Source: UTAH STATE UNIVERSITY submitted to NRP
BIOTIC VS ABIOTIC INFLUENCES ON THE STABILITY OF SOIL ORGANIC CARBON IN ASPEN-CONIFER FOREST EXOSYSTEMS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
MCINTIRE-STENNIS
Reporting Frequency
Annual
Accession No.
0228764
Grant No.
(N/A)
Cumulative Award Amt.
(N/A)
Proposal No.
(N/A)
Multistate No.
(N/A)
Project Start Date
Jul 1, 2011
Project End Date
Jun 30, 2016
Grant Year
(N/A)
Program Code
[(N/A)]- (N/A)
Recipient Organization
UTAH STATE UNIVERSITY
(N/A)
LOGAN,UT 84322
Performing Department
Wildland Resources
Non Technical Summary
Soil Organic Carbon (SOC) has an impact on the carbon that is released into the atmospohere and issues related to SOC at the margins of different forest types have important implications for the ability to soils to hold organic carbon. This study intend to answer this question for the aspen conifer interface.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1020199107055%
1230612107015%
1230622107015%
1210799107015%
Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships; 123 - Management and Sustainability of Forest Resources; 121 - Management of Range Resources;

Subject Of Investigation
0612 - Conifer forests of the West; 0622 - Broadleaf forests of the West; 0799 - Rangelands and grasslands, general; 0199 - Soil and land, general;

Field Of Science
1070 - Ecology;
Goals / Objectives
The goal of this combined field-laboratory study is to investigate the pathways of soil organic carbon (SOC) stabilization in forest soils and specifically the role of abiotic (soils, temperature, moisture, hydrology) and biotic (vegetation, microbial population) in creating differences in SOC persistence among forest types or among forest conditions. We will use the transition between aspen and conifer forests in Utah as our model system since we know these forest types exhibit contrasting SOC distribution and stability patterns. Specifically we will study the mechanisms behind the greater persistence of SOC in aspen forest soils as well as ho and how fast that SOC becomes destabilized as aspen forests are increasingly envaded by conifers.Our project will be based on soil samples (0-15cm) taken at various sites in Utah that have marked aspen-conifer transition zones. We will subject the samples to various physical (simplified size-density) and biological fractionation (incubation, water extraction) schemes in the lab to provide insight into the nature of the differences in SOC stability under pure and mixed aspen and conifer forests. This will followed by C analysis of solid and liquid phases to determine whether and to what extent belowground C chemistry are linked to aboveground forest cover characteristics. Through a series of laboratory experiments we will then test the relative importance of C inputs derived from decaying roots (belowground) or from leaf litter leachates (aboveground) to overall storage and relative stability of SOC in aspen vs conifer forest soils. We will also test through a variety of laboratory assays, whether the differences in SOC storage and stability is in any way linked to or caused by fundamental differences in composition and/or activity of soil microbial populations in aspen vs conifer soils. In the second phase of the project we will try to unravel what happens to the SOC as conifers invade aspen forests. By sampling plots in various degrees of aspen-conifer mixtures, we will assess whether there is a gradual loss of aspen-derived (stable) SOC with increased conifer occupancy or whether changes occur stepwise and at what critical threshold(s) of conifer dominance. This requires that we are able to distinguish what part of the SOC is from aspen vs conifer origin. In collaboration with colleagues in Germany will test the utility of Infrared Spectroscopic techniques - a non-destructive technique used to characterize the composition of a variety of organic substrates (e.g., animal forage, food) - to determine relative species contributions to SOC embedded within a mineral soil matrix.
Project Methods
Changes in environmental conditions (climate) and substrate availability (type and amount of detritus input) associated with vegetation cover shifts will likely be translated and detectable in microbial population shifts (Obj. 1.c). Specifically we will measure whether SOC stability is associated with low microbial abundance or with lack of specific organism groups able to process particular SOC compounds. Information gleaned from these experiments, collectively, will allow us to quantify how much SOC is stabilized along a gradient on forest cover ranging from pure aspen to pure conifer, and what pathways are most important in SOC stabilization. The FTIR assays, in particular, will provide important new insights into the relationship between forest cover, chemical composition of SOC sources, and SOC stabilization. (2) Destabilization and loss of SOC from the mineral soil during succession. In order to understand what happens to the aspen-derived "stable" SOC following conifer encroachment (Obj 2.b), we must be able distinguish an aspen signature in the SOC and possibly in the different fractions where SOC is more or less protected. Through collaboration with colleagues in Germany (University of Freiburg) we have begun to explore the utility of Near Infrared Reflectance Spectroscopy (NIRS) to determine relative species contributions in SOC embedded within a mineral soil matrix. However, to our knowledge this novel approach has not been applied to detecting the vegetation origin of SOC embedded in a mineral matrix. In order for this technique to yield robust results, a large sample set, covering the expected variability in site conditions, is needed in the development and calibration of the spectral regressions and in the independent validation of the spectral model. It will therefore be important to expand our library of aspen- and conifer-derived spectra against which soils from mixed stands will then be compared, beyond those derived from the original few Northern Utah sites. For this project, we propose using soil samples from pure and mixed aspen-conifer sites collected throughout the state as part of other ongoing research projects. We have developed a pre-treatment protocol of soil subsamples with NaOCl at room temperature to remove the SOC while maintaining intact clay structures, using a modification of the method described in Kaiser et al (2002). Once stripped of SOC, the spectral signature of the mineral matrix can determined. We will build on this initial collaboration, and perform spectral analysis (NIRS) on intact soil and mineral matrix (post NaOCl treatment) samples from pure and mixed stands, followed by subtraction of site-specific matrix spectra to obtain the true signature of the SOC for a given forest type and geographic setting. The calibration, cross validation and independent validation of aspen- and coniferderived SOC in mixed aspen-confer forest soils will done with the use of OPUS software, as described in Gruselle and Bauhus (2010).

