Canopy Chemistry Study

• Investigators: John Aber, Mary Martin
• Contact: Mary Martin
• Start date: 1992-01-01
• End date: 1992-12-31
• Location: Harvard Forest
• Latitude: +42.45 to +42.55
• Longitude: -72.23 to -72.16
• Elevation: 205 to 420 meters
• Taxa:
• Keywords: canopy chemistry, cellulose, lignin, nitrogen, remote sensing, spectroscopy
• Abstract:

  As part of NASA's Accelerated Canopy Chemistry Program (ACCP) analyses were performed for the determination of carbon constituents and nitrogen content in fresh forest foliage. Samples were analyzed using a series of extraction's that yielded different carbon constituents: non-polar, polar, cellulose and lignin. Nitrogen analyses were conducted using a standard combustion procedure. Approximately 1000 leaf samples were collected from 5 geographically distinct sites and were analyzed at the University of New Hampshire to ensure consistency in analysis. Results were used as a calibration set for Visible/NIR reflectance and the estimation of carbon and nitrogen concentrations at both the leaf and canopy level. The canopy level study uses high spectral resolution data from NASA's Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) to estimate canopy level nitrogen and lignin concentration for the Harvard Forest and other study areas.

  The current link to this data from the Harvard Forest LTER site is to an archive at the University of New Hampshire. Additional information on this study, including, leaf level spectra and remote sensing data are available from a NASA DAAC site (http://www-eosdis.ornl.gov/daacpages/accp.html). Additional foliar chemistry data is also available on a searchable on-line database at http://www.folchem.sr.unh.edu.

• Methods:

  Sample preparation

  Prior to analysis, samples were oven dried at 70 degrees C for 48 hours, ground to 20-mesh and homogenised.

  Proximate carbon fraction analysis

  Carbon constituent analyses were performed using a series of extraction's modified from those used by Ryan, et. al. Two grams of material were refluxed with 75 ml of dichloromethane for five hours to remove the non-polar component of the sample (fats, waxes, and other organic soluble materials) using a block digestor and condenser apparatus modified from a TAPPI procedure. Polar extractives such as phenols, simple sugars, starch and simple amino acids were removed by boiling a subsample (1.6 g) of tissue from the non-polar analysis for three hours in deionised water and then filtering. Sample size was increased from the recommended 0.5 g to 1.6 g to ensure sufficient post polar sample quantity for the acid digestion. Lignin and cellulose content were determined by a modified wood-products chemistry procedure. A 0.5 g subsample of post polar material was digested in 72% sulphuric acid for 1 hour in a 30 degree C water bath. This was then diluted with water until a 28:1 water to acid ratio was formed to carry out secondary hydrolysis while boiling for 4 hours. To wet the sample thoroughly we used 1.5 ml of acid for each 100 mg of sample, a 0.5 ml increase in acid over the quantity Effland recommended. At the end of this process the sample was filtered. Residual tissue was considered lignin and mass lost during digestion was considered cellulose. The percentages of the different constituents were determined gravimetrically. Oven-dried samples were temporarily stored in dessicators to prevent gaining moisture from the atmosphere before weighing.

  Calculations for carbon chemistry

  % non polar = (Pre non polar mass - post non polar mass)/ pre non polar mass; % polar = ((pre polar mass - post polar mass)/ pre polar mass) * (1-% non polar); % cellulose = ((pre digest mass - post digest mass)/ pre digest mass) * (1- % non polar - % polar); and % lignin = (post digest mass / pre digest mass) * (1- % non polar- % polar).

  Nitrogen analyses

  Nitrogen determination was performed using a Perkin-Elmer 2400 CHN Elemental Analyser. The CHN analyser combusts a sample to convert elements to gases (CO2, H2O, N2). The resulting data are weight percentage of carbon, hydrogen and nitrogen (CHN). In addition, a total Kjeldahl nitrogen (TKN) determination was performed on a subset of 100 samples. This method uses sulphuric acid and a digestion catalyst of potassium sulphate, cupric sulphate and selenium powder on ground leaf samples to generate a liquid sample for colorimetric analysis, and was included as a alternate method of nitrogen determination included for QA/QC as assessment. In addition, three replicate samples of each of the three standard materials were sent to Oregon State University for a similar Kjeldahl analysis. Finally, three National Bureau of Standards (NBS) 1.2% nitrogen pine foliage standards were included in each of four Kjeldhal runs.

• Related datasets: