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1a.Objectives (from AD-416):
The semi-arid grasslands of the western Great Plains, mixed-grass prairie and shortgrass steppe, provide a tremendous array of ecosystem services, including livestock forage, a diversity of native plants and animals, resistance to biological invasion, and carbon storage. Global change is expected to dramatically change grasslands and associated ecosystem services, but the nature of its impacts, and the mechanisms underlying those impacts, remain difficult to predict. In water-limited ecosystems, elevated CO2 and warming can have particularly strong and complex effects because, in addition to their direct effects, they alter water availability. Two main objectives will drive our research program over the next five years to understand how these changes might impact the ecosystem services of western rangelands. The first objective is to assess effects of predicted global changes on ecosystem services in a northern mixed-grass prairie. This will be accomplished by determining the effects of temperature, CO2 and precipitation on plant productivity, plant diversity, forage quality, community composition, weed invasion and the ability of native plant communities to recover from disturbance. The biogeochemistry underlying these responses will be studied to improve our understanding of ecosystem responses and to improve algorithms in biogeochemical models like Daycent. We will also evaluate whether and how responses of invasive species differ from those of native species. Our second objective is to develop knowledge and tools that allow rangeland managers to minimize greenhouse gas emissions. We will determine how temperature, CO2 and precipitation influence land-atmosphere exchanges of trace gases and soil carbon (C) storage, and evaluate the relative importance of water, nitrogen (N) and C limitation in regulating C storage. We will use this information plus additional soil C and CO2 flux data from long-term grazing experiments to determine the potential to mitigate greenhouse gas emissions through grazing management, and assess tradeoffs between mitigation and rangeland productivity. Objective 3. Develop science-based, region-specific information and technologies for agricultural and natural resource managers that enable climate-smart decision-making and where possible provide assistance to enable land managers to implement those decisions. The work will be conducted as the Northern Plains USDA Climate Change Hub and will be coordinated with NRCS, FS, and other USDA and non-USDA organizations in accordance with guidance found in the USDA Climate Change Hubs Charter, and Terms of Reference.

1b.Approach (from AD-416):
To address our first objective concerning the responses of rangelands to global changes, we will use a well-replicated Free Air CO2 Enrichment (FACE) and warming experiment to determine how global change influences the northern mixed-grass prairie. We will examine responses of plant production and quality, composition of native plant communities, carbon and nitrogen cycling, and plant invasion. To understand the mechanisms underlying these responses, we will make extensive use of gas exchange, stable isotope, soil water and nitrogen monitoring, and computer simulation methods. We will use additional treatments to learn how seasonality of precipitation influences the northern mixed-grass prairie, and how the magnitude of those effects compares to effects of CO2 and warming. To address our second objective concerning greenhouse gas mitigation tools, we will measure soil respiration and fluxes of nitrous oxide (N2O) and methane (CH4) using static chambers, and net ecosystem CO2 exchange (NEE) using dynamic chambers within plots of the FACE, warming and irrigation manipulative experiment. Results from the static and dynamic chambers will allow us to quantify CO2-enrichment and warming effects on soil trace gas fluxes and ecosystem level CO2 fluxes, and how these fluxes are related to soil moisture and other environmental factors. We will also take advantage of three ongoing NP215 long-term grazing studies to assess the effects of grazing management strategies (stocking rate and season of use) on the size and dynamics of soil C and N pools, and the potential of these strategies to mitigate greenhouse gas emissions in NMP and SGS. We will use natural variation in precipitation to determine the relative influence of above- and below-average years of precipitation on C and N pool changes. The insights provided by these experiments will help scientists and land managers adapt management practices to sustain ecosystem services in the face of global change, and provide critical information for policy makers. Utilize collaborative efforts within USDA (ARS, FS, NRCS, RMA, FSA and ERS) as well with other governmental entities (NOAA, USGS, BLM, NWS), land grant university agricultural experiment stations and agricultural extension (in Northern Plains regional states of WY, CO, MT, ND, SD and NE) to synthesize information and data and knowledge to develop technologies (management strategies, management practices) and decision support tools (applications for mobile devices, enhanced models) that can be delivered to land managers via web portals and other technology transfer providers (extension, education, NRCS field offices, eXtension, etc.). An outreach coordinator is needed to manage the 6 state efforts.