Progress 07/01/11 to 06/30/16

Outputs
Target Audience:Target Audience scientific community; foresters, managers, landowners Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Opportunities As part of this project, the PI mentored two PhD students (Mercedes Roman-Dobarco, Antra Boca), supported the independent research of one undergraduate student (Brian Rozick), and provided experiential learning to numerous work study students, one high-school student transitioning to college (worked as a laboratory technician), and three summer interns were involved with the sample processing and analysis as method development. How have the results been disseminated to communities of interest?Dissemination To the scientific community: Several presentations by the PI and her graduate students at international and national scientific meetings have resulted from this project: 12th North American Forest Soils Conference, Whitefish, MT (2013, 2 posters); 8th International BIOGEOMON conference, Bayreuth, Germany (2014; 1 poster): the 2014 IUFRO World Congress, Salt Lake City, UT (2014, 1 poster); Soil Science Society of America Annual Meeting, Long Beach CA (2014, invited talk - best presentation award); Annual Meeting of the American Geophysical Union. San Francisco, CA (2014, 1 poster); 5th International Symposium on Soil Organic Matter, Goettingen, Germany (2015, 1 poster, 1 talk); Utah State University Student Research Symposium (2016, 1 poster - Graduate Student Poster Award in Life Sciences); Annual Meeting of Soil Science Society of America, Phoenix, AZ (2016 -accepted, rapid talk); Annual Meeting of the American Geophysical Union. San Francisco, CA (2016 - planned, 1 poster). Several publications in peer reviewed journals have been published (Soil Science Society of America Journal), are under review (Geoderma) or are in preparation (Forests) for dissemination to the scientific community. To Landowner, Land managers: The PI contributed a popular article in Tremblings, the electronic newsletter of the Western Aspen Alliance [http://www.western-aspen-alliance.org/] which targets landowners and agency managers with an interest in aspen. General Public The PhD student participated in a Utah 4-H career workshop for 7th graders in April, 2016, giving 10 minute lectures on SOM research. The presentations took place in our laboratory with groups of 7th graders visiting the lab on their campus tour. The topics addressed related to how the C cycle works, why it matters, methods for soil sampling, laboratory processing and analysis of samples. The object of most interest was a LICOR CO2 analyzer normally used for measuring CO2 in a biomarker incubation experiment. It showed in real-time how the CO2 level rises when a person breathes next to it, hence allowing the children to visualize something abstract that is normally hidden from their view. In addition, the PhD student was one of nine featured student speaker in USU's IGNITE Event, as part of USU's Research Week in April 2016. She gave a 5 minute presentation about the role of soils, which was seen by a wide campus audience. The video of the presentation has since been published on YouTube and has had 387 views since May 2016. What do you plan to do during the next reporting period to accomplish the goals?Plan of Work The PhD student will continue her data analysis as part of her dissertation research. We are currently preparing a manuscript on the C storage and fluxes in aspen and conifer soils that is to be submitted to the journal Forests end of August, 2016, for a special issue on forest nutrient cycling. A manuscript on the sorption experiment is planned for end of 2016, after the experiment is completed. Both of these manuscripts will be part of the dissertation of the current PhD student. The PhD student will prepare a fourth chapter on biomarker use and degradation and defend Spring 2017.

Impacts
What was accomplished under these goals? Accomplishments Field and laboratory studies as part of the graduate research of two doctoral students (one completed in 2014; one ongoing) have mainly focused on elucidating the differences in SOC stabilization and, more recently, determining the role of root- vs litter-derived C in SOC storage and stabilization in aspen and conifer soils (Obj. 1 a, b, d). Field work in northern Utah (T. W Daniel Experimental Forest - TWDEF) and in southern Utah (Cedar Mountain - CM) has largely been completed. This work included recording of stand characteristics (tree diameter and tree height, understory cover) in support of Obj 2a; soil and root sampling; litterfall collection, rhizotron image collection for the growing-seasons of 2015 and 2016 (ongoing); soil pore water sampling during the snowmelt period of 2014, 2015, and 2016 in support of Obj 1a and 1b. We have finished several laboratory analyses to describe SOC stability and its controlling factors (Objective 1): i.SOC quality with depth under each forest type using different analytical approaches, including - C and N concentration in bulk soil, C concentration in three SOC fractions [labile ("free" organic matter) and stabilized (mineral associated, MoM) associated with particles of < and > 53 µm in diameter ]; hot water extractions of labile C; root- and foliage-specific biomarker extraction and analysis with gas chromatography-mass spectrometry; ii.abiotic controls - bulk density, stoniness, soil texture, Fe and Al oxide concentration, clay mineralogy, pH, soil moisture; iii.biotic controls - root picking to determine root mass, C and N concentration in litterfall and roots, dissolved organic carbon (DOC) and nitrogen concentration in snow and soil pore water. The sorption experiment testing the differences of sorption and desorption of aspen and conifer foliage and roots derivatives to mineral surfaces (Obj 1 a) is still ongoing. The data gathered through field and laboratory work have undergone quality checks, and have been used to calculate C fluxes in aspen and conifer forests. These results are currently being summarized in a journal article to be submitted for publication in Fall 2016. -We confirmed previous findings of higher total SOC stocks under aspen compared to conifer and mixed stands (n.s.), and increases in % mineral-associated SOC (MoM) with increasing abundance of aspen in mixed stands (expressed as % of live basal area), suggesting greater stability of SOC with the presence of aspen. -Texture was found to be an important factor controlling stable SOC storage in areas with high (> 70%) clay+silt contents; at sites with 40-70% clay+silt contents, vegetation exerted a greater influence. -We also found higher % Fe and Al in soils from Southern Utah compared to Northern Utah. The higher concentration of Fe and Al correlates with higher % C, helping to explain higher SOC stocks observed in S Utah. -When targeting areas for belowground carbon storage, both edaphic and vegetation factors should be considered in vegetation management. -C flux input quantification indicates that (1) aspen forests have higher aboveground C input associated with leaf litterfall compared to conifers, (2) conifers have more fine root (<2mm) mass than aspen, (3) C balance calculations suggest that aspen have higher root turnover compared to conifers. Fine roots are considered to be the major belowground C input through annual turnover. Vegetation differences in root mass vs annual turnover confound the role of roots in SOC stabilization. -DOC chemistry of percolating soil solutions, as determined with specific ultraviolet absorbance, did not differ between aspen and conifer soils. However, solutions have generally higher C/N ratio under conifers (18-48 under aspen vs 22-61 under conifers), consistent with the higher C/N ratio in conifer needles compared to aspen foliage. -DOC input with snowmelt water and DOC flux at 5 and 45 cm depth differed with vegetation type and collection year. DOC flux at 5 cm and 45 cm was higher under conifers in 2014 and 2015. In 2016, however, the DOC concentrations at 5 cm depth were similar among vegetation types, but aspen had higher C transport with snowmelt water at this depth. -In 2014 and 2015 conifer soils retained more DOC-C in the top 40 cm soil column than aspen. In 2016 the opposite pattern was observed. The reasons for these different DOC flux patterns under aspen are still unclear. By comparison, under conifers only slight fluctuation in DOC concentrations were recorded between all three sampling years. Overall, the differences in concentrations measured in soil pore water carbon were too small to explain the differences in SOC pools under aspen and conifers. To further investigate differences in SOC stability with vegetation cover, the PhD student has sought additional financial support to investigate the use of foliage- and root-specific biomarkers in the various soil fractions. The graduate student received a USU Dissertation Enhancement grant to specifically investigate potential differences in persistence among biomarkers in the soils. So far, we have identified 6 foliage-specific cutin-derived compounds (for aspen leaves and conifer needles combined) and 15 root-specific suberin-derived compounds (aspen and conifer roots combined). The presence of these foliage and root biomarkers in the clay and silt fraction was variable, suggesting that their stability in soil may also be variable. The current available knowledge on biomarker degradation rates in soils is still very limited, and results from this new experiment will provide greater insights into biomarker decay dynamics, which can substantially influence their validity and accuracy as source indicators.

