Report from the LTER 2000 All Scientists Meeting

From the

Workshop Entitled “Long-term Decomposition studies in the LTER Network”

Held at Snowbird, Utah; on August 3, 2000

 

Compiled by Mark Harmon

 

The objectives of this workshop were to review the status of the LIDET and CIDET experiments, present preliminary results, and then to discuss future plans regarding analysis and future experiments. 

 

There were approximately 35 participants in the workshop, only 11 of whom represented sites participating in the experiment. 

 

After a review of the status of publications to date (see attached list), the sites collections, data management, and chemical analysis there were two presentations on preliminary analysis. 

 

The majority of sites (18) will complete the field portion of the study this year.  Another 4 sites will reach completion in 2001.  Two sites were unable to carry out the study past the second year, two sites had litterbags partially destroyed by fire, and 3-4 sites have been unable to collect surface litterbags due to degradation of the bag material after the fifth or sixth year.  Despite losing samples and sites the study has created an unprecedented set of data on long-term decomposition dynamics.  Litterbag Central has completed NIR scans on the complete set of samples from tropical sites, and up to the 6-8th collection for the other sites.  The scanning of all sites will be completed early winter 2000 with the exception of several sites that started their fieldwork a year after the main set of sites.  NIR based predictions of ash, N, and lignin are completed for the first 5 collections on all sites except the tropical sites which, with the exception of Monte Verde, have been completed for all samples.  Litterbag Central is also about to release data on the chemistry of fresh litter from sites.  This will allow users to search our database for species, to connect to sites that give other information on the species, and to see the litter as well.  The species include not only the ones used in LIDET but also ones collected from the sites after the experiment was started.  Hopefully this will become a widely used resource for modeling and other analyses. 

 

Henry Gholz reviewed an analysis that he led (with help from Steve Smitherman, Dave Wedin, Bill Parton, and Mark Harmon) that is about to be published in Global Change Biology.  Very strong relationships between climatic variables and decomposition rates for the first 5 years were found for Drypetes and Pinus litter.  Belowground decomposition was faster than aboveground decomposition with the exception of sites with high water tables.  At the latter sites decomposition below ground was very slow.

 

Mark Harmon reviewed the material he would present at ESA.  The basic conclusion is that the amount of stable material formed by decomposing litter was a function of both the species being decomposed and the environment at the site.  Two species (Pinus and Drypetes) were examined at two sites (Luquillo and Andrews).  As expected both litters formed less stable material at Luquillo than Andrews.  However, considerable stable material appears to have been formed (or have remained?) from Pinus needles at Luquillo.  Based on the range observed at these two sites, stable matter is equivalent to between 5 and 30% of the mass of the initial litter.  Guestimates of the slope that the stable matter is declining indicates that this stable matter has a decomposition rate-constant of 0.08 per year at Andrews and between 0.18 and 1.4 per year at Luquillo.  The source of this stable matter is not known at this point although it does seem to correlate with the fraction of initial lignin at the Luquillo site.  Additional analysis of the other sites as well as the chemistry of the stable matter should yield insights into the degree stable matter represents residual recalcitrant material or the degree it represents newly formed recalcitrant material.  Data from all papers published to date are available on the LIDET website (http://www.fsl.orst.edu/lter/datafr.htm click on data available now, and carbon dynamics, the dataset name is td23).  A bibliography will also soon be available from a related website that describes the study and sites (http://www.fsl.orst.edu/lter/research/intrsifr.htm click on LIDET). 

 

Tony Trofymow reviewed the status of the CIDET study.  This includes a total of 21 forested sites with a total of 11 types of litter.  The study has collected samples at an annual interval for 6 years, with a total of 10 sample collections.  Due to the slow decomposition observed at some sites, the study may be extended to 12 years by switching to biannual collections from here on out.  Papers describing the initial litter chemistry including 13C-NMR and results from the first 3 years are published, and Tony presented data from the first 6 years.  There is little evidence of formation of stable organic matter at this point from the CIDET study.  However, the influence of both substrate quality and climate are clear from the first six years of data.  Temperature was the main controlling climatic variable although growing degree-days was also important.  Klason lignin to N ratio was the best substrate quality indicator for long-term decomposition.  More details about CIDET can be found at www.pfc.forestry.ca/climate/cidet. 

 

These presentations were followed by a discussion of strategies to analyze the data, new types of chemical analysis, and new field experiments. 

 

Data Analysis.  It is clear that LIDET and CIDET are producing an unprecedented amount of information on the long-term decomposition dynamics of litter.  We are approaching the end of the field phase of the project and entering the analysis phase.  It is therefore quite possible that the players involved in the study are about to change.  Mark Harmon agreed to poll the original members of LIDET and determine their interest in participating in the analysis phase of the project.  Mark Harmon, Whendy Silver, and Bi;; Parton will lead the development of a NCEAS proposal to bring scientists together to begin the analysis of this goldmine of data.  A planning workshop sponsored by the Network Office will initiate these activities.  The participants agreed that it would be good to include LIDET and CIDET related data in this activity and pull in other studies to the degree they add insights.  An example of the latter would be the Microbial and Decomposition (MAD), an IBP era dataset.  Another possibility would be to include participants from Eastern Europe, as they have also conducted long-term litter decomposition experiments We will probably have two to three workshops at NCEAS, first identifying the papers to be written (although the 1996 Sevilletta workshop did a very good job of that), performing the analysis and writing, and finishing with a workshop that analyses future needs, experiments, chemical analysis, etc.  In addition to NCEAS, the participants were encouraged by Eldor Paul to consider submitting a proposal to DOE’s Global Change program.  This might be a good place to fund a global level extrapolation of the results. 

