Source: BOISE STATE UNIVERSITY submitted to
AT THE ROOT OF SUSTAINABLE BIOENERGY: USING GENETIC VARIATION IN ROOT TRAITS TO MAXIMIZE SOIL CARBON SEQUESTRATION AND BIOMASS YIELDS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0230875
Grant No.
2012-67010-20069
Project No.
IDAW-2012-00910
Proposal No.
2012-00910
Multistate No.
(N/A)
Program Code
A6125
Project Start Date
Sep 1, 2012
Project End Date
Aug 31, 2016
Grant Year
2012
Project Director
de Graaff, M.
Recipient Organization
BOISE STATE UNIVERSITY
1910 UNIVERSITY DRIVE
BOISE,ID 83725
Performing Department
(N/A)
Non Technical Summary
Land use change for bioenergy production can create substantial green house gas (GHG) emissions through removal of standing vegetation and disturbance of soil carbon (C) pools. A recent body of literature suggests that native species with extensive root systems can rapidly repay the GHG debt, particularly when grown in diverse mixtures, by enhancing biomass production and soil C sequestration upon land-use change. Native bioenergy candidate species, switchgrass (Panicum virgatum L.), also show extensive within-species variation, and our group has collected novel preliminary data showing that increased cultivar diversity can enhance aboveground biomass production. With this proposed project we wish to assess: (1) whether shifting C3-dominated nonnative perennial grasslands to C4-dominated native perennial grasslands repay the C debt of land-use change by increasing soil C sequestration within the early years of establishment; (2) whether increased variation in root traits in species and cultivar mixes of native perennial grasses will enhance biomass production, soil C storage and the efficiency of nitrogen (N) cycling (i.e., decrease N losses); and (3) whether energy gain resulting from an increase in soil C storage and yield, along with a decrease in nutrient inputs and losses in low-input diverse mixtures of perennial grasses, is sufficient to offset energy gain from relatively greater biomass production in high input monocultures of perennial grasses. We will leverage an ongoing experiment conducted at the Fermilab National Environmental Research Park that compares different approaches for perennial feedstock production ranging across a biodiversity gradient, where diversity is manipulated at both the species- and cultivar level, and N is applied at two levels (0 and 67 kg/ha). Ultimately the goal of our proposed project is to evaluate which method of land-use change for bioenergy production maximizes yields, while minimizing the negative impacts of land-use change on the environment. This project will be the first to assess how within-species biodiversity can be used to maximize yields while minimizing inputs to the system, thereby reducing negative impacts of bioenergy feedstock production on the environment. Outcomes of our project can inform resource managers about the potential of a new approach for improving the sustainability of bioenergy feedstock production in the long-term by simultaneously (1) reducing the amount of nutrients needed to produce bioenergy feedstocks and (2) promoting soil quality through enhancement of soil C sequestration. In addition, this approach to bioenergy production will take better advantage of existing germplasm to maximize yields and C sequestration.
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
1020110100050%
1021629107050%
Goals / Objectives
1. To determine if shifting C3-dominated nonnative perennial old-field grasslands to C4-dominated native perennial grasslands directly repay the carbon (C) debt of land-use change by increasing soil C sequestration within the early years of establishment. Outputs: A comparison of total soil C contents in soils of old-fields and in soils converted from old-fields to C4-dominated native perennials. These data will be collected and analyzed in year 1. 2. To determine if increases in root production and stabilization of root derived C in soil upon planting native perennials offset the losses in soil C-input (both above and belowground) from old fields. Outputs: A comparison of root-derived C stabilization in a variety of soil fractions defined by their ability to physically protect soil C in soils of old-fields and in soils converted from old-fields to C4-dominated native perennials. These data will be collected and analyzed in years 2 and 3. 3. To assess whether increased variation in root traits in species and cultivar mixes of native perennial grasses will enhance biomass production and soil C storage. Outputs: (1) A comparison of total soil C contents along a gradient of increasing inter- and intra-specific diversity of native perennials. These data will be collected and analyzed in year 1. (2) A comparison of root-derived C stabilization in a variety of soil fractions defined by their ability to physically protect soil C along a gradient of increasing inter- and intra-specific diversity of native perennials. These data will be collected and analyzed in years 2 and 3. (3) A comparison of biomass production along a gradient of increasing inter- and intra-specific diversity of native perennials. These data will be collected and analyzed in years 2 and 3. 4. To assess whether increased variation in root traits of cultivar mixes of native perennial grasses will increase the efficiency of nitrogen (N) cycling (i.e., decrease N losses). Outputs: Initiation of 15N tracer experiment in year 1 and a comparison of nitrogen use efficiency and N2O emissions along a gradient of increasing switchgrass diversity, which will be conducted in years 2 and 3. 5. To evaluate if the net energy gain resulting from an increase in soil C storage, along with a decrease in nutrient inputs and losses in low-input diverse mixtures of perennial grasses, is sufficient to offset the net energy gain from greater biomass production in high-input monocultures of perennial grasses. Outputs: A life-cycle analysis of C equivalents in fossil fuel inputs required to produce the different bioenergy cropping systems and GHG outputs resulting from the production of the bioenergy crops. This analysis will be conducted in year 3.
