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United States Department of Agriculture

Agricultural Research Service

Research Project: GLOBAL CHANGE: RESPONSES AND MANAGEMENT STRATEGIES FOR SEMI-ARID RANGELANDS

Location: Rangeland Resources Research

2007 Annual Report


1a.Objectives (from AD-416)
Objective I: Assess/project changes in the structure and functioning of Great Plains grasslands due to the interactive effects of elevated CO2 and legume N on primary production, N and C cycling, and plant community dynamics, including invasive weeds. Objective II: Develop management strategies that optimize responses of semi-arid rangeland to global change and minimize emission of greenhouse gases (GHGs).


1b.Approach (from AD-416)
We will use novel Free Air CO2 Enrichment (FACE) technology to expose the native northern mixed-grass prairie (NMP) to a gradient of CO2 concentrations from present ambient levels of approximately 370 to 670 parts per million. Within the CO2 gradient, plots consisting of native NMP and NMP inter-planted with combinations of legume and invasive weed species will evaluate how legume N interacts with CO2 to affect soil C and N cycling, trace gas fluxes, water relations, plant physiology/demography/phenology, reproductive and vegetative recruitment, weed invasion, and plant community dynamics. In a related modeling exercise, data from previous CO2 enrichment and flux experiments will be used to predict long-term weather and global change responses of Great Plains grasslands. A second objective will evaluate the impacts of management strategies on C and N cycling and land-atmosphere exchange of greenhouse gases. The responses of soil C and N dynamics to variable grazing intensity and seasonality will be determined. Inter-seeding legumes into rangeland will be evaluated for its potential to enhance biomass production, forage quality, and mitigate greenhouse gas emissions. This information will be used to develop new management practices that consider trace gas emissions, in addition to more traditional rangeland goods and services.


4.Accomplishments
Rising atmospheric CO2 alters the botanical structure of the Colorado Shortgrass Steppe: Rising atmospheric CO2 has been implicated in the encroachment of woody plants into many world grasslands over the past two centuries, a process which is contributing to their degradation. However, no direct evidence yet exists to support the involvement of CO2 in woody plant invasions. Research using large open-top CO2-fumigation chambers placed over native shortgrass steppe in northern Colorado showed that doubling CO2 over five years resulted in an approximately 84% increase in productivity of a perennial native grass, Stipa comata (needle-and-thread), and a 40-fold increase in aboveground biomass of Artemisia frigida (fringed sagewort), a common sub-shrub of some North American and Asian grasslands; none of the other 34 plant species responded to CO2. These results illustrate that rising atmospheric CO2 can affect species changes due to differential species sensitivities to CO2, and are the first evidence from a manipulative field experiment implicating rising atmospheric CO2 in rangeland woody plant invasions. Ecologists, land managers, and policy makers will need to consider this impact of rising atmospheric CO2 on rangeland plant community shifts in the formulation of management practices and greenhouse gas emissions policy. This research addresses the Agricultural Ecosystem Impacts of the NP 204 Action Plan, and specifically the effects of increasing carbon dioxide and other stressors on weeds and grazinglands.

Land management and precipitation effects on carbon sequestration in rangelands: Proper management of rangelands offers opportunities to partially mitigate the rise in atmospheric carbon dioxide concentrations through sequestration of this additional carbon via storage in biomass and soil organic matter, a process termed carbon sequestration. Findings from a synthesis of available literature involving carbon sequestration and rangelands in the North American Great Plains included:.
1)carbon sequestration decreases with increasing mean annual precipitation in native rangelands of the North American Great Plains,.
2)a general trend for grazing was a decrease in carbon sequestration with longevity of the grazing management practice, and.
3)carbon sequestration increased with time since interseeding of a nitrogen-fixing legume, illustrating the importance of nitrogen in carbon sequestration. The arena of management-environmental interactions is largely unexplored at this time, but knowledge developed here will increase understanding of nutrient cycling through climate-plant-soil-microbial interactions. These findings address the Carbon Cycle and Carbon Storage component of the NP204 Action Plan, and specifically the problem statement concerning the quantification of the magnitude and rate of change of soil carbon storage with different land use management practices, in different ecoregions, and under different plant communities.

