LTER Intersite Fine Litter Decomposition Experiment (LIDET), 1990 to 2002

ORIGINATOR: Mark E. Harmon
ABSTRACTOR: Mark E. Harmon
3 May 1992
4 Mar 2013
Inorganic nutrients, Organic matter, decay rates, decomposition, litterfall, inorganic nutrients, wood, carbon, nitrogen, phosphorus, organic matter, roots, fine roots, leaf litter
The primary objective of this study is to examine the control that substrate quality and climate have on patterns of long-term decomposition and nitrogen accumulation in above- and below-ground fine litter. Of particular interest will be to examine the degree these two factors control the formation of stable organic matter and nitrogen after extensive decay.
Experimental Design - TD023:

The major factors to be considered in this experiment will be site, species of and type of litter (leaves vs. roots vs. dowels) , and time. Twenty-one sites, representing a wide array of moisture and temperature conditions, will be used for litter incubations. Ten types of "standard" litters will be sent to each site. These include three types of fine roots (graminoid, hardwood, and conifer), six types of leaf litter (which range in lignin/nitrogen ratio from 5 to 75), and wooden dowels. Samples will be collected ten times; the time between samples will be one year for all sites except LaSelva and Luquillo which will collect samples every three months. There will be four replicates for each species, site and time.

In addition to the standard litters, each site will be represented by a "wildcard" litter which appears at one site for each sample collection. The purpose of the wildcard species is to verify the predictions from the standard species. There will be four replicates for each wildcard species, site and time.

Field Methods - TD023:

Litter Collection

Each site was responsible for collecting the litter used in the experiments. For most sites, the leaf litter was collected directly from senesecent plants or as freshly fallen litter. Green leaves were collected from the Jornada, San Diego, Luquillo, and LaSelva sites. All leaf litter except, Drypetes glauca which was oven dried at 40°C to prevent decay, was air dried prior to shipment to Oregon State University.

Fine roots (less than 2 mm diameter) were collected by two methods: tropical hardwood (Drypetes glauca) and pine (Pinus elliotii) fine roots were collected by excavating surface roots and washing. Graminoid roots were collected from material exposed along stream banks. Graminoid and pine roots were air dried, whereas the tropical hardwood roots were oven dried at 40°C to prevent decomposition.

In the case of the LaSelva site, the litter was sterilized after the bags were filled to kill all invertebrates, fungi, and virus prior to shipment. Sterilization was conducted at the Battelle National Laboratory by exposing the litter to 20 hours of gamma rays with 60Co as the source. The total exposure was 2 Mrad.

Bag Design

All bags were 20- by 20-cm and filled with 10 g leaves and 5-7 g of fine roots. Each bag was identified with a unique number embossed on an aluminum tag. The bag openings were sealed with six monel staples. The initial air dry weight, calculated oven dry weight, species, site, replicate number for each litterbag were recorded prior to placement in the field. Subsamples of litter material were taken to determine the air dry to oven dry conversion factor and the initial chemistry of the litter. Moisture content of the air dried litter ranged from 2-10% moisture content.

Three types of bags were used in this experiment. For the long-term leaf litter experiment the bags had a top mesh of 1 mm and a bottom of 55 micron mesh. The bags used for fine roots were entirely of 55 micron mesh. The bags used in the mesh size effects study had a top of 7 mm mesh and a bottom of 55 micron mesh.


The wooden dowels used in the experiment are made of ramin (Gonystlylus bancannus). This species is a tropical hardwood from southeast Asia. It is not resistant to decay and rated as perishable. The dowels are 13 mm in diameter and 61 cm in length. One half of the dowel is to be embedded vertically into the soil and the other half is to be exposed to aerial conditions. The air dry weight of each dowel was recorded, and a subsample of dowels was measured for diameter, density, air dry moisture content, nitrogen content, and carbon chemistry.

Sample Placement

Samples were placed in the field during fall of 1990 by each of the participating sites. Locations were near climatic stations and in areas protected from disturbances that could destroy the litter bags. The locations were also selected to be typical of areas that other intersite decomposition experiments might be conducted.

The exact method for placement varied from site to site, but the following standards were applied:

  1. Four separate locations were selected to avoid pseudo- replication problems.
  2. Each set of bags to be collected was connected by a cord; these sets of bags should be laid out in parallel lines in a random order.
  3. Leaf litterbags should be placed so that contact with the underlying litter layer is made. Fine root litterbags will be inserted into the upper mineral soil (humus layer for histosols). A vertical cut with a shovel, the bag inserted the correct depth (0-20 cm), and another cut should be used to press the soil against the bag (Figure 3).
  4. Dowels should be installed at the end of the string opposite the fine root bags. The dowels were placed so that 30 cm is exposed to the air and 30 cm is embedded in the soil.

Sample Processing

Once the litter or dowels are collected they should be oven dried in a paper bags at 55°C until the mass is stable. In the case of fine roots and dowels, a rinse with distilled water to remove adhering soil prior to drying is recommended. Any mosses, lichens, fine roots, or other plant parts that have grown into the bags or dowels should also be removed prior to harvesting. Samples will be pooled by species, site, and time for grinding and archiving. A subset of unpooled samples will also be saved to determine the internal variability of pooled samples. Chemical analyses will be performed using two methods. Each pooled sample from each species, site, and time will be analyzed for total nitrogen, lignin, and cellulose using near infrared reflectance spectoscopy (Wessman et al. 1988). Internal variability of samples will be estimated by running replicates of high and low lignin species. Twenty five percent of the pooled samples will also be sampled for Kjeldahl nitrogen, lignin, cellulose, water extractive, non- polar extractive, and ash content using wet chemical methods. Wet chemical methods will then be used to calibrate the near infrared reflectance spectoscopy methods.

Some entries under the attribute SPECIES in the various entities are not officially recognized species. They include: PICOB - Pinus contarta (brown leaves), PICOG - Pinus contorta (green leaves), TRFPR - Cover crop (KBS), TRFIN - Cover crop (KBS), COST - Corn stover, SOST - Soynean stover, WHST - Wheat stover, CONI - Coniferous leaf litter (KBS), DECI - Deciduous leaf litter (KBS), POPL - Poplar leaf litter (KBS), MIX - Mixed species, LICHE - Cladonia lichen
Garrison et al., 1976
Twenty-one sites across north and central america, representing a wide array of moisture and temperature conditions. Mainly LTER sites.
Ground condition

Wessman, C. A., J. D. Aber, D. L. Peterson, and J. M. Melillo. 1988. Foliar analysis using near infrared reflectance spectroscopy. Can. J. For. Res. 18:6-11

Ryan, M.G., Melillo, J.M., Ricca, A. (1990) A comparison of methods for determining proximate carbon fractions of forest litter. Canadian Journal of Forest Research, 20, 166-171.