Project Methods
The studies will be conducted at the Sustainable Bioenergy Crop Research Facility located at Fermilab National Environmental Research Park (IL). Prior to the experiment (from 1971 to 2007) the site was maintained as an old field dominated by C3 grasses. In spring of 2008 Switchgrass monocultures as well as diversity trials were seeded, with four levels of cultivar diversity (1, 2, 4, 6) and three types of species treatments (switchgrass, big bluestem, or switchgrass+big bluestem polyculture). To assess how land-use change impacts net soil carbon (C) sequestration, we will compare total C contents in soils of C4-dominated native perennial grasslands and in soils of the original C3-dominated old fields, and assess changes in soil C against samples collected at time zero. To assess how biodiversity affects soil C storage, we will measure total C contents in experimental field plots along a biodiversity gradient of between and within-species biodiversity. To determine the importance of native perennial root-derived C inputs for mediating changes in soil C upon land-use change and with increasing biodiversity, we will measure root-derived soil C stabilization in a variety of soil fractions defined by their ability to physically protect soil C. We will use the natural 13C isotopic difference between the native C3 soil and C4 plants to quantify root-derived soil C stabilization. Samples for physical fractionation will be selected based on the results from our total C measurements, where soils that showed both the smallest and greatest changes in soil C upon land conversion and with increases in diversity will be fractionated. In all samples, we will measure standing root biomass. To evaluate whether root trait variability can lead to more efficient nitrogen (N) cycling, we will we will apply a small amount of highly enriched 15N to each experimental field plots and trace the label into the soil mineral and microbial N pools and plant biomass. We will measure N2O production in laboratory incubations. To assess whether a change in N cycling is related to greater co-location of different cultivar roots, we will determine root biomass and use high-throughput genotyping to quantify realized above- and below-ground genotype diversity levels in our experimental system. Finally, we will conduct a life-cycle analysis of C equivalents in fossil fuel inputs required to produce the different bioenergy cropping systems and GHG outputs resulting from the production of the bioenergy crops. We will use ANOVA to assess whether plant treatment affects biomass yields and soil C contents biodiversity alters biomass yields, root density, soil C sequestration or the efficiency of N cycling. The success of the project will be evaluated by the PI and Co-PI's of the project, via monthly meetings that will serve to discuss collected data analyses and general project-progress. PI-de Graaff will develop graduate student seminar series and include discussion/ debate based activities in undergraduate ecology-classes at Boise State University to educate students about biofuel development, its potential impacts on ecosystems and terrestrial-atmospheric C and N cycle feedbacks.

