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 early March 2012 we harvested, baled, and weighed all Long Term Biomass Experiment (LTBE) plots to estimate 2011 net primary productivity. 2. Spring herbicide applications were made to control a flush of early spring weeds caused by an unusually warm and wet winter. Applications were conducted with a tractor-mount sprayer purchased with project funds. Sprayer size was chosen to meet specific size requirements of the LTBE plots. 3. Established a weather station on the LTBE site to record meteorological conditions and to provide data to calculate potential evapotranspiration. The datalogger in the station will support future addition of additional sensors, including a wireless soil moisture sensor network. 4. Completed soil texture analyses from the 2010 baseline soil cores. These data will be combined with data from soil electrical conductivity (EC) surveys, soil bulk density and soil carbon pool fractions, and carbon/nitrogen contents to develop spatial maps of soil properties. The texture work was 75% completed by a summer hire funded from the grant. 5. Completed early summer surveys of plant species composition in the LTBE native prairie plots. Late summer (peak biomass) surveys will be conducted in late August 2012. 6. Visited Texas AgriLife Research collaborator, Overton, TX, to see their switchgrass field plots, discuss approaches to establishing switchgrass/legume mixtures as a third treatment in LTBE, and discuss possible future collaboration. Switchgrass/legume mixtures are being considered to replace the existing Bermuda grass plots, which have failed to adequately establish because of the 2011 drought. 7. Designed an irrigation system to support precipitation manipulation experiments in subplots within the LTBE plots. Currently seeking sources of supplemental funds to augment grant funds to implement this system. 8. Established a cooperative agreement with Department of Integrative Biology collaborator, University of Texas at Austin, to fund a postdoc position to conduct research in the LTBE experiment. 9. Successfully recruited and filled the University of Texas-Austin postdoc position beginning on 16 May 2012.