Publications

  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Rozick, B. (Presenter & Author), Van Miegroet, H., Research on Capitol Hill, "Soil Organic Carbon as the Basis for Assessment of Site Condition in Stands of Quaking Aspen," UT Legislature, UT Capitol, Salt Lake City. (January 26, 2016)


Progress 10/01/14 to 09/30/15

Outputs
Target Audience:Target Audience foresters, managers, landowners Changes/Problems:Changes/Problems No changes in research objectives Problems: throughout the year we experienced equipment failure/problems in the SOC and DOC analysis which necessitated multiple sample reruns and caused an overall slowdown in data generation. What opportunities for training and professional development has the project provided?Opportunities As part of this project, the PI mentored one PhD students (Antra Boca), supported the independent research of one undergraduate student (Brian Rozick), and provided experiential learning to two work study students and two summer interns involved with the sample processing and analysis as method development. How have the results been disseminated to communities of interest?Dissemination The former PhD student and the current PhD student presented findings from this research project at the 5th International Symposium on Soil Organic Matter that took place in September, 2015 in Goettingen, Germany. One journal article on the use of Fourier Transform Infrared Spectroscopy to characterization of SOC chemical functional groups in bulk soils, light fraction, MoM was submitted as part of the above international conference. In addition, a report on the specific results from Cedar Mountain site was provided to our extension officer for dissemination to the landowners. What do you plan to do during the next reporting period to accomplish the goals?Plan of Work In the coming year we will continue to focus on differences in stabilization between root-derived vs litter-derived organic compounds (Obj. 1 a & b) and the role of source substrate chemistry vs soil matrix properties (Obj 1d) on SOC stabilization, including laboratory experiments to determine (1) the fate and persistence of foliage vs root-derived biomarker; (2) adsorption of root- and foliage-derived DOC to soils. In addition, soils will be analyzed for aluminum oxides to evaluate the effect of soil mineralogy on SOC quantity and stability. We will continue to disseminate information to the scientific community via peer-review journal articles and to the land managers and landowners via meetings, workshops and targeted reports (Obj 1a, b, d & Obj 2a): - Several presentations by the graduate student are planned at national and international meetings (Obj 1a-d, Obj 2a-b) - Undergraduate student will present his work before Utah Legislatures via "Posters on the Hill" in January 2016. - We plan on drafting and submitting several manuscripts for publication, including describing C pools and fluxes in aspen and conifer soils at TWDEF and CM; and the role of SOC as an indicator of site quality and forest health (aspen regeneration success). - We will continue data analysis for the biomarker and adsorption experiments.