3.Progress Report:
Research under project 5409-110-005-00D is guided by two objectives: (1) Assess effects of predicted global changes on ecosystem services in northern mixed-grass prairie, and (2) Develop knowledge and tools that allow rangeland managers to minimize greenhouse gas emissions. Both objectives are centered on the Prairie Heating and CO2 Enrichment (PHACE) Experiment in which atmospheric carbon dioxide (CO2) concentration, temperature and soil water are all being manipulated to further our understanding of how semi-arid rangelands respond to multiple global change factors. The second objective includes measurements of soil carbon within a separate, long-term grazing experiment. A core group of scientists from ARS, the University of Wyoming, Colorado State University, The University of Western Sydney, Australia, and the Biometeorology Institute in Florence, Italy, plus several graduate students and post docs continue to collaborate on this unique project. A post-doc hired in 2013 to replace one of the two lead scientists who retired continues to be central to work on the PHACE experiment. The experimental plots are divided into two halves, with one side comprised of a native northern mixed-grass prairie, and the other side seeded under different disturbance regimes with various native and invasive plant species. This plot arrangement allows us to evaluate both the basic responses of this rangeland to climate change, and also to investigate how global changes interact with disturbance and plant invasion. Our results to date suggest that the effects of elevated CO2 and warmer temperatures depend to a large extent on the combined effects of these two factors on soil plant water relations. Due to higher-than-expected water savings from elevated CO2, productivity in this semi-arid rangeland may be greater under climate warming than previously suspected. Furthermore, growing seasons may be lengthened not only by warming, as expected, but also by elevated CO2, which can delay drought-induced senescence. However, we are also learning how a number of other plant and soil attributes, particularly the cycling of soil/plant nitrogen (N) may determine the ultimate responses of this rangeland to climate change through competition for soil resources. Experimental work on Dalmatian toadflax (Linaria dalmatica, a perennial invasive perennial forb) demonstrated that elevated CO2 and warming led to a 13-fold increase in its invasion of mixed-grass prairie. Similar results have now been observed for other invasive species, including diffuse knapweed (Centaurea diffusa) and cheatgrass (Bromus tectorum). A Department of Energy grant extended the PHACE experiment through 2013 and includes adding additional modeling efforts using results from this experiment to evaluate longer term effects of climate change on carbon (C) cycling. Experimental treatments ended in July 2013, and the primary objective since then has been to process the large number of below-ground samples collected in 2013. Specific studies include effects of elevated CO2 and warming on.
1)root architecture and chemistry of key rangeland species;.
2)microbial carbon use efficiency and effects on nitrogen availability; rhizosphere N fixation; root crown biomass and chemistry; soil nematodes; and mycorrhizae. Three graduate students are contributing to this research. We also continue efforts to use leaf traits to predict global change responses, both within the PHACE experiment and through synthesis of literature from prior global change experiments. In our greenhouse gas mitigation research, we processed soils harvested in 2013 for soil C and N content, to determine the long-term effects of livestock grazing on soil C sequestration and storage. In 2014, we began collaborative efforts with the Bureau of Land Management to adapt grassland restoration practices to climate change. This project uses seeds collected by the BLM Seeds of Success program to test (1) how much global change responses vary among plant species and among populations within species and (2) whether global change responses can be predicted by the origin and/or water-use traits of species and populations. In 2014 we obtained seeds for 90 different populations originating from across a wide latitudinal gradient in the Rocky Mountain States. We then planted the experiment and imposed both elevated CO2 and warming treatments within growth chambers. Measurements will begin in July 2014, and continue into FY 15. Also in 2014, new funding associated with the USDA Climate Hubs was received and a 3rd objective added to this project: Develop science-based, region-specific information and technologies for agricultural and natural resource managers that enable climate-smart decision-making and where possible provide assistance to enable land managers to implement those decisions. The work will be conducted as the Northern Plains USDA Climate Change Hub and will be coordinated with Natural Resources Conservation Service (NRCS), Forest Service (FS), and other USDA and non-USDA organizations in accordance with guidance found in the USDA Climate Change Hubs Charter, and Terms of Reference. Efforts in 2014 centered on engagement with Extension programs in the six regional states (Montana, Wyoming, Colorado, North Dakota, South Dakota and Nebraska) regarding disseminating information to, and receiving feedback from, agricultural producers on tools and management practices for enhanced decision making with increased weather variability and extreme events (e.g., drought).

4.Accomplishments
1. Rising atmospheric carbon dioxide leads to longer growing seasons. While longer growing seasons around the world have been attributed to climate warming over the past century, new research by ARS scientists in Fort Collins, CO suggest another factor may be involved. A unique climate change experiment undertaken in native prairie at the High Plains Grassland Research Station near Cheyenne, WY revealed that artificially raising the ambient temperature of the prairie vegetation 3-5° F - levels expected by the end of this century - did increase the length of the growing season, but the response was more pronounced when accompanied by an increase in the ambient carbon dioxide concentration from the present-day level of 400 parts per million (ppm) to 600 ppm. Carbon dioxide is known to increase plant water use efficiency, and the group showed that lower consumptive plant water use in plots exposed to both artificial warming and carbon dioxide enrichment conserved soil moisture, allowing the plants to grow later into the fall. These results, which suggest that growing seasons in water-limited ecosystems may lengthen due to both warming and elevated CO2, will be critical in developing adaptive management and genetic strategies to climate change.

2. Herbivory counteracts nutrient pollution in grasslands across the globe. Grasslands not only provide forage for the majority of the world’s livestock but are also key repositories of biological diversity. Many grasslands are threatened, however, by nutrient pollution and consequent reductions in light availability. ARS scientists from Ft. Collins, CO, working with collaborators from the global Nutrient Network experiment, demonstrated that across 40 grasslands from around the world, where herbivory increases light availability, it also mitigates effects of nutrient pollution on plant diversity. These results will help rangeland scientists and managers predict where grazing can be used to maintain diversity in the face of nitrogen deposition and other forms of nutrient pollution.

Review Publications
Ibanez, I., Diez, J., Miller, L.P., Olden, J.D., Sorte, C.J., Blumenthal, D.M., Bradley, B.A., D'Antonio, C.M., Dukes, J.S., Early, R.I. 2014. Integrated assessment of biological invasions. Ecological Applications. 24:25-37.