, and combined soil warming plus nitrogen addition. Each treatment is replicated six times, except the warming-only treatment, which has five replicates due to a heating system failure in one plot in 2010.

  Soil warming has been maintained at 5°C above ambient since 2006 using electric heating cables installed at 10 cm depth and spaced 20 cm apart. Nitrogen addition treatments began in 2006 and receive 50 kg N ha-1 yr-1 as aqueous NH4NO3, applied monthly during the growing season from May through October. The forest canopy is dominated by Quercus rubra and Acer rubrum.

  Root exudation collection

  Root exudates were sampled five times during the 2023 growing season, with sampling events spaced approximately two weeks apart from May through August. One fine-root segment approximately 10–15 cm long was excavated from Acer rubrum and Quercus rubra in each plot when available. Roots were kept attached to the parent plant during exudate collection. Roots were gently rinsed with deionized water and cleaned with forceps to remove adhering soil particles.

  Each cleaned root segment was inserted into a 40 mL glass syringe packed with acid-washed glass beads and saturated with sterile, carbon-free nutrient solution. Syringes were sealed around the root entry point and insulated with leaf litter to approximate field soil conditions. Roots were first incubated for 48 h as an acclimation period. After the acclimation period, the solution was removed, cuvettes were rinsed twice with fresh nutrient solution, and the cuvettes were refilled for a final 24 h exudate collection period. At the end of the 24 h incubation, roots were severed immediately before exudate collection. Exudate solutions were collected and stored at -80°C until analysis. Root-free blank cuvettes were included during each sampling event and processed identically to account for background carbon contamination.

  Total organic carbon analysis and exudation rate calculation

  Total organic carbon in exudate solutions was measured as non-purgeable organic carbon using a Shimadzu TOC-L analyzer with an ASI-V autosampler. Total organic carbon concentrations were multiplied by total incubation volume and corrected using average blank values from root-free cuvettes. Specific root exudation rates were calculated by normalizing carbon accumulation during the 24 h incubation by root surface area and incubation duration. Exudation rates are reported as µg C cm-2 root h-1.

  Root morphology and chemistry

  Roots used for exudate collection were scanned in grayscale using a PlusTek OpticSlim A3 flatbed scanner at 400 dpi. Images were processed using RhizoVision Explorer under the “Broken roots” setting. The software was used to quantify total root length, root volume, average diameter, root tip number, and branching intensity. Image processing parameters were standardized across all samples. Root surface area from image analysis was used to calculate area-standardized exudation rates.

  After scanning, roots were dried at 60°C and weighed to determine dry mass. Morphological traits were calculated from image analysis and biomass data. Root carbon and nitrogen concentrations were measured on dried, homogenized root material using a Costech ECS 410 elemental analyzer at the Environmental Measurements Laboratory at Dartmouth College. Root C ratio was calculated from measured carbon and nitrogen concentrations.

  Data quality control

  Blank-corrected exudation values were used for calculation of specific root exudation rates. One exudation outlier exceeding five standard deviations from the mean was excluded prior to analysis.

• Organization: Harvard Forest. 324 North Main Street, Petersham, MA 01366, USA. Phone (978) 724-3302. Fax (978) 724-3595.

• Project: The Harvard Forest Long-Term Ecological Research (LTER) program examines ecological dynamics in the New England region resulting from natural disturbances, environmental change, and human impacts. (ROR).

• Funding: National Science Foundation LTER grants: DEB-8811764, DEB-9411975, DEB-0080592, DEB-0620443, DEB-1237491, DEB-1832210, DEB-1832110, DEB-1456610, DBI-1950364.

• Use: This dataset is released to the public under Creative Commons CC0 1.0 (No Rights Reserved). Please keep the dataset creators informed of any plans to use the dataset. Consultation with the original investigators is strongly encouraged. Publications and data products that make use of the dataset should include proper acknowledgement.

• License: Creative Commons Zero v1.0 Universal (CC0-1.0)

• Citation: Muratore T, Chari N, Frey S, Tumber-Dávila S. 2026. Root Traits and Exudation in the Soil Warming Plus Nitrogen Addition Experiment at Harvard Forest 2023. Harvard Forest Data Archive: HF458 (v.1). Environmental Data Initiative: https://doi.org/10.6073/pasta/7545c7fa931242f8cdf189c7e80a5f20.

Detailed Metadata

hf458-01: traits

1. Week: sampling week or sampling event during the 2023 growing season
2. Plot: experimental plot identifier
3. Trt: experimental treatment category
   • C: control
   • N: nitrogen addition
   • H: soil warming
   • HN: soil warming plus nitrogen addition
4. heat: soil warming treatment indicator
   • 0: ambient/control temperature
   • 1: heated 5 degrees C above ambient
5. nit: nitrogen addition treatment indicator
   • 0: no nitrogen addition
   • 1: nitrogen addition
6. Species: tree species identity for sampled root
   • acru: Acer rubrum
   • quru: Quercus rubra
7. roi: region of interest or root image/sample identifier used during image analysis
8. mass: dry mass of scanned root sample (unit: gram / missing value: NA)
9. c_rate: specific root exudation rate normalized by root surface area and incubation time (unit: microgramPerCentimeterSquaredPerHour / missing value: NA)
10. tips: number of root tips measured from scanned root image (unit: dimensionless / missing value: NA)
11. length: total root length measured from scanned root image (unit: centimeter / missing value: NA)
12. diam.u: unweighted mean root diameter or diameter output from image analysis (unit: millimeter / missing value: NA)
13. diam.m: mean or mass/length-weighted root diameter from image analysis (unit: millimeter / missing value: NA)
14. vol: root volume measured from scanned root image (unit: centimeterCubed / missing value: NA)
15. surfacearea: root surface area measured from scanned root image and used to calculate specific exudation rate (unit: centimeterSquared / missing value: NA)
16. c: root carbon concentration measured by elemental analysis (unit: dimensionless / missing value: NA)
17. n: root nitrogen concentration measured by elemental analysis (unit: dimensionless / missing value: NA)
18. cn: root carbon-to-nitrogen ratio calculated from root carbon and nitrogen concentrations (unit: dimensionless / missing value: NA)