Impacts
What was accomplished under these goals? Accomplishments We continue to make progress towards determining pathways of soil organic carbon (SOC) stabilization in forest soils and assess the relative role of roots and foliage in creating differences in SOC persistence among forest covers (Obj. 1 & 2). 1. A doctoral student is continuing field and laboratory studies focusing on the role of root- vs litter-derived C in SOC storage and stabilization in aspen and conifer soils (Obj. 1 a, b, d). The following activities were conducted at T.W. Daniel Experimental Forest (TWDEF) in N. Utah (intensive aspen and conifer measurement site, 6 plots) and Cedar Mountain (CM) in S. Utah (measurements across aspen-conifer ecotone, 8 plots): - Soil cores were taken to a depth of 50 cm (in 10-cm increments) in N. and S. Utah. Soils were analyzed for total C and distribution into labile (light fraction) and stabilized (mineral associated, MoM) SOC fractions; and for iron oxides, texture and clay mineralogy to evaluate the abiotic soils effect on SOC stabilization. The microbial availability (lability) of C in bulk and SOC soil fractions was approximated using hot water extracts (HWEOC). We had earlier found good correlation between decay during long-term incubation and this fast lab technique. - Carbon inputs via foliar litterfall were determined at TWDEF using littertraps; root abundance and C input were estimated from root cores from each plot at TWDEF and CM and with 30 minirhizotrons (to monitor root distribution and demographics) at TWDEF. Hydrological C fluxes through the soil during snowmelt were determined from dissolved organic carbon (DOC) collected with 12 soil pore water samplers at TWDEF (@ 5 and 45 cm depth) - To determine the contribution of roots vs leaf litter in SOC stabilization, the student has identified foliage- and root-specific monomers for aspen and conifer and analyzed the bulk soils, as well as the silt and clay fraction for these biomarkers. - We are developing an operating procedure for experimentally testing the sorption on mineral surfaces of DOC derived from aspen and conifer roots and foliage (Obj 1 a & b) - we are still in the experimental phase of this experiment and have not results to report We confirmed previous findings of higher total SOC stocks under aspen compared to conifer and mixed stands (n.s.), and increases in % Mineral-associated SOC (MoM) with increasing abundance of aspen in mixed stands (expressed as % of live basal area), suggesting greater stability of SOC with the presence of aspen. We also found higher % Fe in soils from S. Utah compared to N. Utah, which help could explain higher SOC stocks observed earlier in S. Utah. C flux input quantification indicates that aspen forests have higher aboveground C input due to higher leaf litterfall compared to conifers, whereas conifers have more fine root (<2mm) mass than aspen. Fine roots are considered to be the major belowground C input with annual turnover rates. DOC chemistry of percolating soil solutions, as determined with specific ultraviolet absorbance, did not differ between aspen and conifer soils. DOC input with snowmelt water and DOC flux 5 and 45 cm depth was higher under conifers. This observation combined with the lower SOC stocks in conifer soils, suggests that this greater hydrological C influx is not stabilized in the soil. So far we have identified 6 foliage-specific cutin-derived compounds (for aspen leaves and conifer needles combined) and 15 root-specific suberin-derived compounds (aspen and conifer roots combined). The presence of these foliage and root biomarkers in the clay and silt fraction was variable, suggesting that their stability in soil may also be variable. The graduate student is currently exploring additional funding sources to investigate potential differences in persistence among biomarkers in the soils. The current available knowledge on biomarker degradation rates in soils is still very limited, and results from this new experiment will provide greater insights into biomarker decay dynamics, which can substantially influence their validity and accuracy as source indicators. 2. To investigate the influence of forest condition and management on SOC storage and stability under aspen (Obj 2 a), we sampled soils (0-15; 15-30 cm) in several locations at CM and the Dixie National Forest in S. Utah and recorded aspen stand characteristics (including live basal area, % aspen in the overstory, and aspen regeneration success) As part of an undergraduate research project the nutrient supplying capacity of these soils was determined during a laboratory experiment using exchange resins (PRS probes). In addition, stand data were collected from fourteen adjacent aspen and conifer plots in Southern and Northern Utah. The preliminary analysis of this data indicates that SOC is a good surrogate for nutrient supplying power of the mineral soil, especially for nitrogen and some base cations (e.g., Ca). In some cases, the there is an inverse relationship between SOC and nutrient (e.g., P and K), or no correlation (e.g., S). The positive relationship between SOC and nitrogen is robust and valid across soil depths, forest cover and aspen forest condition, lending support for its use as an indicator of soil/site quality. Correlation matrices indicated that nature of the relationships between SOC and nutrient availability determined with PRS probes was similar when SOC concentration (% in fine fraction) or SOC content (Mg/ha) were used, suggesting the SOC concentration is an adequate and useful indicator.

Publications

  • Type: Other Status: Published Year Published: 2015 Citation: Refereed Journal Articles Hansen, M. E., Amacher, M. C., Van Miegroet, H., Long, J. N., Ryan, M. G. (2015). Carbon dynamics in central U.S. Rockies lodgepole pine type following mountain pine beetle outbreaks. Forest Science, 61, 665-679.
  • Type: Other Status: Published Year Published: 2015 Citation: Refereed Journal Articles Uribe, C., Inclan, R., Hernando, L., Roman, M., Clavero, M.A., Roig, S., Van Miegroet, H. (2015). Grazing, tilling and canopy effects on carbon dioxide fluxes in a Spanish dehesa. Agroforestry Systems, 89, 305-318.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2015 Citation: Presentations Roman Dobarco, M. (Presenter & Author), Van Miegroet, H. (Author Only), Jacobson, A. (Author Only), 5th International Symposium on Soil Organic Matter, "Organo-mineral interactions promote greater soil organic carbon storage under aspen in semi-arid montane forests from Utah.," Georg-August-University G�ttingen, G�ttingen, Germany. (September 20, 2015 - September 24, 2015)
  • Type: Conference Papers and Presentations Status: Other Year Published: 2015 Citation: Presentations Boca, A. (Presenter & Author), Hatten, J. (Author Only), Van Miegroet, H. (Author Only), 5th International Symposium on Soil Organic Matter, "The relationship between tree above- and belowground C inputs and cutin and suberin presence in soil.," Georg-August-University G�ttingen, G�ttingen, Germany. (September 20, 2015 - September 24, 2015).
  • Type: Conference Papers and Presentations Status: Other Year Published: 2015 Citation: Presentations Rozick, B. (Presenter & Author), Van Miegroet, H., USU Student Research Symposium, "Soil Organic Carbon as the Basis for Assessment of Site Condition in Stands of Populus tremuloides," USU-RGS, Logan, UT. (April 9, 2015).