 

Chemical Analysis.  Litterbag Central has received funding from NSF to conduct some forms of chemical analysis on the samples.  This includes determination of ash, N, lignin, and cations.  The former 3 items are subsampled with values for all samples predicted from NIR.  These parameters are useful, but will not be sufficient for determining the chemical origin of the stable fraction.  One question raised was whether there were chemical similarities between the species and sites.  Analysis using 13CNMR, stable isotopes, quantitative pyrolysis, and methods for chitin were suggested.  There are many possibilities, but there are two limitations: 1) lack of instrumentation and 2) lack of samples.  In the short time there is little that can be done about the first limitation.  Perhaps NEON will increase these capabilities in the US.  The second will have to determined by careful release of the samples for essential analysis.  Tim Fahey agreed to send Mark Harmon the guidelines used by Hubbard Brook for requests of samples.  This may help us solve the second limit. 

 

Future Questions/Experiments.  The majority of the participant’s energies were focused on this topic.  One major topic of discussion was of critical areas to improve our understanding of long-term litter decomposition and the fate of the so-called stable matter.  These included:

 

1-more species.  LIDET and CIDET have included about 40 species, that leaves about 50,000 or more to go!  A combination of the standard library of litter chemistry and more species examined in the field will be helpful.  The Asian litter transplant experiment that is planned should add 10 or so species. 

 

2-more sites.  More sites particularly in warmer environments would greatly complement the LIDET and CIDET studies.  These studies need to be designed to determine the amount of stable material, a phase rarely examined in the tropics and subtropics. 

 

3-more parts.  Additional information on wood and root decomposition would help broaden our view of the formation of stable organic matter.  Mark Harmon is currently running a 15 site wood decomposition experiment.  Additional sites would be useful.  Root decomposition studies are far less common that leaf litter experiments.  The latter may need methodological developments as roots do not die out of contact with the soil as they are in litterbags. 

 

4-exchange of stable organic matter.  The amount of stable matter observed in LIDET and CIDET could be due to differential rates of formation or differential rates of decomposition of this material.  There are indications that the decomposition of stable material differs between sites and species, but the controls on initial amounts are very poor.  Therefore it might make more sense to collect stable matter formed by different processes or at different sites and to try a reciprocal transplant experiment.  The main question this would address is whether the process that formed the stable organic matter is more important than the environment in determining the rate of decomposition of this material. 

 

5-fate of lignolytic compounds in soil.  During the course of decomposition soluble material is leached from the litter and added to the soil.  What is the fate of this material?  Jean Lodge suggested this might be examined by rolling logs that were subjected to either white or brown rot and then examining the decline in these compounds in the underlying soil. 

 

6-chemical changes associated with Phase 1 of decomposition.  Ecologists have not paid a great deal of attention to the earliest, rapid loss phase of decomposition.  Both LIDET and CIDET were conducted on a coarse time interval; a detailed examination of the earliest phase of decomposition might improve our overall understanding of decomposition dynamics.  What are the chemical changes associated with this phase and what do they imply about the inputs to underlying layers.  This information is essential for whole ecosystem models that need to track these exchanges of material. 

 

7- improved methods.  Two areas were mentioned.  First, as suggested by Tim Fahey the effect of placing roots into a litterbag need to be tested.  It is a very simple method, but it may decrease the decomposition rate by excluding organisms and by reducing contact with the soil.  The second area was to try to correct for infiltration of litterbags by roots or other material.  This evidently has been a significant problem at Hubbard Brook.  Stable isotope measurements might be useful in this regard as suggested by Dave Wedin.

 

8-invertebrates effects.  LIDET and CIDET have primarily examined the issues of climate and litter quality.  The influences of invertebrates and other organisms are not addressed in a significant manner.  The IBOY experiments currently being implemented by Diana Wall may help out to some degree on this front. 

 

9-microenvironment effects.  In LIDET and CIDET we are using general climatic stations as a surrogate for local climatic conditions.  CIDET is actually addressing this issue for one year, by placing temperature sensors inside litterbags.  Another problem is that many models use soil moisture as a surrogate for litter moisture.  This can work in some situations, but not in others.  If climate changes it might change the relationship between specific sites and climatic stations or the soil changes. 

 

10-temporal effects.  This would include the season that decomposition starts and the variation from year to year. 

 

11-physical examination of litter layers.  Additional insights might be gained by examining the development of stable material visually.  The suggestion from Hen-Biau King would be to thin section litter layers after impregnating them with epoxies or other stabilizing materials.  If the various ages of material could be identified then one could infer the rate at which the transformations are occurring.  Kate Lajtha pointed out that Rich Qualls was placing mesh on the litter surface each year to determine chemical changes?