Progress 09/01/12 to 08/31/16

Outputs
Target Audience:Our products reached the international scientific community. We disseminated our work through invited seminars, presentations at conferences, and workgroups. These included: the American Geophysical Union - Annual Meeting (2012, 2013, 2014, 2015), Ecological Society of America Meeting (2015), three annual PD meetings organized by NIFA, University of New Hapshire (seminar), Kellog Biological Station (seminar - set for 2-10-2017). In addition, our work was featured on 'Science Daily' in an article entitled "New recipe for biofuel: Genetic diversity can lead to more productive growth" (https://www.sciencedaily.com/releases/2016/02/160223132805.htm). Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?We have hired a graduate student (Aislinn Johns) to work on this project. In addition, eight undergraduate students have contributed to this project in 2013 and 2014: (1) Jaron Adkins, (2) Mary Finnell. (3) Trevor Thornton, (4) Michael Brucker, (5) Dan Melody, (6) Kaisha Young, (7) Kimberly Tate, (8) Ariane Shannon, (9) Nate Azevedo. Jaron and Mary have presented a poster at the undergraduate research conference at Boise State University on their work, in addition, Jaron Adkins has presented his work at the AGU meetings in San Fransisco in 2013 and Aislinn Johns presented a poster at the AGU in 2015. Jaron is currently a graduate student at Michigan State University, and has received aan NSF-GRFP fellowhip for his research. The reviewers that assessed his GRFP application mentioned that evidence ofhis productivity associated with this project(i.e. he co-authored two articles from our project, he published one paper as first author and is ready to submit another paper as first author)helped him secure his GRFP fellowship (http://www.for.msu.edu/news/article/forestry_doctoral_student_earns_nsf_fellowship). How have the results been disseminated to communities of interest?We have presented results from this project at the AGU annual meetings in San Fransisco (2012, 2013, 2014, 2015, 2016), at the ESA annual meeting in Sacramento (2014), at a DOE workshop (Improved Representation of Roots in Models) at Oak Ridge National Laboratory (2014), at the SOM6 meeting in South Carolina (2014); at the ESA meeting in Baltimore in 2015, and at the CZO-workshop in Lafayette IL in October 2015. We have also presented our results at the AAIC conference in Washington DC (October, 2013), and at the NIFA-PD meeting in 2014 and 2015. de Graaff has further been invited to give a seminar at the Kellog Biological Station (MI) in February 2017, and has been invited to the ASA, CSSA & SSSA International Annual Meetings in Phoenix (Nov. 6-9, 2016) to speak in a symposium entitled: "Unearthing the role of global soil biodiversity in ecosystems". Finally, de Graaff has been invited to speak about this project in a symposium on behalf of the Global Soil Biodiversity Initiative ("From microbes to moles: Diversity in soils support resilience in ecosystem services.") at the ESA meetingin Portland (2017). What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Goal 1: To determine if shifting C3-dominated nonnative perennial old-field grasslands to C4-dominated native perennial grasslands directly repay the carbon (C) debt of land-use change by increasing soil C sequestration within the early years of establishment. Accomplishment: Upon comparing total soil C contents across all of our treatments, we found: (1) converting C3-dominated nonnative perennial old-field grasslands to C4- dominated native perennial grasslands results in a significant soil C debt in the first year after land-use change, (2) this debt is not paid back within the first four years following land-use change, regardless of plant species or plant species richness, however after four years of growth we found that big bluestem tends to accrue soil C at a faster rate than switchgrass; (3) nitrogen fertilizer application (67 kg N/ ha) did not affect soil C sequestration rates four years following land use change (Adkins et al., in prepapration). Goal 2: To determine if increases in root production and stabilization of root derived C in soil upon planting native perennials offset the losses in soil C from old fields. Accomplishment: We found that in the short-term (i.e. up to four years following land-use change) stabilization of root-derived C was not sufficient to offset losses in soil C created by land-use change. We also found that the rate of root-derived C input and stabilization was affected by species and cultivar type. Root-derived C accumulated at a greater rate in soils planted with big bluestem than in soils planted with switchgrass. Root-derived C also acccumulated faster in soils planted with switchgrass cultivars that had a greater specific root length (SRL [root length/ gram root]) (Adkins et al., 2015). Whereas SRL was related to root-derived C in switchgrass soils (0-15 cm)(Adkins et al., 2015), root biomass was not. These data indicate that differences in root traits (i.e. SRL) among cultivars can differentially impact root C input and stabilization, and that root traits are important to consider when optimizing soil C sequestration in bioenergy cropping systems (Adkins et al., 2015). Goal 3: To assess whether increased variation (i.e. diversity) in root traits in species and cultivar mixes of native perennial grasses will enhance biomass production and soil C storage.Output 1:A comparison of