Progress 10/01/13 to 09/30/14

Outputs
Target Audience: Target Audience Researchers, forest managers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Opportunities As part of this project, the PI mentored two PhD students (Mercedes Roman Dobarco, Antra Boca) and several undergraduate students in the Quinney College of Natural Resources. It supported the independent research of one undergraduate student (Brian Rozick), and provided experiential learning to three work study students involved with the sample processing and analysis. How have the results been disseminated to communities of interest? Dissemination The two PhD students published three papers in peer-reviewed journals: one on the hardwood-conifer meta-analysis results, two papers on differences in storage and stabilization of SOC along an aspen-conifer ecotone. In addition, results from this research project were presented as posters at the 8th International BIOGEOMON Conference in Bayreuth, Germany and at the 24th IUFRO World Congress in Salt Lake City, Utah. These international conferences take place every 3-4 years and convene forest soil scientists from all over the world. Both conferences had specific sessions on belowground SOC dynamics in forest ecosystems. In addition a report on the results from Cedar Mountain site was provided to our extension officer for dissemination to the landowners. What do you plan to do during the next reporting period to accomplish the goals? Plan of Work Research Objectives that will be addressed in the coming year are: Objective 1 a&b: Investigate differences in stabilization between root-derived vs litter-derived organic compounds Objective 2a: Investigate SOC dynamics in mixed aspen-conifer forest soils and the relationship between SOC dynamics and stabilization and overstory vegetation characteristics - Several field and laboratory experiments will be conducted to determine (1) the presence of root and foliage biomarkers in bulk soil, SOC fractions and DOC; (2) adsorption of root- and foliage-derived DOC to soils (Obj 1a,b). - Soil samples taken will be analyzed for SOC fractions to further assess the relationships forest condition and management on SOC storage and stabilization below the surface (i.e., 0-50 cm depth) (Obj 2a). - Several presentations are planned at national and international meetings (Obj 1a-d, Obj 2a-b). - We will continue to disseminate information to the scientific community via peer-review journal articles and to the land managers and landowners via meetings, workshops and targeted reports (Obj 1a-c, Obj 2a-b).

Impacts
What was accomplished under these goals? Accomplishments We continue to make progress towards determining pathways of soil organic carbon (SOC) stabilization in forest soils and assess the role of abiotic (soils) vs. biotic (vegetation) in creating differences in SOC persistence among forests (Obj. 1 & 2). 1. One PhD student defended her dissertation on the influence of stand composition on SOC stabilization and biochemistry in aspen and conifer forests, using soil samples taken in northern (Franklin Basin) and southern Utah (Cedar Mountain, CM). Major findings from her research are (Obj. 1.a, 2.a, 1.d): - In the upper soil (0-15 cm) there was no vegetation effect on total SOC storage, SOC decomposability, or relative distribution among SOC fractions. - Mineral-associated SOC (MoM) content was higher under aspen than under mixed and conifer cover; solubility of SOC decreased with increasing dominance of aspen, suggesting greater stability of SOC with the presence of aspen. - MoM was inversely correlated with SOC decomposability and solubility, suggesting that organo-mineral interactions reduced biological availability of SOC. - Texture influenced SOC stabilization. With increasing percentage silt+clay, SOC decomposability and solubility declined, and MoM content increased, emphasizing the role of site and soil characteristics on SOC stabilization. - Across the entire data set, texture was a more important factor controlling stable SOC storage at high clay+silt contents, whereas at 40-70% clay+silt contents vegetation exerted a greater influence. The latter sites should be targeted for active vegetation management. - Characterization of SOC chemical functional groups with Fourier Transform Infrared Spectroscopy revealed that across all sample types (bulk soils, light fraction, MoM) there were only subtle qualitative shifts with forest cover, suggesting initial differences in litter chemistry between aspen and conifers converged into similar chemical composition within sites. There were small quantitative differences with forest cover: aspen soil samples/fractions generally had higher polysaccharides and C-O functional groups than mixed and conifer soils. - Collectively these results suggest that chemical stabilization by adsorption of simple molecules, rather than recalcitrance, is the main mechanism of SOC protection under aspen (Obj. 1.a, 2.a, 1.d). 2. Outcomes from an undergraduate research project, conducted on a subset of soil samples from CM, revealed no measurable differences in microbial biomass or microbial functional diversity (indicated by Biolog substrate consumption assay). Thus, differences in SOC stability with vegetation cover are controlled by bio-physical characteristics restricting microbial access, not by absence of critical microbial decomposer groups (Obj. 1.c). 3. A meta analysis of SOC storage in forest floor and mineral soil of conifers and hardwood forests (77 studies in 28 countries) was published in a peer-reviewed journal article. Overall, SOC content of conifer forest floors is 38% higher than in adjacent hardwood stands; mineral SOC stocks were similar. Variability in forest floor SOC had limited predictive power for mineral soil SOC, suggesting that both SOC pools follow different accumulation patterns and are under different controls. precipitation, stand age differences, soil texture and prior landuse differentiate SOC accumulation patterns between hardwoods and conifers when forest floor SOC stocks were compared among genera; with differences in forest floor SOC pools between conifers and hardwoods bigger on colder drier sites than on warmer moister sites and more pronounced when stands had been converted from agricultural land vs. those previously under forest cover. Analysis with seven of the most reported genera showed more pronounced variability in mineral SOC compared to the aggregate comparison. Picea was the only conifer that stored significantly more C than adjacent hardwoods and Eucalyptus was the only hardwood that stored more C than adjacent conifers. Overall the results suggest that when managing forests for SOC storage, species choice may be more critical during afforestation than forest conversion (Obj. 2.a) 4. A doctoral student has started field and laboratory studies focusing on the role of root- vs litter-derived C in SOC storage and stabilization in aspen and conifer soils (Obj. 1 a, b, d). The following activities were conducted: - Soil cores were taken to a depth of 50 cm (10-cm increments) in eight adjacent aspen and conifer plots at CM in S. Utah and in six plots in the T.W. Daniel Experimental Forest (TWDEF) in N. Utah. These samples are currently being analyzed for various SOC fractions. - Foliage and root material has been gathered using littertraps and soil root cores at TWDEF. Roots are currently being separated and cleaned to estimate the overall differences in root mass under both overstories and for use in lab experiments on sorption patterns of root and foliage C from aspen and conifer sources. - Additional soil pore water samplers (to record soil water DOC composition during snowmelt) and additional minirhizotrons (to monitor root distribution and demographics) were installed. First solution samples and minirhizotron images are being analyzed - this task will continue through the coming year. 4. To investigate the influence of forest condition and management on SOC storage and stability under aspen, we sampled soils (0-15; 15-30 cm) in several locations at CM and recorded stand characteristics. As part of an undergraduate research project the nutrient supplying capacity of these soils was determined during a laboratory experiment using exchange resins. The lab work is completed and the data analysis is ongoing. Results from this experiment will inform the role of SOC storage in soil productive capacity (Obj. 2.a).

