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