total soil C contents along a gradient of increasing inter- and intra-specific diversity of native perennials.Accomplishment:We found that: (1) increased species or cultivar diversity does not affect the rate of soil C sequestration in our experiment, and(2) soils planted with monocultures, or with poly-cultures of big bluestem cultivars accrue C at a greater rate than soils planted with switchgrass or any other species mix (Adkins et al., in preparation). Output 2:A comparison of root-derived C stabilization in a variety of soil fractions defined by their ability to physically protect soil C along a gradient of increasing inter- and intra-specific diversity of switchgrass. Accomplishment: We founddifferences in the quantity of root-derived C in the switchgrass diversity plots. Specifically, in the CPOM fractions, plots planted with 4 switchgrass cultivars had significantly more root-derived C than plots planted with 6 switchgrass cultivars (p = 0.013). In the silt fractions, 2-cultivar plots had more root-derived C than 6-cultivar plots (0.037), and in the clay fractions, 1-cultivar plots had more root-derived C than 2-cultivar plots (p = 0.002). Although there were differences in root-derived C in different fractions among diversity levels, we were unable tofind any consistent patterns that allowed us to conclude that increased diversity in switchgrass increases the stabilization of root-derived C.Output 3:A comparison of biomass production along a gradient of increasing inter- and intra-specific diversity of native perennials.Accomplishment:We found that genotypic mixtures had one-third higher biomass production than the average monoculture, and no monoculture was significantly higher yielding than the average mixture.Further, year-to-year variation in yields was reduced in the mixture of switchgrass relative to the species monocultures. However, the effects of genotypic diversity on biomass composition were modest relative to the differences among genotypes. In conclusion (summary of goal 3): Our data indicate that species impacts on soil C sequestration trump impacts of N fertilization, cultivar type,or diversity level, as revealed by the significantly greater rates of C accrual in soils planted with big bluestem compared to any other treatments. However, soil C accrues slowly, and switchgrass and big bluestem stands mature slowly, thereby limiting soil C inputs. Given that the cultivar mixture consistently outperformed single cultivar yields, we can expect that greater plant-C inputs to soil with greater genetic diversity may allow us to detect diversity-induced increases in soil C sequestration in the future. Goal 4: To assess whether increased variation in root traits of cultivar mixes of native perennial grasses will increase the efficiency of nitrogen (N) cycling (i.e., decrease N losses). Accomplishments: We applied the 15N tracer to 64 of the switchgrass diversity plots in the spring of 2013. In 2014, we have harvested all the plant material from the subplots to which 15N was applied, and have analyzed this plant material for 15N content. We also subjected the roots to genotyping to ascertain that plots with greater plant diversity are diverse belowground. We found significant differences in standing biomass, nitrous oxide emissions and nitrogen use efficiency (NUE) among switchgrass cultivars, but we found no evidence that increasing switchgrass cultivar diversity enhanced NUE, or any other N cycling processes.These results suggest that NUE is not the sole mechanism behind greater biomass production associated with enhanced diversity (Johns - thesis, 2016). Goal 5: To evaluate if the net energy gain resulting from an increase in soil C storage, along with a decrease in nutrient inputs and losses in low-input diverse mixtures of perennial grasses, is sufficient to offset the net energy gain from greater biomass production in high-input monocultures of perennial grasses. Accomplishments: Our results indicate that high-input low-diversity systems produce significantly more biomass (+40% on average), than low-input high-diversity systems. In addition, our data indicated that fertilization or diversity treatments did not affect soil C sequestration. When we compared inputs and outputs between high-diversity low-input and low-diversity high-input systems using C equivalents of fossil fuel input, we found that despite higher emissions of C from fertilizer use and accompanying greater N2O emissions, the high-input low-diversity plots had lower overall GHG outputs owing to the significantly greater biomass production. Despite the fact that the high-input low-diversity treatments outperformed the low-input high-diversity treatments in terms of biomass production, we did find that across the low-input treatments, increasing cultivar diversity enhanced biomass production, and reduced year-to-year variability in yield with no negative impacts on feedstock quality (Morris et al., 2016). Taken together, these findings on biomass yield and composition suggest that genotypic mixtures could be a useful strategy to increase and stabilize yields in biomass feedstock production systems, in parallel with crop improvement efforts. Further studies, especially in marginal production environments and on targeted genotypic mixtures, will help determine the potential value of genotypic mixtures to increase the sustainability and profitability of native perennial bioenergy cropping systems (Morris et al., 2016).