Can selecting for CO2 responsiveness increase crop productivity?: Since crops have been bred under steadily increasing levels of atmospheric CO2, it is generally assumed that today’s crops are well suited to present-day high CO2 levels, and will adapt to future levels. This assumption, however, has never been tested. To test it, we grew oat (Avena sativa) cultivars that had been released early and late in the 20th century, in CO2 concentrations representative of the 1920s, current levels, and a projected future concentration for the middle of this century, (300, 400 and 500 parts per million, respectively). In contrast to our predictions, newer lines were less responsive than older lines to rising CO2 in terms of both leaf area and tiller number. New and old lines responded similarly to CO2 in terms of biomass, relative growth rate, and leaf area ratio. Newer lines were also less variable in their response to CO2 than were older lines, and the most responsive lines were found among the older cultivars. Our results suggest that for oat: (a) newer lines are not intrinsically more responsive to rising CO2 levels than older lines; and (b) phenotypic homogenization among modern lines could hamper efforts to identify desirable characteristics associated with CO2 responsiveness. This research addresses the Agricultural Ecosystem Impacts of the NP 204 Action Plan, and specifically the effects of increasing carbon dioxide and other stressors on cropping systems.

Dry conditions and the presence of an invasive annual grass enhance greenhouse gas emissions from semi-arid rangelands: With increased acceptance by the scientific community on the central role of greenhouse gas (GHG) emissions in global climate change, a key question remains concerning the potential of agriculture to mitigate the problem through practices which reduce GHG emissions. We have addressed this problem in semi-arid rangelands in experiments characterizing how weather and disturbance affect trace gas fluxes of semi-arid rangelands. In general, dry conditions in grasslands of the Northern Great Plains lead to small annual emissions of CO2, and wetter years lead to its assimilation. Further, the emission of GHG from Wyoming sagebrush steppe may increase with cheatgrass invasion due to fundamental changes in nutrient cycling. The results of this work suggest that weather and the presence of weeds need to be considered in determining the feasibility of management practices for enhancing carbon storage in rangelands. These findings address the Carbon Cycle and Carbon Storage component of the NP204 Action Plan, and specifically the problem statement concerning the quantification of the magnitude and rate of change of soil carbon storage with different land use management practices, in different ecoregions, and under different plant communities.

Soil biology feed-backs under elevated CO2. The responses of ecosystems to global change are determined in large part by a multitude of soil biological activities which collectively determine the availability of soil nutrients to plants, microorganisms and soil fauna. In a field experiment using large open-top CO2-fumigation chambers placed over native shortgrass steppe in northern Colorado, measurements of soil microbial biomass, enzyme activities and abundances of phospholipid fatty acids (PLFAs) illustrate how feed-backs in the soil microbial community can influence nutrient cycling, and ultimately, ecosystem responses to rising atmospheric CO2. While growth at elevated CO2 led to higher enzyme activities in the upper soil layers only, CO2 had no effect on microbial biomass. A shift towards a more fungal-dominated community in the third year of the experiment was in apparent response to declining forage quality of plants exposed to high CO2 concentrations, and should slow down C cycling, leading to greater C sequestration. This research provides critical information on how grassland C cycling will respond to rising concentrations of atmospheric CO2. These findings address the Carbon Cycle and Carbon Storage (quantification of the magnitude and rate of change of soil carbon storage) as well as the Agricultural Ecosystem Impacts (effects of CO2 and other stressors on rangelands) components of the NP204 Action Plan.