Publications

  • Type: Other Status: Published Year Published: 2014 Citation: Periodicals Van Miegroet, H. (2014). In Paul Rogers (Ed.), Aspen soil - The dynamic world below the surface (4th ed., vol. 5, pp. 2-3). Tremblings. www.western-aspen-alliance.org/
  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Refereed Journal Articles Boca, A., Van Miegroet, H., Gruselle, M.-C. (2014). Forest overstory effect on soil organic carbon storage  a meta-analysis. Soil Science Society of America Journal, 78, S35-S47.
  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Roman-Dobarco, M., Gruselle, M.-C., Van Miegroet, H., Bauhus, J. (2014). Predicting Tree Species Origin of Soil Organic Carbon with Near-Infrared Reflectance Spectroscopy. Soil Science Society of America Journal, 78, S23-S34.
  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Roman-Dobarco, M., Van Miegroet, H. (2014). Soil Organic Carbon Storage and Stability in the Aspen-Conifer Ecotone in Montane Forests in Utah. Forests, 5(4), 666-688.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2014 Citation: Presentations Van Miegroet, H. (Presenter & Author), Dobarco, M. R. (Author Only), American Geophysical Union Annual Meeting, "Organo-mineral interactions promote greater soil organic carbon storage under aspen in semi-arid montane forests in Utah," American Geophysical Union, San Fransisco, CA. (December 15, 2014 - December 19, 2014)
  • Type: Conference Papers and Presentations Status: Other Year Published: 2014 Citation: Van Miegroet, H. (Presenter & Author), ASA-CSSA-SSSA Internatioanl Annual Meeting, "Soil Organic Carbon - an old story with and new future," Soil Science Society of America, Long Beach, CA. (November 2, 2014 - November 5, 2014)
  • Type: Conference Papers and Presentations Status: Other Year Published: 2014 Citation: Boca, A. (Presenter & Author), J., Van Miegroet, H. (Author Only), 24th IUFRO World Congress, "Foliage and root contribution to SOC pools in Utah forest soils," Internatioanl Union of Forest Research Organization and Society of American Foresters, Salt Lake City, Utah. (October 5, 2014 - October 11, 2014)
  • Type: Conference Papers and Presentations Status: Other Year Published: 2014 Citation: Dobarco, M. R. (Author Only), Van Miegroet, H. (Presenter & Author), 8th International Biogeomon Conference, "SOC dynamics in aspen and conifer soils in montane forests in Utah. USA.," University of Bayreuth, Bayreuth, Germany. (July 13, 2014 - July 17, 2014)


Progress 01/01/13 to 09/30/13

Outputs
Target Audience: researchers, forest managers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? As part of this project, the PI mentored two PhD students and several undergraduate students in Natural Resources. It supported the independent research of two undergraduate students; formed the framework for a capstone experience for a Interdisciplinary Studies major, and provided experiential learning to two to three work study students involved with the sample processing and analysis. How have the results been disseminated to communities of interest? The two graduate students presented part of their dissertation research as posters at the 12th North American Forest Soils Conference in WhiteFish, Montana. This international conference takes place every 4 years and convenes forest soil scientists and managers from Europe, Australia, New Zealand and North America to discuss emerging issues in forest management. This year’s focus was on role of forest soils in sustaining Ecosystem Services, including mitigation of greenhouse gas emissions. Results generated two manuscripts that were submitted for publication in the Soil Science Society of America Journal, and are currently under review. What do you plan to do during the next reporting period to accomplish the goals? Research Objectives addressed in the coming year are: Objective 1: Determine SOC stability in aspen forest soils a.Investigate role of adsorption to the soil mineral surfaces as SOC stabilization mechanism? b.Investigate differences in stabilization between root-derived vs litter-derived organic compounds? c.Investigate relationship between chemistry of C inputs and soil protection Objective 2 Investigate SOC dynamics in mixed aspen-conifer forest soils? a.Investigate whether SOC dynamics and stabilization can be predicted from vegetation characteristics b.Investigate whether changes in SOC storage and dynamics occur gradually or stepwise (critical threshold)? - Tasks related to SOC storage and distribution in mixed aspen-conifer stands and the spectroscopic analysis (FTIR and NIRS) will be completed as part of a PhD dissertation (defense summer 2013) and will be prepared in several manuscripts (Obj 1c, Obj 2a-b) - Several field and laboratory experiments will be conducted to determine (1) the presence root and foliage biomarkers in bulk soil, SOC fractions and DOC; (2) adsorption of root- and foliage-derived DOC to soils (Obj 1a-c). - Soil samples taken will be analyzed for SOC, readily decomposable (HWEOC), light fraction and mineral-associated SOC, to further assess the relationships forest condition and management on SOC storage and stabilization (Obj 2a-b). - Several presentations are planned by students involved in the project at national and international meetings (Biogeomon Conference, American Geophysical Union, IUFRO World Congress etc) (Obj 1a-c, Obj 2a-b). - We will continue to disseminate information to the scientific community via peer-review journal articles and to the land managers and landowners via meetings, workshops and targeted reports (Obj 1a-c, Obj 2a-b) .