Publications

  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Kardol, P., Throop, H. L., Adkins, J., & de Graaff, M. A. (2016). A hierarchical framework for studying the role of biodiversity in soil food web processes and ecosystem services. Soil Biology and Biochemistry. http://dx.doi.org/10.1016/j.soilbio.2016.05.002
  • Type: Theses/Dissertations Status: Published Year Published: 2016 Citation: Switchgrass cultivar and intraspecific diversity impacts on nitrogen use efficiency. Boise State University. http://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=2176&context=td
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: de Graaff M-A, Jastrow J, Six J, Wullschleger S (2015) Fine root morphology as a driver of root and soil organic carbon decay rate. Ecological Society of America Annual Meeting, Baltimore, MD. Invited.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Adkins J, de Graaff M-A (2015) A meta-analysis of soil biodiversity impacts on the carbon cycle. 57th Annual Symposium of the Idaho Academy of Science and Engineering, Boise, ID.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: de Graaff M-A (2014) Root controls on soil organic matter stabilization and destabilization. The Sixth International Workshop on Soil and Sedimentary Organic Matter Stabilization and Destabilization, Kiawah Island, SC.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: de Graaff M-A (2014) At the root of sustainable bioenergy: using genetic variation in root traits to maximize soil carbon sequestration and biomass yields. USDA-NIFA AFRI Sustainable Bioenergy Annual Project Director (PD) Meeting, Arlington, VA. Invited.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: de Graaff M-A (2014) Root controls on soil organic carbon dynamics. Ecological Society of America Annual Meeting, Sacramento, CA. Invited
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: de Graaff M-A (2013) Root controls on soil organic carbon dynamics. Annual Meeting of the Ecological Soeciety of Germany, Switzerland and Austria, Potsdam, Germany. Invited
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: de Graaff M-A, Morris G, Jastrow J, Six J (2013) At the root of sustainable bioenergy production: using genetic variation in root traits to maximize soil carbon restoration and biomass yields. AAIC 25th Annual Meeting New Crops: Bioenergy, Biomaterials, and Sustainability Washington D.C., 2013. Invited
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: de Graaff M-A (2015) Plant root impacts on soil organic carbon dynamics. Critical Zone Science, Sustainability, and Services in a Changing World, Purdue University, West Lafayette, Indiana.
  • Type: Conference Papers and Presentations Status: Accepted Year Published: 2016 Citation: de Graaff M-A., Adkins J., Throop H., Kardol P (2016) Soil biodiversity impacts on ecosystem processes. ASA-CSSA-SSSA Annual Meeting, Phoenix, AZ.
  • Type: Conference Papers and Presentations Status: Accepted Year Published: 2016 Citation: de Graaff M-A., Johns A., Adkins J., Morris G., Six J., Jastrow J.D (2016) Impacts of root traits and genotypic diversity in switchgrass cropping systems on biogeochemical cycling of soil carbon and nitrogen.
  • Type: Other Status: Other Year Published: 2014 Citation: de Graaff M-A.(2014 Linking plant-soil relations to ecosystem processes in a changing climate. University of New Hampshire  Durham, NH.
  • Type: Other Status: Other Year Published: 2017 Citation: de Graaff M-A.(2017) Impacts of root traits and genotypic diversity in switchgrass cropping systems on biogeochemical cycling of soil carbon and nitrogen. Kellog Biological Station (MI).
  • Type: Conference Papers and Presentations Status: Accepted Year Published: 2012 Citation: Adkins J., de Graaff M-A., Jastrow J.D., Wulschleger S (2012) Switchgrass cultivars differentially affects soil carbon stabilization. American Geophysical Union, San Fransisco, CA.
  • Type: Conference Papers and Presentations Status: Accepted Year Published: 2015 Citation: Johns A., Jastrow J.D.,Morris G., Six J., de Graaff M-A (2015)The impact of switchgrass cultivar diversity on nitrogen use efficiency. American Geophysical Union, San Fransisco, CA.


