Location: Rangeland Resources Research
2007 Annual Report
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:.
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.
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.