DETRITAL SOURCES OF STABILIZED SOIL ORGANIC MATTER IN TEMPERATE FOREST

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: MCINTIRE-STENNIS
• Reporting Frequency: Annual
• Accession No.: 1007446
• Project Start Date: Oct 1, 2015
• Project End Date: Sep 30, 2018
• Program Code: [(N/A)]- (N/A)

Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853

Performing Department
Natural Resources

Non Technical Summary
In 2012, we initiated a field study to quantify sources of forest soil organic carbon using isotope-labeled plant detritus. Forest ecosystems play a major role in the global carbon cycle storing carbon in both live biomass and in soil organic matter. The effects of forest harvest on soil C sequestration are difficult to quantify because of the large, slowly changing pool size and high spatial variation; hence, the response of soil C to forest management activity is poorly constrained, and the process of soil organic formation is incompletely understood. This project utilizes isotope-labeled leaf litter, coarse woody debris, fine roots and woody roots, to investigate the process of soil organic matter formation. This research will enable more accurate predictions of the response of soil C pools to environmental changes and forest management activities, essential for evaluating this important sink in the global carbon budget. Such knowledge is essential for decision making in the realm of local, regional and global greenhouse gas management. The experiments are in place at two sites and results from the first-year collection (2013) for fine roots indicate that we will be able to quantify C sequestration in various soil aggregate pools in five different regional soil types with high accuracy and precision. Collection of the woody substrate samples are planned for years 3-6 (2015-2018).

Animal Health Component

(N/A)

Research Effort Categories

Basic

100%

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
123	0110	1070	100%

Knowledge Area
123 - Management and Sustainability of Forest Resources;

Subject Of Investigation
0110 - Soil;

Field Of Science
1070 - Ecology;

Keywords

soil carbon

woody biofuel

roots

aggregates

Goals / Objectives
The goal of the proposed research is to increase understanding of the process of stabilization of detrital C in forest soil. 1. To quantify the transformation of C in woody debris into underlying soil; the pools of soil carbon to which it contributes; and the effect of different classes of wood decay fungi (white vs. brown rot) in contributing to sequestration of woody debris carbon in soil. 2. To quantify stabilization of C from fine root detritus in different soil aggregate pools in comparison with leaf litter. 3. To quantify stabilization of C in woody root detritus in soil aggregate pools. 4. To inform policy makers of the implications of the research for long-term effects of intensified forest harvest on soil C sequestration.

Project Methods
We are utilizing plant tissues highly-enriched in 13C, including leaf litter, fine roots, woody roots and stem wood, to trace C into soil pools. The field study was initiated in 2012 and consists of three components, addressing the first three objectives. Study 1. The experimental design includes three treatments in terms of decay fungi: white-rot (inoculated), brown-rot (inoculated) and naturally occurring taxa (not inoculated). We plan to collect randomly-selected samples in 2015 (3 yr), 2016 (4 yr) and 2017 (5 yr). Enrichment of 13C will be quantified in each of six soil pools, including different soil aggregate components. Study 2. We inoculated highly 13C-enriched very fine (< 1mm) and fine (1-2 mm) in soil cores containing soil from five different regional soil horizons, including inceptisols, alfisols and spodosols. We have completed two collections from this study (2013 and 2014) and collections are planned for year 3 and 4. Again, enrichment of several soil fractions will be quantified. Study 3. We are tracing 13C from the woody roots of labeled trees (seven labeling chambers) into soil C pools. In 2012 we quantified 13C pools (one year after tree stems were harvested) to initiate this study. Soil pits will be excavated in year 3-6 (2015-2018), and 13C enrichment in various soil pools will be measured.