Progress 09/01/13 to 08/31/14

Outputs
Target Audience:Our products in this reporting period, which included presentations at interantional conferences, work groups, and seminars, as well as three publications, reached the international scientific community. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?We have hired a graduate student (Aislinn Johns) to work on this project. In addition, eight undergraduate students have contributed to this project in 2013 and 2014: (1) Jaron Adkins, (2) Mary Finnell. (3) Trevor Thornton, (4) Michael Brucker, (5) Dan Melody, (6) Kaisha Young, (7) Kimberly Tate, (8) Ariane Shannon. Jaron and Mary have presented a poster at the undergraduate research conference at Boise State University on their work, in addition, Jaron Adkins has presented his work at the AGU meetings in San Fransisco in 2013 and Aislinn Johns will present a poster at the AGU in 2015. How have the results been disseminated to communities of interest?We have presented results from this project at the AGU annual meeting in San Fransisco (2013), at the ESA annual meeting in Sacramento (2014), at a DOE workshop (Improved Representation of Roots in Models) at Oak Ridge National Laboratory (2014), at the SOM6 meeting in South Carolina (2014); at the ESA meeting in Baltimore in 2015, and at the CZO-workshop in Lafayette IL in October 2015. We have also presented our results at the AAIC conference in Washington DC (October, 2013), and at the NIFA-PD meeting in 2014. Presentations at international meetings: de Graaff M-A (2015) Root controls on soil organic carbon dynamics. Conference and workshop: Critical zone science, sustainability and services in a changing world: organic matter flux and stabilization in the critical zone. Lafayette, IN. de Graaff M-A, Jastrow J, Six J, Wullschleger S (2015) Fine root morphology as a driver of root and soil organic carbon decay rate. Ecological Society of America Annual Meeting, Baltimore, MD. Invited. de Graaff M-A (2014) Root controls on soil organic carbon stabilization and destabilization. SOM6 meeting, Kiawah Island, South Carolina. de Graaff M-A (2014) Root controls on soil organic carbon dynamics. Ecological Society of America Annual Meeting, Sacramento, California. Invited. de Graaff M-A (2014) Root controls on decomposition processes. Expert workshop: Improved Representation of Roots in Models. Oak Ridge National Laboratory, Tennessee. Invited. de Graaff M-A, Morris G, Jastrow J, Six J (2013) The impact of cultivar diversity in bioenergy feedstocks on soil carbon sequestration. AGU Annual Meeting, San Fransisco, California. de Graaff M-A, Morris G, Jastrow J, Six J (2013) At the root of sustainable bioenergy production: using genetic variation in root traits to maximize soil carbon restoration and biomass yields. AAIC 25th Annual Meeting "New Crops: Bioenergy, Biomaterials, and Sustainability" Washington D.C., 2013. Invited seminars Linking plant-soil relations to ecosystem processes in a changing climate. University of New Hampshire - Durham, NH. (2014) Articles: Refereed Publications *Denotes graduate student author; ** Denotes undergraduate student author Morris GP, Hu Z, Grabowski PP, Borevitz JO, de Graaff M-A, Miller RM, Jastrow JD (2015) Genotypic diversity effects on biomass production in native perennial bioenergy cropping systems. Global Change Biology Bioenergy (in press). Adkins J**., Jastrow JD, Morris G, Six J, de Graaff M-A (2015) Effects of switchgrass cultivars and intraspecific differences in root morphology on soil carbon stabilization. Geoderma (in press) de Graaff M-A, Adkins J**., Kardol P, Throop HL (2015) A meta-analysis of soil biodiversity impacts on the carbon cycle. Soil 1, 257-271. What do you plan to do during the next reporting period to accomplish the goals?We have accomplished all goals we set out to accomplish in year one, two and three, and have received a one-year extension to finish writing up two more manuscripts of which the data have been analyzed. We have started on conducting the life cycle analysis, which we will finalize by the summer of 2016.

Impacts
What was accomplished under these goals? Goal: To determine if shifting C3-dominated nonnative perennial old-field grasslands to C4-dominated native perennial grasslands directly repay the carbon (C) debt of land-use change by increasing soil C sequestration within the early years of establishment. Accomplishment: Upon comparing total soil C contents across all of our treatments, we have generated the following main results: (1) converting C3-dominated nonnative perennial old-field grasslands to C4- dominated native perennial grasslands results in a significant soil C debt in the first year after land-use change, (2) this debt is not paid back within the first five years following land-use change, regardless of plant species or plant species richness, however after four years of growth we found that Big Bluestem tends to accrue soil C at a faster rate than Switchgrass; (3) nitrogen fertilizer application (67 kg N/ ha) did not affect soil C sequestration rates four years following land use change. Goal: To determine if increases in root production and stabilization of root derived C in soil upon planting native perennials offset the losses in soil