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Harvard Forest Data Archive
20-Year Root Mass in Chronic Nitrogen Amendment Experiment at Harvard Forest 2008Related Publications
- Lead: Richard Bowden, Serita Frey
- Investigators: Knute Nadelhoffer
- Contact: Richard Bowden
- Start date: 2008
- End date: 2008
- Status: completed
- Location: Prospect Hill Tract (Harvard Forest)
- Latitude: +42.5425
- Longitude: -72.1813
- Elevation: 406 meter
- Release date: 2011
- EML file: knb-lter-hfr.166.8
- DOI: digital object identifier
- Related links:
- Study type: short-term measurement
- Research topic: large experiments and permanent plot studies; soil carbon and nitrogen dynamics
- LTER core area: organic matter, disturbance
- Keywords: biomass, nitrogen, roots
Forests typically respond to nitrogen additions with increased productivity, hence a long-held paradigm was that chronic additions of anthropogenically-derived atmospheric deposition would have positive ecosystem effects. However, twenty years of work at the Harvard Forest Chronic N Deposition plots, and in other forest ecosystems as well, has shown that that this simplistic view is incomplete. For example, enhanced ammonium uptake increases soil acidity, leading to mobilization of aluminum, and loss of nutrient cations (e.g. Mg2+, Ca2+, and K+ ) all of which influence root mass, turnover, and activity.
To address long-term impacts of N additions on forest root mass, we removed O-horizon (forest floor) samples from the Chronic N hardwood and red pine stands to quantify the total mass of roots.
We found that long term N additions had contrasting results in the two forests. In the hardwood plots, total root mass (less than 2mm) increased from 0.167 + 0.026 (S.E.) kg m-2 in the control plot to 0.434 + 0.170 kg m-2 in the high N plots. In contrast, in the red pine stand, roots declined from 0.074 + 0.011 (S.E.) kg m-2 in the control plot to 0.031 + 0.016 kg m-2 in the high N plots. These data are in agreement with data for aboveground productivity at the Chronic N plots, which show stimulated growth in the hardwoods and severe growth declines and enhanced mortality in the pine stand.
In 2008, we collected three to six 20x20cm O horizon samples each of each of the Control, Low N, and High N plots, in both the hardwood and red pine stands. Samples were frozen immediately after collection, and returned to Allegheny College for analysis. Samples were thawed just prior to collection, and those roots systems that were most intact were removed initially to maintain as complete a root system as the sample size would allow. These roots were kept for a related study on root order and C and N uptake activity and refrozen; these roots were later surface dried briefly to remove surface water, and weighed so that, after obtaining air-dry:oven-dry conversions, the mass of this root material could be added into the total mass for each sample. All remaining roots were extracted manually from each sample, washed, and divided into the following diameter classes: greater than 2 mm, between 1 and 2 mm, and less than 1mm. Roots were kept moist during the sorting process, and then refrozen when sorting was complete. Roots later were subsequently dried at 105C for 48 hours, mass was determined, and samples were ground in a Wiley Mill to pass through a no. 20 mesh sieve for later C and N analysis.
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.
Bowden R, Frey S. 2011. 20-Year Root Mass in Chronic Nitrogen Amendment Experiment at Harvard Forest 2008. Harvard Forest Data Archive: HF166.
hf166-01: root mass
- stand: stand
- Hardwood: Chronic N Hardwood stand
- Pine: Chronic N Red Pine stand
- treatment: annual N addition
- Control: 0 kg N/ha/y
- 50: 50 kg N/ha/y
- 150: 150 kg N/ha/y
- replicate: forest floor sample in each stand & treatment (1-6)
- sample.id: unique name of subplot from which each forest floor sample was obtained
- percent.0: percentage of total roots less than or equal to 1mm diameter (unit: dimensionless / missing value: NA)
- percent.1: percentage of total roots greater than 1 mm and less than 2mm diameter (unit: dimensionless / missing value: NA)
- percent.2: percentage of total roots greater than 2mm diameter (unit: dimensionless / missing value: NA)
- mass.0: oven dry biomass of roots less than or equal to 1mm diameter (unit: gram / missing value: NA)
- mass.1: oven dry biomass of roots greater than 1 mm and less than 2mm diameter (unit: gram / missing value: NA)
- mass.2: oven dry biomass of roots greater than 2mm diameter (unit: gram / missing value: NA)