Beginning in FY07, CSiTE reorganized around seven scientific themes and coordinated research activities at field experiments in switchgrass ecosystems managed for biomass production at Milan, Tennessee, and the Fermilab site at Batavia, Illinois.The seven themes (Figure 1) are:
2) Soil structural controls
3) Microbial community function and dynamics,
4) Humification chemistry,
5) Intrasolum carbon transport,
6) Mechanistic modeling
7) Integrated evaluation
Figure 1. The seven research themes of CSiTE and their relationships to each other.
Each of the five experimental theme’s research contributes to the sixth theme, Mechanistic Modeling which allows us to explore the effects of different processes, carbon inputs, and environmental conditions on enhancing of carbon sequestration at a local scale. The seventh theme, Integrated Evaluation of Carbon Sequestration Technologies, draws upon the Mechanistic Modeling theme for estimates of potential soil C sequestration across the wide range of soils, climate, and crops and management regimes possible in the U.S. By combining those estimates with the greenhouse gas (GHG) emissions and the economic value of those crops and management regimes, the seventh theme explores the economic consequences and GHG benefits for various strategies to enhance soil C sequestration at the national scale.
For the five experimental themes we have selected:
located in western Tennessee
as our primary test soil type and a Mollisol located in northeastern
our secondary test soil type. As research evolves we will explore other
ecosystems managed for cellulosic biomass production as our testbed
We intend that poplar ecosystems be addressed in later years.
|• Manipulations of C input and soil conditions to affect C sequestration processes at the sites.|
We use the Erosion Productivity Impact Calculator (EPIC) (Izaurralde et al. 2006) as the basis of our mechanistic modeling activities. We use the systems modeling language STELLA® as a tool to engage the experimental scientists in building the conceptual and quantitative links among the five experimental themes in a way that can then be incorporated into the more multidimensional EPIC model and as a means for conducting model-based experiments for testing hypotheses about predicted effects of genotypic and environmental factors on soil C accrual.. The Forest and Agriculture Sector Optimizing Model (FASOM) model (McCarl and Schneider 2001), which is already integrated with EPIC and depicts total U.S. agricultural and forestry activities over time incorporating GHG issues of permanence, leakage, and additionality, forms the basis for our regional- to national-scale analysis of developed and potential soil C sequestration enhancement opportunities.
Research across all seven themes coalesces around the experimental switchgrass ecosystems managed for biomass production and is designed to address five overarching scientific questions:
is the nature of belowground C inputs
by switchgrass, and are they compatible with sustained aboveground
production and soil C sequestration?
What are the
fundamental physical, chemical,
and microbial mechanisms controlling C accrual and storage in soil, and
they interact in space and time?
III. What processes control the movement and distribution of C through the soil profile?
How are the fundamental
C distribution and movement manifested across landscapes and time?
fundamental knowledge best be used to
identify and implement methods and practices for sustained enhancement
C in the context of biomass production for energy in an environmentally
acceptable and economically feasible fashion?
for transforming experimentally derived understanding to forecasting
CSiTE seeks to ensure that its fundamental science findings are used to inform and improve carbon sequestration forecasting capabilities by taking a vertically integrated approach which links field experiments to conceptual models, and conceptual models to forecasting models and regional models. (Figure 2). In this manner CSiTE strives to contribute to the effective application of carbon sequestration technologies to mitigate CO2-induced climate change.
Click on a Theme to Expand. Click again to Close.
Participants – Julie Jastrow (ANL), Mike Miller (ANL), Roser Matamala (ANL), Cesar Izaurralde (PNNL), Carla Gunderson (ORNL), Robin Graham (ORNL), Rattan Lal (Ohio State University), Don Tyler ( University of Tennessee), Dave Parrish ( VA Polytechnical Institute)
The purpose of the soil C inputs theme is to quantify belowground C inputs and root dynamics within the framework of the four CSiTE experiments. The theme plan is designed to characterize treatment (i.e., cultivar and fertilization) differences and intra-annual variation in 1) root production, 2) root mortality and decomposition, and 3) root and microbial respiration at Milan, Fermilab, and possibly ORNL and to evaluate, on that basis, proposed strategies for enhancing soil C sequestration beneath switchgrass. In addition, the soil samples taken under the auspices of this theme will be used in the other four experimental themes. This theme is focused on addressing the timing, quality, quantity, and distribution with depth of belowground C inputs beneath switchgrass. Thus it directly addresses the first overarching science question: “What is the nature of belowground C inputs by switchgrass, and are they compatible with sustained aboveground biomass production and soil C sequestration simultaneously?“ Theme 1 also contributes to a better understanding of the distribution of C through the soil profile and thus also relates to the fourth overarching question: “How are the fundamental processes controlling soil C distribution and movement manifested across landscapes and time?”