C from old fields. Accomplishment: We compared root-derived soil C contents along a gradient of increasing intra-specific diversity of native switchgrass perennials, and found that root-derived C accumulates in soils with big bluestem at a greater rate than in soils with switchgrass. We further found that root-derived C in switchgrass soils (0-15 cm) was positively related with SRL, but not with root biomass. These data indicate that differences in SRL among cultivars can differentially impact root C input and stabilization, and may be an important root trait to consider when optimizing soil C sequestration in bioenergy cropping systems. Goal: To assess whether increased variation in root traits in species and cultivar mixes of native perennial grasses will enhance biomass production and soil C storage. Outputs: A comparison of total soil C contents along a gradient of increasing inter- and intra-specific diversity of native perennials. Accomplishment: We compared total soil C contents in soils of old-fields and in soils converted from old-fields to C4-dominated native perennials. We found that (1) Increased species or cultivar diversity does not increase the rate of soil C sequestration in our experiment; (2) soils planted with monocultures, or with poly-cultures of Big bluestem cultivars accrue C at a greater rate than soils planted with switchgrass or any other species mix. A comparison of root-derived C stabilization in a variety of soil fractions defined by their ability to physically protect soil C along a gradient of increasing inter- and intra-specific diversity of native perennials. Accomplishments: Since increasing switchgrass diversity enhanced biomass production in switchgrass, but not big bluestem, we focused on quantifying how increasing diversity in switchgrass cultivars would impact root-derived soil C input and storage. Using density fractionations, we found that there are significant differences among cultivars in root derived soil C. Although we found no differences in total soil C upon a change in cultivar diversity, there were significant differences in the amount of plant derived C present in the switchgrass diversity plots. In the CPOM fractions, plots planted with 4 switchgrass cultivars had significantly more plant derived C than plots planted with 6 switchgrass cultivars (p = 0.013). In the silt fractions, 2-cultivar plots had more plant derived C than 6-cultivar plots (0.037), and in the clay fractions, 1-cultivar plots had more plant derived C than 2-cultivar plots (p = 0.002). Although there are differences in root derived C in different fractions among diversity levels, we cannot find any consistent patterns that allow us to conclude that increased diversity in switchgrass increases the stabilization of root derived C. A comparison of biomass production along a gradient of increasing inter- and intra-specific diversity of native perennials. Accomplishments: We have collected and analyzed plant biomass on a yearly basis and found that genotypic mixtures had one-third higher biomass production than the average monoculture, and no monoculture was significantly higher yielding than the average mixture.Further, year-to-year variation in yields was reduced in the mixture of switchgrass relative to the species monocultures. However, the effects of genotypic diversity on biomass composition were modest relative to the differences among genotypes. In conclusion (summary of goal 3): Since big bluestem accrued soil C at a much faster rate than switchgrass or any other species mix, our data indicate that species impacts trump cultivar and diversity impacts on soil C sequestration. However, soil C accrues slowly, and given that we found increased yield with increased diversity across all years of the experiment, diversity may positively impact soil C accrual in the future. In addition, since diversity stabilized yields between years, our data show that local genotypes can be included in biomass cropping systems without compromising yields and that genotypic mixtures could help provide high, stable yields of high-quality biomass feedstocks. Goal: To assess whether increased variation in root traits of cultivar mixes of native perennial grasses will increase the efficiency of nitrogen (N) cycling (i.e., decrease N losses). Accomplishments: We applied the 15N tracer to 64 of the switchgrass diversity plots in the spring of 2013. In 2014, we have harvested all the plant material from the subplots to which 15N was applied, and have analyzed this plant material for 15N content. We also subjected the roots to genotyping to ascertain that plots with greater plant diversity are diverse belowground. We found significant differences in standing biomass, nitrous oxide emissions and nitrogen use efficiency (NUE) among switchgrass cultivars, but found no evidence that increasing switchgrass cultivar diversity enhanced NUE, or any other N cycling processes. Further, we were unable to link the root structure as defined by SRL of the individual cultivars to NUE.

Publications

  • Type: Journal Articles Status: Published Year Published: 2015 Citation: de Graaff M-A, Adkins J., Kardol P, Throop HL (2015) A meta-analysis of soil biodiversity impacts on the carbon cycle. Soil 1, 257-271.
  • Type: Journal Articles Status: Accepted Year Published: 2015 Citation: Adkins J., Jastrow JD, Morris G, Six J, de Graaff M-A (2015) Effects of switchgrass cultivars and intraspecific differences in root morphology on soil carbon stabilization. Geoderma
  • Type: Journal Articles Status: Accepted Year Published: 2015 Citation: Morris GP, Hu Z, Grabowski PP, Borevitz JO, de Graaff M-A, Miller RM, Jastrow JD (2015) Genotypic diversity effects on biomass production in native perennial bioenergy cropping systems. Global Change Biology Bioenergy


Progress 09/01/12 to 08/31/13

Outputs
Target Audience: We have reached scientists and community members (Boise, ID) by giving presentations at international professional conferences and at local University-sponsored events. Specifically, we have presented three posters at one international (AGU) and two local (Boise State University) conferences. We have also presented our results at the AAIC conference in Washington DC (October, 2013). Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? We have hired one research technician (Shay Gillette) on the project. We have hired one graduate student (Mike Anderson) to work on the project. Mike will assess impacts of cultivar diversity on nutrient cycling. We have hired one undergraduate student (Jaron Adkins) to work on the project for. This student along with another undergraduate student (Aislinn Johns) has additionally acquired a grant from Boise State University to conduct a spin-off experiment that assesses how root architecture affects soil C sequestration through root-architecture induced differences in root-derived C stabilization. In addition, Jaron has presented his work on root-derived C stabilization in switchgrass cultivars at the AGU-international meetings in San Fransisco (2012). Two additional undergraduate students (Mary Finnell and Ariane Shannon) have volunteered their time in the lab to work on this project. One of these students has presented a poster on her work at the undergraduate research conference at Boise State University (summer, 2013). How have the results been disseminated to communities of interest? We have presented three posters at one international (AGU) and two local (Boise State University) conferences. We have also presented our results at the AAIC conference in Washington DC (October, 2013). What do you plan to do during the next reporting period to accomplish the goals? We have accomplished all goals we set out to accomplish in year one. We have started on soil fractionations to assess root-derived C stabilization across a switchgrass cultivar diversity gradient. The next harvest will take place in November, during this time, we will assess yield across all treatments in the agronomic and diversity trials and we will sample the plots that received the 15N tracer. These samples will be shipped to Boise State University, where they will be processed to assess cultivar diversity impacts on nutrient cycling.

Impacts
What was accomplished under these goals? We have accomplished the following goals of the project, all of which we set-out to accomplish during year 1. To determine if shifting C3-dominated nonnative perennial old-field grasslands to C4-dominated native perennial grasslands directly repay the C debt of land-use change by increasing soil C sequestration within the early years of establishment. We compared total soil C contents in soils of old-fields and in soils converted from old-fields to C4-dominated native perennials. Samples were collected off and on the crown of plants to depths of 0-5 cm and 5-15 cm from both the ‘agronomic trial’ and the ‘biodiversity trial’ at the sustainable bioenergy crop production research facility. We compared soil C in soils collected from 2012 and 2008, i.e. 4 years and 1 year since land-use change for cellulosic biofuel production with soils collected from previous land-use (i.e. C3-dominated nonnative perennial old-field grasslands). We have generated the following main results: (1) converting C3-dominated nonnative perennial old-field grasslands to C4-dominated native perennial grasslands results in a significant soil C debt in the first year after land-use change, (2) this debt is not paid back within the first four years following land-use change, regardless of plant species or plant species richness; (3) nitrogen fertilizer application (67 kg N/ ha) did not affect soil C sequestration rates. To assess whether increased variation in root traits in species and cultivar mixes of native perennial grasses will enhance biomass production and soil C storage. We compared total soil C contents along a gradient of increasing intra-specific diversity of native perennials. Samples were collected off and on the crown of plants to depths of 0-5 cm and 5-15 cm from the ‘biodiversity trial’ at the sustainable bioenergy crop production research facility. We compared soil C in soils collected from 2012 and 2008, i.e. 4 years and 1 year since land-use change for cellulosic biofuel production with soils collected from previous land-use (i.e. C3-dominated nonnative perennial old-field grasslands). We have generated the following main results: (1) Increasing intra-specific diversity enhanced biomass yields, although this effect was not transgressive, (2) increasing intra-specific diversity enhanced soil C storage to a depth of 0-5 cm in switchgrass, but not big bluestem plant species, and (3) soil C accumulates in big bluestem at a greater rate than in switchgrass. To assess whether increased variation in root traits of cultivar mixes of native perennial grasses will increase the efficiency of N cycling (i.e., decrease N losses). Outputs: Initiation of 15N tracer experiment in year 1 and a comparison of nitrogen use efficiency and N2O emissions along a gradient of increasing switchgrass diversity, which will be conducted in years 2 and 3. We have applied the 15N tracer to 64 of the switchgrass diversity plots in the spring of 2013.

Publications