Decomposition and the release of nitrogen from litter is one of the most basic of all ecosystem processes. Despite the fact that the formation of "stable" soil organic matter and nitrogen are long-term processes, the majority of past studies on this process have been short-term. The primary objective of this study is therefore 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 is the degree these two factors control the formation of stable organic matter and nitrogen after extensive decay.
The major factors considered in this experiment are site, species of and type of litter (leaves, vs. roots vs dowels), and time. Twenty-eight sites (Table 1), representing a wide array of biomes (Table 2), moisture and temperature (Table 3) conditions, are used for litter incubations. Ten types of "standard" litters were sent to each site (Table 4). These included three types of fine roots (graminoid, hardwood, and conifer), six types of leaf litter (which ranged in lignin/nitrogen ratio from 5 to 75), and wooden dowels . Samples are to be collected ten times; the time between samples will be one year for all sites except tropical sites which will collect samples every three to six months. There are four replicates for each species, site and time.
In addition to the standard litters, each site is represented by a "wildcard" litter which appears at one randomly selected site for each sample collection. The purpose of the wildcard species is to verify the predictions from the standard species. There are 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. 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.
All bags were 20- by 20-cm and filled with 10 g leaves or 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%.
Three types of bags were used in this experiment (photo). 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 embedded vertically into the soil and the other half is 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.
Recovery of the initial dowels, particularly the below- ground portion, proved difficult. In 1994 a second group of wooden dowels was sent out to all LIDET sites. These dowels have a sleeve of 1 mm mesh on the lower 30.5 cm with an attached aluminum tag identical to the tag attached to the upper half of the dowel. A 20 cm section of orange plastic flagging was sewn into the top corner of the mesh sleeve to improve recovery.
Samples were placed in the field during fall of 1990, or 1991, 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 were laid out in parallel lines in a random order (photo).
3) Leaf litterbags were placed so that contact with the underlying litter layer is made (photo 3578 #28). Fine root litterbags were inserted 10-20 cm into the upper mineral soil or humus layer for histosols (photo).
4. Dowels were 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 (photo).
Once the litter or dowels are collected they are oven dried in paper bags at 55oC until the mass is stable. Any mosses, lichens, fine roots, or other plant parts that had grown into the bags or dowels were removed prior to harvesting. Samples were be pooled by species, site, and time for grinding and archiving. A set of unpooled samples has also be saved to determine the internal variability of pooled samples. Chemical analyses are performed using two methods. Each sample is analyzed for total nitrogen, ash, lignin, and cellulose using near infrared reflectance spectoscopy. Approximately 25% the pooled samples are sampled for ash, Kjeldahl nitrogen, lignin, cellulose, water extractive, non- polar extractive, and ash content using wet chemical. These samples are then used to calibrate the near infrared reflectance spectoscopy methods. Finally, the cation concentration of the pooled samples is determined using ICAP.
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Currie, W. S. 1995. Forest Floor Leachate Biogeochemistry and Decomposition Dynamics. Ph.D. Dissertation. Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH. 184 pp.
Currie, W. S. and J. D. Aber. 1997. Modeling leaching as a decomposition process in humid, montane forests. Ecology 78(6): 1844-1860.
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Harmon, M. E., K. J. Nadelhoffer, and J. Blair. in press. Measuring Decomposition, Nutrient Turnover, and Stores in Plant Litter. Pages XX-XX in Robertson, G. P., C. S. Beldsoe, D. C. Coleman, and P Sollins, editors. Standard Soil Methods for Long-term Ecological Research. Oxford University Press. Harmon, M. E. and K. Lajtha. in press. Analysis of Detritus and Organic Horizons for Mineral and Organic Constituents. Pages XX-XX in Robertson, G. P., C. S. Beldsoe, D. C. Coleman, and P Sollins, editors. Standard Soil Methods for Long-term Ecological Research. Oxford University Press.