belowground C inputs and the contribution of root production and
turnover to soil C dynamics in terrestrial ecosystems are some of the
grand ecological challenges of the 21st century. Currently, there is a
diverse set of direct and indirect methods for measuring plant root
production and mortality with no overall consensus on which method is
best suited for accurate estimation of root dynamics (Vogt et al.
1998). Despite a widespread lack of agreement on which methods are
best, there is universal agreement that belowground studies are
labor-intensive and often carry large uncertainties about estimates of
root production and mortality. Advantages and disadvantages of
different methods are widely recognized and are an important
consideration when selecting an overall approach to studies of plant
root dynamics (Vogt et al. 1998). Root biomass is more than two-thirds
of the total biomass in switchgrass plantations (Ma et al. 2001), and
studies of root dynamics as they determine soil C inputs are an
essential part of understanding soil C sequestration in these systems.
Depth profiles of coarse root biomass (>2 mm) for the Alamo switchgrass cultivar have been previously examined at Milan (Garten and Wullschleger 1999). Both coarse root biomass and soil organic C inventories decline in a semi-logarithmic manner with soil depth. Summation of measured and predicted amounts of biomass to a depth of 3 m at Milan indicates that >75% of the coarse root biomass resides in the top 40 cm of soil. This finding is similar to those of other investigations on the vertical distribution of switchgrass root biomass (Ma et al. 2000; Frank et al. 2004). Based on 13C natural abundance measurements, Garten and Wullschleger (2000) estimated an input of 210 g C m-2 y-1 beneath switchgrass at Milan. The former estimate was preliminary but represents approximately one-third of the C captured aboveground by annual switchgrass production. Preliminary estimates for the turnover time for C in coarse switchgrass roots were on the order of 1 to 2 years (Garten and Wullschleger 2000). Other investigations of root dynamics beneath switchgrass indicate that coarse roots are <20% of total root biomass (Tufekcioglu et al. 1999); therefore, much remains to be learned about the distribution and dynamics of switchgrass fine roots that undoubtedly will comprise most of the belowground biomass at Milan, Fermilab, and ORNL.
While the principal source of detritus and soil organic matter under switchgrass is the root system, the rate of soil C turnover may ultimately determine the potential for soil C sequestration. Soil respiration measurements integrate the biological activity of roots and microbes that determine soil C turnover rates. It is important to separate root from microbial respiration when assessing the effects of different treatments on soil C dynamics. For example, Parkin et al. (2005) reported differences in microbial respiration between landscape positions that were correlated with organic matter and microbial biomass content; however, the effect of landscape position was masked by differences in root respiration between crops. Environmental factors, particularly temperature and water availability because they influence plant activity and organic matter decomposition, are important in controlling soil respiration. In addition, substrate quality and soil nutrients influence the rates of C turnover. In a comparison with cool-season grasses, Tufekcioglu et al. (2001) found that switchgrass had the highest live, fine-root biomass and the lowest soil respiration. Another study indicated that differences in physiology (small root turnover or low specific root respiration) possibly lead to low rates of C turnover beneath switchgrass and contribute to greater soil C accumulation (Marquez et al. 1999). Finally, management practices are known to affect soil C turnover. Mulching and adding straw have been shown to have positive effects on soil C sequestration in croplands (Rees and Chow 2005), and Ma et al. (2000) showed that soil respiration and soil C turnover were greater when switchgrass was harvested once instead of twice in a sandy loam soil. However, while there is evidence that management practices can affect soil C turnover, the effects of management practices such as nutrient amendments on soil organic matter have not been extensively studied.
This research is driven by the following science questions: