Grassland Ecosystem Function Projects
NutNet (Nutrient Network)
We are participating in a large, collaborative nutrient addition project called the Nutrient Network (NutNet) organized by Drs. Elizabeth Borer and Eric Seabloom. The purpose of this international project is to assess the general factors that drive community processes in herbaceous-dominated ecosystems. Nutrient additions (N, P, and K) and grazing exclosures were implemented beginning in 2008 in order to assess top-down (consumer) vs. bottom-up (nutrient) controls in these systems. We have set up two sites in Kentucky that contribute data to this endeavor: one in a managed pasture (dominated by cool-season, non-native species) located here in Lexington, and a second in at Hall’s Prairie, a restored native warm-season grassland in western KY. We monitor tall fescue endophyte infection frequencies at the mananged grassland site, and levels of seed predation by rodents at both sites in addition to the full suite of NutNet measurements (biomass, species composition, light availability, etc.). Jim Nelson is the primary contact for this project.
Recent Manuscripts
Anderson, T.M., D. Griffith, J. Grace, E. Lind, P. Adler, L. Biederman, D. Blumenthal, P. Daleo, J. Firn, N. Hagenah, A. MacDougall, R. McCulley, S. Prober, A. Risch, M. Sankaran, M. Schutz, E. Seabloom, C. Stevens, L. Sullivan, P. Wragg, and E. Borer. 2018. Herbivory and eutrophication mediate grassland plant nutrient responses across a global climatic gradient. Ecology
Biederman, L.A., B. Mortensen, P.A. Fay, N. Hagenah, J. Knops, K. La Pierre, R. Laungani, E. Lind, R.L. McCulley, S. Power, E.W. Seabloom, P. Tognetti. 2017. Nutrient addition shifts plant community composition towards earlier flowering species in some prairie ecoregions in the U.S. Central Plains. PLOS ONE. https://doi.org/10.1371/journal.pone.0178440
Hautier, Y., I. Forest, E.T. Borer, E.W. Seabloom, W.S. Harpole, E.M. Lind, A.S. MacDougall, C.J. Stevens, P.B. Adler, J. Alberti, J.D. Bakker, L.A. Brudvig, Y.M. Buckley, M. Cadotte, M.C. Caldeira, E.J. Chaneton, C. Chu, P. Daleo, C.R. Dickman, J.M. Dwyer, A. Eskelinen, P.A. Fay, J. Firn, N. Hagenah, H. Hillebrand, O. Iribarne, K.P. Kirkham, J.M.H. Knops, K.J. La Pierre, R.L. McCulley, J.W. Morgan, M. Partel, J. Pascual, J.N. Price, S.M. Prober, A.C. Risch, M. Sankaran, M. Schuetz, R.J. Standish, R. Virtanen, G.M. Wardle, L. Yahdjian, and A. Hector. 2017. Local loss and spatial homogenization of plant diversity reduce ecosystem multifunctionality. Nature Ecology & Evolution https://doi.org/10.1038/s41559-017-0395-0
Please contact Rebecca for copies.
Decomposition in Drylands: Soil Erosion and UV Interactions
This collaborative project seeks to understand the fundamental drivers of decomposition in arid grasslands. Recent independent studies have suggested that both UV and soil erosion/deposition play critical roles in this important ecosystem process, potentially in contrasting ways. This project tests the hypothesis that radiant energy (UV) and soil movement drivers interact, such that UV effects on litter decomposition predominate up to a certain level of soil deposition and are then negated. Therefore, shifts in grass-woody plant abundance in drylands affect decomposition rates by mediating soil transport processes that determine the extent of litter-soil contact; and that enhancement of microbial activity by soil accumulation more than offsets associated reductions in UV photodegradation. We provide part of the microbial component of this project. We have developed phospholipid fatty acid profiles of the litter as it degrades, which tells us something about the dominant microbial taxonomic groups present in the litter and their response to environmental drivers like UV, soil mixing, and water availability. We are currently expanding this work onto the European continent, looking at the role of UV in litter decomposition in cork oak woodlands in Portugal that are being invaded by a native shrub -Cistus ladanifer.