Impacts
What was accomplished under these goals? We have made significant progress towards our overaching goal of determining pathways of soil organic carbon (SOC) stabilization in forest soils and assess the role of abiotic (soils) vs. biotic (vegetation) in creating differences in SOC persistence among forests (Objective 1 & 2). 1. To investigate the influence of forest overstory composition on SOC storage and stability, we sampled soils (0-15 cm) in plots and transects located along the transition between aspen and conifer forests in Northern and Southern Utah. Major findings are: - Potential decomposability of SOC indicated by hot water extractable SOC (HWEOC) is positively correlated to cumulative CO2 released in laboratory incubations (10 months), suggesting that labile, or potentially decomposable SOC, can be approximated more efficiently by less time consuming hot water extractions. - In the top 15 cm of the mineral soil SOC storage does not change significantly along the aspen-conifer ecotone. Specifically at our Southern Utah site, soil texture seems to play a more important role in SOC stabilization in the topsoil than vegetation cover. Microbial decomposition of SOC decreases with increase on silt + clay content, suggesting that SOC persistence is improved by chemical stabilization of SOC. - Potential decomposability of SOC indicated by HWEOC per C unit in the soil is negatively correlated with aspen live basal area (LBA %), suggesting that aspen-derived SOC may be less decomposable, i.e., less available to microbes. - Characterization of SOC chemical functional groups with Fourier Transform Infrared Spectroscopy (FTIR) is still ongoing, but initial analysis of the data shows that the chemical composition of the light fraction (LF) differs by vegetation cover. The LF-SOC in aspen soils is distinct, with higher concentration of C-O functional groups (e.g., ester, ether, phenols, and polysaccharides) while the chemistry of the mixed and conifer soils LF is similar, probably due to the slower decomposition of conifer needles. The chemical composition of the mineral-associated SOC fraction varies more among sampling sites than by vegetation type, suggesting control of mineralogy on the bonding of SOC to mineral (clay+silt) particles. - Near-infrared reflectance spectroscopy (NIRS) was used to develop prediction models for identifying the species origin of SOC in mixed aspen-conifer soils. NIRS models showed good prediction ability at the validation step, but the influence of site-specific factors on spectral properties decreased model performance during independent validation. Thus, NIRS shows potential for predicting the signature of vegetation on SOC; however, models should be calibrated for soils of similar texture and parent material to increase prediction power. Findings have been submitted as a manuscript for publication. 2. Meta-analysis on the differential influence of vegetation types (hardwoods vs conifers) on SOC storage was completed using 77 studies from 28 countries. Forest floor C stock was the only variable that showed a significant difference, being higher in conifer than hardwood stands. The SOC stocks in the mineral soil were similar irrespective of soil depth, but some patterns could be discerned when data were organized by genus. Results were submitted as a manuscript for publication 3. As part of her doctoral research, a second graduate student has started field and laboratory studies focusing on the role of root-derived vs litter-derived carbon in causing differences in SOC storage and stabilization between aspen and conifer soils (Objective 1 a, b, d). The following activities were conducted: - Soils samples were taken to a depth of 50 cm (in 10-cm increments) and stand characteristics were recorded in a total of 12 plots located at Cedar Mountain in S. Utah (4 aspen and 4 conifer) and in the T.W. Daniel Experimental Forest (TWDEF; 2 aspen and 2 conifer ) in N. Utah. Soils are current being processed to determine bulk density, total SOC and distribution over readily decomposable (HWEOC), light fraction and mineral-associated SOC. Soils will be used for dissolved organic carbon (DOC) adsorption experiments in the lab. - In 2 aspen and 2 conifer plots at TWDEF we installed 8 soil pore water samplers to record soil water DOC composition during snowmelt; 24 minirhizotrons to monitor root distribution and demographics; and 20 littertraps to collect foliar carbon inputs. - 20 aspen and 20 Engelmann spruce saplings were grown in the greenhouse in preparation for 13C enrichment experiment. - aspen saplings were grown in pots to generate litter and root substrate for the analysis of root and foliage chemical biomakers. 4. To investigate the influence of forest condition and management on SOC storage and stability under aspen, we sampled soils (0-15; 15-30 cm) in several locations at Cedar Southern Utah and recorded stand characteristics. Soils are current being processed to determine bulk density, total SOC and distribution over readily decomposable (HWEOC), light fraction and mineral-associated SOC.

Publications

  • Type: Journal Articles Status: Published Year Published: 2013 Citation: Uribe, C., Inclan, R., Sanchez, D.M., Clavero, M.A., Fernandez, A.M., Morante, R., Cardena, A., Blanco, A., Van Miegroet, H. (2013). Effect of wildfires on soil respiration in three typical Mediterranean forest ecosystems in Madrid, Spain. Plant and Soil, 369, 403-420.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2013 Citation: Dobarco, M. R. (Presenter & Author), Van Miegroet, H. (Author Only), Jacobson, A. (Author Only), Gruselle, M.-C. (Author Only), Bauhus, J. (Author Only), 12th North American Forest Soils Conference, "The use of spectroscopic techniques to determine overstory species influence on SOC properties and origin," Whitefish, Montana. (June 17, 2013 - June 20, 2013)
  • Type: Conference Papers and Presentations Status: Other Year Published: 2013 Citation: Boca, A. (Presenter & Author), Dobarco, M. R. (Author Only), Van Miegroet, H. (Author Only), Gruselle, M.-C. (Author Only), Michalzik, B. (Author Only), Fernandez, I. (Author Only), 12th North American Forest Soils Conference, "Linking overstory, soil and climate characteristics to explain C storage in forest soils  a meta-analysis," Whitefish, Montana. (June 17, 2013 - June 20, 2013)