Progress 10/01/15 to 09/30/18

Outputs
Target Audience:Scientists, extension agents and foresters. Changes/Problems:The project was initiated with the plan to collect samples over a nine year period thereby allowing nearly complete stabilization of detrital carbon in soil organic matter. Funds have been fully expended to complete sample processing and analysis to date. Completion of project goals would require funds to allow processing of samples from the last three years of the planned project. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? The process of stabilization oforganic matter in forest soils is slow. Funding through the current period was sufficient to quantify the temporary stabilization of detrital organic matter derived from fine roots and woody detritus but at least three more years will be needed before the fate of this organic matter is conclusively established. Through the first three years we have demonstrated that fine root detritus has been recovered primarily in three soil fractions: particulate organic matter (POM), microaggregates andfine silt/clay. Levels in the last two fractions have gradually increased over the three years of collection whereas levels in the POM fraction showed a transient increase after two years followed by a decline in year 3. Although some differences in recovery have been observed across the five soil types, these patterns of change have generally prevailed. We anticipate that rates of change in recovery will slow by year 5; samples have been collected but processing is not complete. After three years of decay, woody detritus had lost about 55% of its original mass and carbon was recovered at high enrichment in all soil fractions, especially particulate fractions. Collections after five years indicated near complete decay of the wood in most samples. These samples are in storage (frozen) until funding can be obtained to permit processing and analysis. Our plan was to completefinal collections of woody detritus and soils in year 7 and 9 by which time we anticipate that woody detrital carbon would be nearly fully stabilized.

Publications

Progress 10/01/16 to 09/30/17

Outputs
Target Audience:Research colleagues Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?We trained an undergraduate student, Luz Jimenez, in methods of soil aggregate separation. How have the results been disseminated to communities of interest?We have communicated with colleagues about the initial results and interpretations of these experiments. What do you plan to do during the next reporting period to accomplish the goals?In the coming year under goal #1 we will be analyzing isotope enrichment of hundreds of decaying wood samples and surface soil samples to quantify C stabilization in soil organic matter. Under goal #2, we will be collecting the fourth set of fine root samples to quantify the stabilization of fine root carbon in various soil organic matter pools. Under goal #3 we will be analyzing isotope enrichment in residual woody roots and soil organic matter to quantify the stabilization of woody root carbon in various soil organic matter pools. Under goal #4, we plan to develop a published report on the fate of fine root carbon under goal #2. We also plan to report our observations at a national meeting, probably American Geophysical Union.

Impacts
What was accomplished under these goals? During the past year under goal #1, we collected a second set of woody debris samples from the field sites. We quantified dry weight loss from decaying wood. Subsamples are preserved in preparation for isotope analysis. Under goal #2 we collected and processed a second set of fine root decay chambers from the field sites and measured the stabilization of isotopically labeled fine root organic matter in several aggregate pools in the soil. Samples have been prepared for isotopic analysis which is currently underway. Under goal #3 we collected a set of woody root samples. Samples have been processed and prepared for isotope analysis. Under goal #4 no accomplishments are reported at this intermediate stage in the research project.

Publications

Progress 10/01/15 to 09/30/16

Outputs
Target Audience:Professional colleagues studying the problem of sources of stabilized soil carbon in forests. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?We trained an undergraduate student - Steve Breitenstein - who completed a Senior Honors Thesis on stabilization of fine root carbon. He learned about the scientific process, measurement of soils and aggregates, isotopic tracer approaches and statistical methods. How have the results been disseminated to communities of interest?The results have been disseminated to scientific colleagues through informal communications. What do you plan to do during the next reporting period to accomplish the goals?In the coming year under goal #1 we will be collecting the second set of woody debris samples to quantify the stabilization of wood carbon in various soil organic matter pools. Under goal #2, we will be collecting the third set of fine root samples to quantify the stabilization of fine root carbon in various soil organic matter pools. Under goal #3 we will be collecting the first set of woody root samples to quantify the stabilization of woody root carbon in various soil organic matter pools. Under goal #4, we plan to develop a published report on the fate of fine root carbon under goal #2. We also plan to report our observations at a national meeting.

Impacts
What was accomplished under these goals? During the past year under goal #1, we collected a set of woody debris samples from the field sites. We have identified several fungi that are decomposing the wood and we measured isotope enrichment in the fruiting bodies of those fungi. The wood samples are preserved in preparation for isotope analysis. Under goal #2 we collected and processed a set of fine root decay chambers from the field sites and measured the stabilization of isotopically labeled fine root organic matter in several aggregate pools in the soil. After three years about 15% of the original fine root carbon has been stabilized, mostly in the particulate organic carbon pool in the soil. Under goal #3 we have delayed the collection of woody root samples because field observation suggested that decay was minimal after two years of incubation. The next set of samples will be collected in year 4 of decay (2017). Under goal #4 no accomplishments are reported at this intermediate stage in the research project.

Publications