Collaborators: Steve Archer (University of Arizona), Dave Breshears (University of Arizona), Heather Throop (New Mexico State University), Paul Barnes (Loyola University New Orleans)
Both the Arizona and Portugal field decomposition projects have ended. Lab work, data analysis, and manuscript development continue.
Associated Manuscripts:
Barnes, P.W., H.L. Throop, S.R. Archer, D.D. Breshears, R.L. McCulley, and M.A. Tobler. 2015. Sunlight and soil-litter mixing: drivers of litter decomposition in drylands. Progress in Botany 76:273-302. doi: 10.1007/978-3-319-08807-5_11
Lee, H., J. Fitzgerald, D.B. Hewins, R.L. McCulley, S.R. Archer, T. Rahn, and H.L. Throop. 2014. Soil moisture and soil-litter mixing effects on surface litter decomposition: A controlled environment assessment. Soil Biology & Biochemistry 72:123-132.
Hewins, D., S. Archer, G. Okin, R.L. McCulley, and H. Throop. 2013. Soil-litter mixing accelerates decomposition in a Chihuahuan Desert grassland. Ecosystems 16:183-195.
Please contact Rebecca for copies.
Consequences of Long-Term Agriculture and Grassland Restoration in the Tallgrass Prairie Region of North America
Tallgrass prairie soils are thought to have historically contained some of the largest soil carbon stocks in North America. In part because of these high fertility soils, more than 99% of this region has been converted to row-crop agriculture over the past 150 years. Traditional agricultural techniques are thought to reduce soil C pools by 30-50%, leading to the hypothesis that significant soil C sequestration will occur if agricultural practices are stopped and grassland communities are restored. We tested this hypothesis at 5 locations (Texas, Kansas, 2 sites in Iowa, and Minnesota). We also assessed the effects of long-term agriculture and grassland restoration on soil microbial communities. At all locations, native, uncultivated tallgrass prairie had significantly more soil C than all other land use types; however, we found that neither soil C nor microbial communities responded to grassland restoration in a consistent manner. Some sites gained soil C over time with grassland restoration, and the microbial communities converged to those of adjacent native prairie, consistent with the goals of restoration. However, others had no appreciable increase or clearly identifiable change in the microbial community. Understanding the effects of land use change in this region may be more difficult than has been previously realized.
Metagenomic microbial work illustrates that Verrucomicrobia are important in native tallgrass prairie soils, perhaps due to high amounts of relatively recalcitrant carbon. Understanding the effects of land use change and restoration on soil microbes and ecosystem function in this region may be more difficult than has been previously realized.
Collaborators: Noah Fierer (Univ. of Colorado – Boulder); Rob Jackson (Stanford University)
Associated Manuscripts:
Sanderman, J., T. Hangl, and G.J. Fiske. 2017. Soil carbon debt of 12,000 years of human land use. PNAS 114: 9575-9580. (This paper used the soil C data collected in this project to validate its model projections.)
Fierer, N., J. Ladau, J.C. Clemente, J.W. Leff, S.M. Owens, K.S. Pollard, R. Knight, J.A. Gilbert, and R.L. McCulley. 2013. Reconstructing the microbial diversity and function of pre-agricultural tallgrass prairie soils in the United States. Science 342:621-624.
Please contact Rebecca for copies.
