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Harvard Forest Data Archive

HF255

Root Exudation Simulation Experiment in a Red Oak Stand at Harvard Forest 2011

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Data

Overview

  • Lead: John Drake, Adrien Finzi
  • Investigators: Bridget Darby, Marc-Andre Giasson
  • Contact: Adrien Finzi
  • Start date: 2011
  • End date: 2011
  • Status: completed
  • Location: Prospect Hill Tract (Harvard Forest)
  • Latitude: +42.504361
  • Longitude: -72.199898
  • Elevation:
  • Taxa: Quercus rubra (red oak)
  • Release date: 2015
  • Revisions:
  • EML file: knb-lter-hfr.255.3
  • DOI: digital object identifier
  • Related links:
  • Study type: short-term measurement, modeling
  • Research topic: soil carbon and nitrogen dynamics
  • LTER core area: populations, organic matter
  • Keywords: biogeochemistry, carbon, microbes, modeling, nitrogen, oak, soil respiration
  • Abstract:

    Root exudation is thought to increase the activity of microbes and the exoenzymes they synthesize, leading to accelerated rates of carbon (C) mineralization and nutrient cycling in rhizosphere soils relative to bulk soils. The nitrogen (N) content of microbial biomass and exoenzymes may introduce a stoichiometric constraint on the ability of microbes to effectively utilize the root exudates, particularly if the exudates are rich in C but low in N. We combined a theoretical model of microbial activity with an exudation experiment to test the hypothesis that the ability of soil microbes to utilize root exudates for the synthesis of additional biomass and exoenzymes is constrained by N availability. The field experiment simulated exudation by automatically pumping solutions of chemicals often found in root exudates (“exudate mimics”) containing C alone or C in combination with N (C:N ratio of 10) through microlysimeter “root simulators” into intact forest soils in two 50-day experiments. The delivery of C-only exudate mimics increased microbial respiration but had no effect on microbial biomass or exoenzyme activities. By contrast, experimental delivery of exudate mimics containing both C and N significantly increased microbial respiration, microbial biomass, and the activity of exoenzymes that decompose low molecular weight components of soil organic matter (SOM, e.g., cellulose, amino sugars), while decreasing the activity of exoenzymes that degrade high molecular weight SOM (e.g., polyphenols, lignin). The modeling results were consistent with the experiments; simulated delivery of C-only exudates induced microbial N-limitation, which constrained the synthesis of microbial biomass and exoenzymes. Exuding N as well as C alleviated this stoichiometric constraint in the model, allowing for increased exoenzyme production, the priming of decomposition, and a net release of N from SOM (i.e., mineralization). The quantity of N released from SOM in the model simulations was, under most circumstances, in excess of the N in the exudate pulse, suggesting that the exudation of N-containing compounds can be a viable strategy for plant-N acquisition via a priming effect. The experimental and modeling results were consistent with our hypothesis that N-containing compounds in root exudates affect rhizosphere processes by providing substrates for the synthesis of N-rich microbial biomass and exoenzymes.

  • Methods:

    Please see Drake, J.E., Darby, B.A., Giasson, M.-A., Kramer, M.A, Phillips, R.P., Finzi, A.C., 2013. Stoichiometry constrains microbial response to root exudation—insights from a model and a field experiment in a temperate forest. Biogeosciences, 10, 821–838 for detailed methods.

    Soil respiration was also measured using an automated chambers system, but results were not included in the article mentioned above. Three automated chambers (surface area = 0.07m2) were used, coupled to the root exudation simulation treatments. During the two experiments, one chamber measured the water addition control, one measured the carbon-only addition treatment, and one measured the carbon+nitrogen addition treatment. Soil temperature was also measured inside each chamber using thermocouples.

    Each chamber was measured every 30 minutes, and soil respiration rates were computed according to the chamber area and volume and the rate of increase in the CO2 concentration in the chamber.

  • 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:

    Drake J, Finzi A. 2015. Root Exudation Simulation Experiment in a Red Oak Stand at Harvard Forest 2011. Harvard Forest Data Archive: HF255.

Detailed Metadata

hf255-01: soil respiration experiment 1

  1. datetime: date and time of measurement
  2. year: year of measurement
  3. doy: Julian day of measurement (unit: nominalDay / missing value: NA)
  4. hour: hour of measurement
  5. doy.dec: Julian day and decimal time of measurement (unit: nominalDay / missing value: NA)
  6. days.after.exp: number of days after the root exudation simulation started (negative values = pre-treatment) (unit: number / missing value: NA)
  7. chamber: soil respiration chamber identification number
  8. treatment: root exudation simulation treatment applied
    • Water: control
    • C: carbon addition
    • C+N: carbon and nitrogen addition
  9. rsoil: soil respiration rate (mg C/m2/hour) (unit: milligramPerMeterSquaredPerHour / missing value: NA)
  10. soilt: soil temperature inside the chamber (unit: celsius / missing value: NA)

hf255-02: soil respiration experiment 2

  1. datetime: date and time of measurement
  2. year: year of measurement
  3. doy: Julian day of measurement (unit: nominalDay / missing value: NA)
  4. hour: hour of measurement
  5. doy.dec: Julian day and decimal time of measurement (unit: nominalDay / missing value: NA)
  6. days.after.exp: number of days after the root exudation simulation started (negative values = pre-treatment) (unit: number / missing value: NA)
  7. chamber: soil respiration chamber identification number
  8. treatment: root exudation simulation treatment applied
    • Water: control
    • C: carbon addition
    • C+N: carbon and nitrogen addition
  9. rsoil: soil respiration rate (unit: milligramPerMeterSquaredPerHour / missing value: NA)
  10. soilt: soil temperature inside the chamber (unit: celsius / missing value: NA)