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Harvard Forest Data Archive


Photosynthetic Light Response Curves in CRUI Land Use Project at Harvard Forest 1998

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  • Lead: Timothy Sipe, Richard Bowden, Charles McClaugherty
  • Investigators: Chelsea Halback, Brie Kessler, Melissa Kibler, Kyle Schwabenbauer, Matthew Wodkowski
  • Contact: Timothy Sipe
  • Start date: 1998
  • End date: 1998
  • Status: completed
  • Location: Prospect Hill Tract (Harvard Forest)
  • Latitude: +42.53 to +42.55
  • Longitude: -72.20 to -72.17
  • Elevation: 335 to 357 meter
  • Taxa: Acer rubrum (red maple), Aralia nudicaulis (wild sarsaparilla), Clintonia borealis (blue-bead lily), Medeola virginiana (indian cucumber-root), Quercus rubra (red oak)
  • Release date: 2009
  • Revisions:
  • EML file: knb-lter-hfr.139.10
  • DOI: digital object identifier
  • Related links:
  • Study type: short-term measurement
  • Research topic: historical and retrospective studies; large experiments and permanent plot studies; physiological ecology, population dynamics and species interactions
  • LTER core area: primary production, disturbance
  • Keywords: carbon dioxide, herbs, land use, light, photosynthesis, seedlings
  • Abstract:

    Ambient CO2 concentrations in terrestrial ecosystems vary substantially on several spatial and temporal scales as numerous soil, plant, and atmospheric processes respond to irradiance, temperature, moisture and wind. There is one widespread microhabitat in terrestrial ecosystems, the nearground zone, in which CO2 is naturally enhanced above average background levels. CO2 produced by soil respiration diffuses through the litter and boundary layers and dissipates fairly rapidly into the overlying bulk air. However, a marked vertical profile of nearground enriched CO2 (hereafter NEC) is usually present in the first 0-50 cm above ground. The degree of enrichment varies primarily with soil respiration rate and turbulent mixing, secondarily with photosynthesis by plants in the herbaceous stratum, and usually shows marked diel and seasonal variation. References to this CO2 "subsidy" and its effects on plants have occurred occasionally in the literature since 1939, but there have been few detailed studies of either the nearground profile or plant responses in the field, particularly for species that consistently occupy the nearground stratum.

    Considerable research over the last twenty years in both controlled and field environments has shown that co-occurring plant species may respond differently to artificially elevated CO2. But in contrast to light, temperature, water, and nutrients, plant community ecologists have generally not considered CO2 among the factors that regulate species’ distribution and abundance, except indirectly as it may affect water balance.

    We have documented differences in forest composition (woody and herbaceous), soil characteristics, microclimates, and nearground CO2 levels among six sites that were formerly plowed, pastured, or continuously forested woodlots in Prospect Hill. We selected three perennial herbaceous species (Aralia nudicaulis, wild sarsaparilla; Clintonia borealis, blue-bead lily; Medeola virginiana, Indian cucumber root) and two dominant tree species in the Harvard Forest system (Acer rubrum, red maple; Quercus rubra (northern red oak) and measured their photosynthetic light responses to ambient CO2 variation within the range commonly encountered in the field (350-450 ppm) to address five questions: (1) What is the overall effect of NEC on net carbon assimilation? (2) Do species differ overall (land use sites combined) in their responses to NEC? (3) Do the land use sites differ overall (species combined) in plant responses to NEC? (4) Are there site x CO2 or species x CO2 interactions in response to NEC?

    Light response curves were measured at three CO2 levels (350, 400, and 450 ppm inside the cuvette) on 3 randomly-selected, healthy replicates of each species in each of the three sites, generating a total of 135 curves. Gas-exchange measurements were made with a LI-6400 infrared gas analyzer (Li-Cor Inc., Lincoln, NE, USA) during ~7:30-12:30 a.m. solar time in late July and early August 1998. The analyzer was calibrated daily just prior to measurements. Air temperature in the cuvette was maintained at 23 deg C (mean morning air temperature in the sites), and relative humidity was maintained at either constant or slowly rising levels (typically less than 5% increase overall) during the 20-25 minutes required for each curve.

    Rectangular hyperbolic curves were fitted to the scatterplots and curve parameters (daytime respiration rate, Rday; apparent quantum efficiency, AQE; maximum assimilation rate, Amax; curve convexity; light compensation point, LCP; and light saturation point, Lsat) were estimated using Photosyn Assistant software v. 1.1 (Dundee Scientific, Dundee, Scotland, UK). Six of the curves produced questionable parameters in the quantum yield region and were excluded from further analyses, leaving a total sample size of 129.

  • Methods:

    Plot locations: Plow #2 Site: Prospect Hill Tract, Compartment # III, southern end. Pasture #1 Site: Prospect Hill Tract, Compartment # I, southeastern edge. Woodlot #2 Site: Prospect Hill Tract, Compartment # VII, central.

  • 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:

    Sipe T, Bowden R, McClaugherty C. 2009. Photosynthetic Light Response Curves in CRUI Land Use Project at Harvard Forest 1998. Harvard Forest Data Archive: HF139.

Detailed Metadata

hf139-01: light response curves

  1. species: six-letter genus-species abbreviations for the 5 taxa used in this study
  2. site: site
    • P2: Plow 2
    • S1: Pasture 1
    • W2: Woodlot 2
  3. co2: controlled ambient CO2 levels at which light response curves were measured (unit: dimensionless / missing value: NA)
  4. n: sample size (unit: number / missing value: NA)
  5. statistic: statistic
    • Mean: mean
    • std dev: standard deviation
    • std err: standard error
  6. rday.meas: daytime respiration rate at PPF = 0 actually measured during gas-exchange, in µmol C m-2 s-1. Included here since Rday values extrapolated from the curve fitting are sometimes questionable. (unit: micromolePerMeterSquaredPerSecond / missing value: NA)
  7. rday.curvefit: daytime respiration rate at PPF = 0 estimated from the curve fit (unit: micromolePerMeterSquaredPerSecond / missing value: NA)
  8. aqe: apparent quantum efficiency, slope of the initial linear portion of the light response curve (unit: dimensionless / missing value: NA)
  9. amax: maximum net assimilation rate estimated asymptotically from the fitted curve (unit: micromolePerMeterSquaredPerSecond / missing value: NA)
  10. convexity: convexity parameter for the fitted curve (unit: dimensionless / missing value: NA)
  11. lcp: light compensation point, estimated as the X-intercept by the fitted curve (unit: micromolePerMeterSquaredPerSecond / missing value: NA)
  12. lsat: light saturation point, calculated as the PPF value that corresponds to the intersection between the quantum yield slope and estimated Amax (unit: micromolePerMeterSquaredPerSecond / missing value: NA)