Progress 01/01/12 to 12/31/12

Outputs
OUTPUTS: Activities The objective of this project is to investigate the influence of biotic vs. abiotic factors on soil organic carbon (SOC) persistence in aspen-conifer forest ecotones. Field soil samples were taken in mixed aspen-conifer stands on Cedar Mountain in Southern Utah to ascertain how the amount and persistence of SOC changes as relative proportions of aspen and conifer in the overstory change (Obj 2). Lab assays were conducted to elucidate mechanisms and drivers of SOC stabilization and differences in SOC storage between aspen and conifer soils (Obj 1) including: the role of abundance and composition of the microbial population, the potential adsorption of aspen litter derived soluble C to mineral surfaces, and the determination of chemical composition of this mineral-associated (stable) SOC using mid-infrared spectroscopy. We have also continued our collaboration with the University of Freiburg to discern aspen vs. conifer contribution to SOC in mixed stands, by analyzing soil samples derived from multiple location in Northern and Southern Utah with near-infrared spectral analysis (Obj 2). Dissimination The PI presented the preliminary findings of the field and lab measurements as a poster to the scientific community at the 7th International BIOGEOMON conference in Maine. This conference, which brings together biogeochemists from Europe and North America, focuses on the impacts of environmental change on terrestrial and aquatic ecosystem health and functioning. PARTICIPANTS: Individuals: Principal Investigator - Van Miegroet: project oversight and student mentoring Mercedes Roman-Dobarco: grad student studying changes in soil C properties along aspen-conifer transition, is responsible for field soil sampling in mixed aspen-conifer stands at Cedar Mountain; lab experiments to determine soil C speciation, and NIRS analysis (at University of Freiburg) of aspen and conifer soils from Northern and Southern Utah. Two undergraduate students received support to conducting research experiments on respectively, adsorption of aspen leaf-litter derived DOC and microbial abundance and activity in pure and mixed aspen and conifer soils. Partner Organizations: US Forest Service Utah State Forest (Cedar Mountain) Private landowners in S. Utah University of Freiburg, Germany Collaborators: Marie-Cecile Gruselle (University Maine) Juergen Bauhus (University of Freiburg, Germany) Janis Boettinger, Astrid Jacobson, Jennifer Reeves (USU- Dept Plant, Soils and Climate) Training: This project supported the research of one graduate and two undergraduate students; it has also provided experiential learning to three work study students involved with the sample processing and analysis. Training: This project has supported the research of one graduate and two undergraduate students; it has also provided learning expeience to TARGET AUDIENCES: The target audience for this research is twofold: Basic research: peer community of soil scientists, biogeochemists and carbon modelers (i.e., members Soil Science Society of America, Ecological Society of America, American Geophysical Union), NRCS Management implications: private landowners and agencies involved with the management of natural resources for a diversity of societal values, e.g., U.S. Forest Service, Bureau of Land Management, Natural Resources Conservation Service, Utah Department of Natural Resources etc. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
There is great interest in the capacity of soils to store C as a way to mitigate increasing atmospheric CO2 levels. Also, soil organic matter (which largely consists of SOC) is linked to site productivity and site quality, and may useful as an indicator of management impact. The soils research in mixed aspen-conifer forests at Cedar Mountain in Southern Utah by researchers at Utah State University (USU) has yielded the following results: - The amount of SOC in the mineral soil is positively correlated with nutrient supply rates across a broad range of aspen-conifer forest sites, and may thus be used as an indicator of site quality conditions. - In mixed aspen-conifer stands, there is a positive relationship between the relative abundance of aspen in the overstory, as expressed by stand density index (SDI), and total SOC storage (0-15 cm), but there are significant differences among sites which have not yet been fully elucidated. Thus, not only do soils under pure aspen soils store more SOC than conifer soils, but the beneficial effect of aspen on soil SOC storage capacity also occurs in mixed stands. - We are still in the process of evaluating how differences in SOC levels along a gradient of aspen in mixed forests is reflected in SOC partitioning among labile (microbial, water-extractable, free particulate) and more protected (mineral-associated) SOC pools. Preliminary data show that lower SOC storage capacity associated with the increasing presence of conifers in the overstory (%SDI) is linked to higher microbial abundance and a greater ability of these microbes to metabolize a variety of C substrates - Microbial abundance is not correlated with hot water extractable OC but is positively correlated with the amount of SOC mineralized during the first two weeks of soil incubation. This would indicate that not all measurements currently used in the literature to designate "labile SOC" fully overlap. - The pilot study on the adsorption of soluble DOC compounds derived from aspen litter as a potential SOC stabilization mechanism is still ongoing. USU researchers (PI and graduate student) continued their collaboration with in cooperation with scientists at the University of Freiburg, Germany, on the use of near-infrared reflectance spectroscopy (NIRS) to develop models for identification of aspen and conifer components on soil organic carbon (SOC). The spectral dataset was augmented with a new set of soil samples collected at Franklin Basin (Fall 2011), Deseret Land and Livestock and T.W. Daniel Experimental Forest (Fall 2009) in Northern Utah. The current dataset covers a wider geographical area (northern and southern Utah), enabling us to develop regional models for aspen and conifer SOC. To our knowledge we are first to test this approach for detecting the vegetation origin of SOC in a mineral soil. Soil minerals have their own spectral signal that cannot easily be separated from that of organic matter. Soil pre-treatment at room temperature is used to remove SOC without damaging clay structures and to obtain the spectral signature of the soil matrix. The spectral signature of pure SOC is then obtained through spectral subtraction.

Publications

  • Uribe, C., Inclan, R., Hernando, L., Roman, M., Clavero, M.A., Roig, S., & Van Miegroet, H. 2012. Pature, tillage and canopy effects on carbon dioxide fluxes in a Spanish dehesa: (In Preparation for submission). (In Preparation; Not Yet Submitted).
  • Woldeselassie, M., Van Miegroet, H., Gruselle, M.-C., & Hambly, N., (2012). Storage and stability of SOC in aspen and conifer forest soils of Northern Utah.: Soil Science Society of America Journal, 76: 2230-2240. (Published).
  • Uribe, C., Inclan, R., Sanchez, D.M., Clavero, M.A., Fernandez, A.M., Morante, R., Cardena, A., Blanco, A., & Van Miegroet, H. 2012. Effect of wildfires on soil respiration in three typical Mediterranean forest ecosystems in Madrid, Spain: Plant and Soil. (Accepted).
  • Roman-Dobarco, M., Gruselle, M.-C., Van Miegroet, H., & Bauhus, J. 2012. The use of near-infrared reflectance spectroscopy (NIRS) to determine the contributions of different tree species to SOC: Soil Biology aand Biochemistry (Revision-Expansion). (In Preparation; Not Yet Submitted).