2008 Annual Report
3)of the NP 204 Action Plan, Problem Statements 3 (Grazinglands) and 4 (Pests). 3. Effects of elevated CO2 on nitrogen cycling in shortgrass steppe: Elevated CO2 has the potential to enhance plant growth and biomass accumulation, but these processes may be constrained by soil nitrogen availability. It is still uncertain how elevated CO2 affects long-term soil nitrogen dynamics. We examined the effect of five years of elevated CO2 on N dynamics in a native shortgrass steppe in northern Colorado using large open-top CO2-fumigation chambers. Plant growth and plant nitrogen uptake remained significantly higher under elevated than under ambient CO2 after five years of study. The indirect effect of elevated CO2 on soil moisture most likely increased nitrogen mineralization in the soil. These results suggest that plant responses to elevated CO2 are less constrained by nitrogen availability in semi-arid grasslands and could be more pronounced and last longer than in ecosystems that receive more moisture. This research addresses the Agricultural Ecosystem Impacts (Component.
3)of the NP 204 Action Plan, Problem Statement 3 (Grazinglands). 4. Grazing and drought impacts on soil carbon and microbial communities in northern mixed-grass prairie. The northern mixed-grass prairie represents the largest remaining intact rangeland in the US. Previous work in this rangeland ecosystem showed that heavy stocking rates increased soil carbon storage compared to light stocking or no grazing over a relatively wet period of years (1982-1992). Subsequent sampling following a dry period of years (1993-2002), including 5 drought years, determined the soil organic carbon in the light stocking and no grazing treatments were largely unaffected, whereas 30% of the soil organic carbon was lost in the heavy grazing treatment. In addition, soil microbial community structure differed with grazing treatments. The heavy stocking rate altered the plant community composition, which has reduced the aboveground productivity potential and subsequently modified the soil microbial community structure and associated biogeochemical (carbon and nitrogen) cycles. This research addresses Carbon Cycle and Carbon Storage (Component.
1)of the NP 204 Action Plan, Problem Statement 3 (Grazinglands, CRP and Buffers) 5. Ecological and Management Implications of Climate Change for American Rangelands: While most now accept that climate change is a reality, and many consider it the defining present-day environmental challenge, others wonder what it can possibly mean to them and what can done to prepare for it. In a special feature edition of Rangelands and also in the U.S. Climate Change Program’s Special Report, “The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity”, we synthesized the current climate change literature and reported on the potential effects of climate change on American rangelands, and presented management options for the ranchers and land managers who will have to deal with this problem. Among the more important rangeland responses to climate change identified were changes in plant species composition, including weed invasions, reductions in forage quality, and in some regions, increased drought and animal stress. Adaptive management strategies for coping with climate change included increased rangeland monitoring, development and use of models for predicting rangeland responses to climate change, better weather forecasting, and changing management objectives. This research addresses the Agricultural Ecosystem Impacts (Component.
3)of the NP 204 Action Plan, Problem Statements 3 (Grazinglands) and 4 (Pests). 6. Realistic Systems for Simulating Global Warming in Terrestrial Ecosystems: Performing experiments in which climate can be manipulated in a realistic field environment is a difficult yet necessary task if we are to understand how terrestrial ecosystems will respond to climate change. This project, led by an ARS collaborator from the US Arid Land Agricultural Research Center, developed infra-red heating array systems to be used in field environments to impose controlled heating for experiments to evaluate the consequences of warming on ecosystem functioning. The heating arrays were deployed over native grasslands at Haibei, Qinghai, China and at Cheyenne, Wyoming, and their efficiency and performance evaluated. The heating systems performed well, achieving target heating temperatures within 0.5°C 75% of their operation time, and with a heating efficiency which surpasses previous field warming systems. The infra-red hearing arrays are a useful method by which scientists can explore the consequences of global warming on crops and native agro-ecosystems, and are beginning to be adopted by other research groups around the world. This research addresses the Agricultural Ecosystem Impacts (Component.
3)of the NP 204 Action Plan, Problem Statements 2 (Cropping Systems) and 3 (Grazinglands). 7. Belowground nematodes resistant to rising atmospheric CO2. Soil organisms can have a profound affect on how changes in the environment, including climate change, affect the ecology of terrestrial ecosystems; they can be important in stimulating nutrient cycling and promoting plant growth, but may also be destructive to plants. In a report of three separate experiments, all conducted in grasslands and in which ambient levels of carbon dioxide(CO2) were increased to simulate CO2 concentrations projected for Earth’s atmosphere in the second half of this century, little evidence was found to suggest nematodes (various threadworms of the Phylum Nematoda) were affected by atmospheric CO2 concentration. These neutral responses to CO2 enrichment occurred despite increased root production in all three experiments, suggesting a simultaneous antagonistic mechanism may have operated, possibly decreased root quality and/or changes in the soil environment. The findings suggest that herbivorous nematodes in grassland ecosystems may sometimes be unresponsive to rising atmospheric CO2. This research addresses the Agricultural Ecosystem Impacts (Component.
3)of the NP 204 Action Plan, Problem Statement 3 (Grazinglands).
Morgan, J.A., Milchunas, D.G., Lecain, D.R., West, M.S., Mosier, A. 2007. Carbon dioxide enrichment alters plant community structure and accelerates promotes shrub growth in the shortgrass steppe. Proceedings of the National Academy of Sciences 104(37):14724-14729.
Morgan, J.A., Derner, J.D., Milchunas, D., Pendall, E. 2008. Management implications of global change for Great Plains rangelands. Rangelands 30(3):18-22.
Norton, U., Mosier, A., Morgan, J.A., Derner, J.D., Ingram, L.J., Stahl, P. 2008. Moisture pulses, trace gas emissions and soil C and N in cheatgrass and native grass-dominated sagebrush-steppe in Wyoming, USA. Soil Biology and Biochemistry 40:1421-1431.
Kandeler, E., Mosier, A., Morgan, J.A., Milchunas, D., King, J., Rudolph, S., Tscherko, D. 2007. Transient elevation of carbon dioxide modifies the microbial community composition in a semi-arid grassland. Soil Biology and Biochemistry 40:162-171.
Blumenthal, D.M., Chimner, R.A., Welker, J.M., Morgan, J.A. 2008. Increased snow facilitates plant invasion in mixed grass prairie. New Phytologist 179:440-448.
Ayers, E., Wall, D.H., Simmons, B.L., Field, C.B., Milchunas, D., Morgan, J.A., Roy, J. 2008. Belowground grassland herbivores are resistant to elevated atmospheric CO2 concentrations in grassland ecosystems. Soil Biology and Biochemistry 40:978-985.
Dijkstra, F.A., Pendall, E., Mosier, A., King, J., Milchunas, D., Morgan, J.A. 2008. Long-term enhancement of N availability and plant growth under elevated CO2 in a semiarid grassland. Functional Ecology 22:975-982.
Ingram, L.J., Stahl, P.D., Schuman, G.E., Buyer, J.S., Vance, G.F., Ganjegunte, G.K., Welker, J.W., Derner, J.D. 2008. Grazing and drought impacts on soil carbon and microbial communities in a mixed-grass ecosystem. Soil Science Society of America Journal 72(4):939-948.
Kimball, B.A., Conley, M.M., Wang, S., Xingwu, L., Morgan, J.A., Smith, D.P. 2008. Infrared heater arrays for warming ecosystem field plots. Global Change Biology, (14):309-320.