Long-term Intersite Decomposition Experiment Team (LIDET). 1995. Meeting the challenge of long-term, broad-scale ecological experiments. Publication No. 19. US. LTER Network Office: Seattle, WA, USA. 23 p.
Moorhead, D. L., W. S. Currie, E. B. Rastetter, W. J. Parton, and M. E. Harmon. in review. Climate and litter quality controls on decomposition: an analysis of modeling approaches. Ecosystems
O'Lear, H. A., T. R. Seastedt, J. M. Briggs, J. M. Blair, and R. A. Ramundo. 1996. Fire and topographic effects on decomposition rates and N dynamics of buried wood in tallgrass prairie. Soil Biol. Biochem. 28:323-329.
Parton, W. J., D. S. Ojima, C. V. Cole, and D. S. Shimel. 1994. A general model for soil organic matter dynamics: sensitivity to litter chemistry, texture, and management. Soil Science Society of America Special Publication 39:147-167.
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Table 1. Twenty one sites are involved as of 10/90. These include the 17 LTER sites and 4 non-LTER sites. Seven additional sites were added in 1991 bringing the total to twenty-eight.
Table 2. The study includes all major terrestrial biomes in North America. Twenty-eight sites are involved. Individual site descriptions are stored in the TD2306 file.
Site Biome Andrews cool temperate conifer Arctic Lakes tussock tundra Barro Colorado Island moist tropical Bonanza Creek boreal conifer Blodgett State Forest temperate conifer Cedar Creek tall grass/ forest transition Short Grass Steppe shortgrass steppe Coweeta warm temperate hardwood Curley Valley cold desert Florida warm temperate conifer Guanica dry tropical forest Hubbard Brook cool temperate hardwood Harvard Forest cool temperate hardwood Jornada warm desert Juneau cool temperate conifer Kellogg agriculture Konza tallgrass prairie LaSelva wet tropical Luquillo wet tropical Loch Vale cold alpine conifer Monte Verde tropical cloud forest Niwot Ridge alpine tundra North Inlet coastal marine Northern Lakes cool temperate mixed Olympics cool temperate conifer Santa Margarita chaparral Sevilleta desert Virginia Coast coastal marine
Table 3. Climatic parameters for sites. Note these values should be checked against the most recent data for the sites.
Temp C Precip cm
Table 4. Species being tested in LIDET experiments. Those with a * are the "standard" species sent to each site each time.
ASPEN (Populus tremuloides) BEACH GRASS (Ammophila breviligulata) BEECH (Fagus grandifolia) BIG BLUE STEM (Schizachyrium gerardi) BLACK GRAMA (Bouteloua eriopoda) BLACK LOCUST (Robinea pseudoacacia) BLUE GRAMA (Bouteloua gracilis) CEANOTHUS (Ceanothus greggii) *CHESTNUT OAK (Quercus prinus) CREOSOTE BUSH (Larrea tridentata) DOUGLAS-FIR (Pseudotsuga menzesii) *DRYPETES (Drypetes glauca) EASTERN WHITE PINE (Pinus strobus) GYMNANTHES (Gymnanthes lucida) KOBRESIA (Kobresia myosuroides) LITTLE BLUE STEM (Schizachyrium scoparium) PACIFIC RHODODENDRON (Rhododendron macrophyllum) PACIFIC DOGWOOD (Cornus nuttalii) RAMIN (Gonystylus bancanus) *RED PINE (Pinus resinosa) *SLASH PINE (Pinus elliottii) SPARTINA (Spartina alternaifolia) SUBALPINE FIR (Abies lasiocarpa) *SUGAR MAPLE (Acer saccharum) VOCHYSIA (Vochysia ferragenea) WAX MYRTLE (Myrica cerifer) *WESTERN REDCEDAR (Thuja plicata) *WHEAT (Triticum aestivum) YELLOW BIRCH (Betula lutea) WHITE FIR (Abies concolor)