1a. Objectives (from AD-416)
Our research objective is to initiate a long-term field experiment to determine the temporal stability of ecosystem service provision from switchgrass monocultures, improved pastures, and low input/high diversity native grassland. Ecosystem services of primary interest are plant biomass production and soil carbon storage, and their responses to two major stressors: 1. Climate change (variability in water availability caused by changes in precipitation patterns) and 2. Invasive plant species (invasions by the introduced grass Sorghum halapense, Johnsongrass). The central hypothesis guiding this research is that net ecosystem service provision is greater from high diversity native grassland than monocultures. This result is expected because we predict that: 1. Temporal variability in plant biomass production due to varying climate is lower than monocultures, 2. Net bioenergy potential (biomass produced - inputs) and carbon storage is greater than monocultures, and 3. Susceptibility to invasive plant species is reduced.
1b. Approach (from AD-416)
Our approach focuses on a large-scale field study that will provide information for parameterizing a plant growth model (ALMANAC) and a coupled soil-plant-atmosphere biogeochemistry model (SPAB). Replicated 0.63 ha (1.5 ac) plots will be planted with three treatments: 1. Switchgrass (Panicum virgatum) in monoculture, 2. Coastal bermudagrass (Cynodon dactylon L.) in monoculture, and 3. Native prairie polyculture of 30 native prairie species, including common dominant C4 grasses and numerous forbs. Nitrogen fertilizer will be added to half the switchgrass and coastal bermudagrass plots and subplots within the native prairie plots (150 lb N ac-1). Subplots within each planting treatment will be irrigated to replace evapotranspiration to minimize water limitation of plant and soil processes by minimizing seasonal and interannual variability in water availability. Additional subplots will be planted with seeds of a widespread introduced invasive grass, Sorghum halapense (Johnsongrass), to test invasibility. Measurements of plant biomass and its bioenergy potential, plant community composition, plant and soil pools and fluxes of carbon and nitrogen, microclimate, and soil moisture will be conducted to quantify differences in ecosystem service provision among these treatments. Field data will be used to parameterize two models: 1. ALMANAC: This plant growth model will simulate plant biomass production and will be calibrated and verified for each planting treatment. Additional simulations will be run to predict production under environmental scenarios beyond those represented in the experiment. 2. SPAB: This coupled soil-plant-atmosphere biogeochemistry model will predict long-term probability distributions of soil carbon storage.
3. Progress Report
1. In spring 2011 we harvested, baled, and weighed the 2010 growth to estimate baseline productivity. This was accomplished with the help of a front-end loader weighing system installed on a John Deere tractor, purchased with grant funds, and now available for use by all researchers. 2. Plots planted to Switchgrass were overseeded with an upland variety (Blackwell) to aid plot establishment. 3. In fall 2010, collaborator conducted electrical conductivity (EC) surveys of all 24 plots, to help establish baseline soil conditions. The EC surveys were used to pick locations for soil coring that represented the full range of variability in soil properties. Soil cores were processed to determine bulk density and are being further processed to measure soil texture. Under a cooperative agreement with collaborator at Brigham Young University, carbon pool fractions and carbon and nitrogen contents are being determined. Soil texture determinations are being conducted by a summer hire funded from the grant. 4. Texas AgriLife collaborator has developed 1-m digital elevation maps of the site, and assisted with choosing the location for a weather station to be deployed in fall 2011. 5. The 2011 growing season is a planned establishment year in the experiment, and no sampling activities are being conducted. Planning is underway for purchase of the weather station and for installation of irrigation systems needed for experimental objectives. Progress was reported to the funding agency in a presentation to the NIFA program officer in Washington, D.C.