Rising atmospheric CO2 and warming are predicted to affect semi-arid grasslands through changes in water and nutrient cycles. A new field experiment, the Prairie Heating and CO2 Enrichment (PHACE) Experiment, was initiated this year to evaluate how combined warming and rising CO2 in Earth’s atmosphere will affect the ecology of semi-arid grasslands. A computer simulation of the five-year experiment using the DAYCENT ecosystem model indicated that year-to-year variability in soil water content and consequences for soil nutrient cycling will be most important in determining whether combined higher CO2 and warmer temperatures will stimulate or reduce plant production over the next five years (2007-2011). These results suggest that for water-limited systems like semi-arid rangelands, understanding how future precipitation patterns change in concert with rising CO2 and temperature and collectively impact soil water content may be critical in forecasting the impacts of global climate change on rangeland forage production. Comparing the modeling results with the actual outcomes of the experiment over the next five years will be helpful in understanding the capability of the DAYCENT model to predict future ecosystem responses to global change. This research addresses the Agricultural Ecosystem Impacts of the NP 204 Action Plan, and specifically the effects of increasing carbon dioxide and other stressors on rangelands.


6.Technology Transfer

Number of web sites managed1
Number of non-peer reviewed presentations and proceedings10
Number of newspaper articles and other presentations for non-science audiences14

Review Publications
Derner, J.D., Schuman, G.E. 2007. Carbon sequestration and rangelands: A synthesis of land management and precipitation effects. Journal of Soil and Water Conservation 62(2):77-85.

Morgan, J.A. 2001. Ecosystems and their goods and services, Chapter 5: Climate Change 2001. pp. 235-342. In: J.J. McCarthy, et.al. (eds). The Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), Cambridge University Press, Cambridge UK.

Morgan, J.A. 2005. Rising atmospheric CO2 and climate change: Management implications for grazing lands. pp. 245-272. In: S.G. Reynolds and J. Frame (eds) Grasslands: Developments Opportunities Perspectives. FAO and Science Pub., Inc.

Pendall, E.L., King, J.Y., Mosier, A.R., Morgan, J.A., Milchunas, D. 2005. Stable isotope constraints on net ecosystem production under elevated CO2. pp. 182-198. In: L.B. Flanagan, J.R. Ehleringer and D.E. Pataki (eds) Stable isotopes and biosphere-atmospheric interactions: Processes and biological controls. Book Chapter. Elsevier, Inc., San Diego, CA.

Potter, K.N., Derner, J.D. 2006. Soil carbon pools in Central Texas: prairies, restored grasslands, and croplands. Journal of Soil and Water Conservation. 61(3):124-128.

Korner, C., Morgan, J.A., Norby, R. 2007. CO2 fertilization: When, where, how much? pp 9-22. In: Canadell, J.G., Pataki, D.E., Pitelka, L.F. (eds), Terrestrial ecosystems in a changing world. The IGBP series. 336 pages. Springer, Berlin.

Parton, W.J., Morgan, J.A., Wang, G., Del Grosso, S.J. 2007. Projected Ecosystem Impact of the Prairie Heating and CO2 Enrichment Experiment. New Phytologist 174:823-834.

Mosier, A.R., Morgan, J.A., King, J.Y., Lecain, D.R., Milchunas, D.G. 2002. Soil-atmosphere exchange of CH4, CO2, NOx, and N2O in the Colorado shortgrass steppe under elevated CO2. Plant and Soil Journal 240:201-211.

Gill, R.A., Kelly, R.H., Parton, W.J., Day, K.A., Jackson, R.B., Morgan, J.A., Scurlock, J.M., Tieszen, L.L., Castle, J.V. 2002. Using simple environmental variables to estimate belowground productivity in grasslands. Global Ecology and Biogeographical Letters 11(1):79-86.

Wylie, B.K., Fosnight, E.A., Gilmanov, T.G., Frank, A.B., Morgan, J.A., Haferkamp, M.R., Myers, T.P. 2007. Adaptive data-driven models for estimating carbon fluxes in the northern great plains. Remote Sensing of Environment 106:399-413.

Last Modified: 7/30/2014
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