Native Warm Season Grassland Restoration
There are a variety of separate projects in our lab that deal with native grassland restorations and also incorporate tall fescue and its fungal endophyte symbiosis. Former PhD student, Sarah Hall, completed her dissertation on this topic. Sarah conducted three studies to examine whether endophyte-infected (E+) tall fescue plants respond differently to restoration management than endophyte-free (E-) plants, and whether the success of planted native species might be impacted via indirect soil effects. She found little evidence that endophyte infection status altered tall fescue effects on restoration success (Hall et al.2012). Ben Leffew, a former MS student, added to Sarah's work by exploring how spatial patterns of tall fescue cover vary across an 80 acre pasture currently undergoing native warm season grassland restoration and whether fescue cover post-restoration is correlated with environmental factors, such as depth to bedrock, soil nutrient availability and texture, biotic factors (e.g., rodent granivory and pre-restoration fungal endophyte infection frequency within the tall fescue community), or restoration management factors (e.g., heat of fire during burning, variability in herbicide application, and/or native reseeding success). We have been involved with similar work occurring in the Grand River Grasslands of southwestern Iowa for a few years now as well. Here, tall fescue is officially considered invasive, and managers try to control it by using patch-burn grazing (also called pyric herbivory). In this project, we are investigating the potential of the fire and grazing interaction to alter endophyte infection rates of tall fescue and/or reduce tall fescue abundance and therefore mitigate symptomatic fescue toxicosis of cattle grazing pastures invaded by tall fescue. Collaborators on the project are also monitoring effects of patch-burn grazing on plant community, bird and insect diversity.
Associated Manuscripts:
Ruffner, M.E., R.L. McCulley, J.A. Nelson, and T.G. Barnes. 2012. Invasion by exotic Old World bluestem grasses alters ecosystem function of a South Texas coastal prairie. Biological Invasions 14:1483-1500.
Hall, S.L., R.L. McCulley, and R.J. Barney. 2012. Restoration of native warm season grassland species in a tall fescue pasture using prescribed fire and herbicides. Restoration Ecology 20:194-201.
Please contact Rebecca for copies.
Woody Plant Dominance in Grasslands Alters Ecosystem Dynamics
Woody plant dominance in grasslands can dramatically alter ecosystem structure and function. I have examined the effects of woody plant encroachment on soil nutrient pools and microbial communities in south Texas (McCulley et al. 2004, 2007), in central Texas (McCulley and Jackson 2012), and in sites throughout the southwestern U.S. (McCulley et al., 2004). We are currently involved in work addressing this topic in the Iberian Peninsula, where a native woody shrub, Cistus ladanifer, is invading annual grassland dominated cork oak savannas (shown above). Rebecca and Jim spent half of 2014 on sabbatical in Portugal to continue this work and to assess effects of pasture biodiversity renovations on C, N, P stoichiometry in cork oak savannas.
Do expected evolutionary trade-offs in enzyme activities manifest at the level of microbial community function?
Enzymes are proteins that catalyze (i.e. increase the rates of) chemical reactions. There are many different enzymes in the cells of all living things. And in all living things, including animals, plants and bacteria, there are enzymes that catalyze the process of respiration. This process takes complex organic compounds, such as sugars and fats, and breaks them into simpler forms to create energy. A by-product of respiration is carbon dioxide. For many organisms, the speed at which respiration occurs, and hence at which carbon dioxide is produced, increases as temperature increases. For this reason there is concern that bacteria and fungi in soils, where much of the world’s carbon is stored, will consume more soil carbon and respire more carbon dioxide to the atmosphere under global warming. If this occurs it may result in more rapid warming of the planet. There is much uncertainty as to whether this positive feedback to global warming will happen - in part because living things can produce different types of respiratory enzymes as temperatures change and not all enzymes may be similarly responsive to changing temperatures. As it gets warmer, they may produce enzymes that reduce respiration rates and cause the planet to warm more slowly than some predictions suggest.
This project tests whether bacteria and fungi in soils maintain initial increases in respiration rates when temperatures rise, or whether over time they decrease respiration rates in a way that is consistent with a change in the production of enzymes to those that slow respiration. To look at the bacteria and fungi in soils, the project will use DNA-sequencing and fatty-acid profiling methodologies. To determine respiration rates, carbon dioxide production from the soils will be measured using gas-analysis techniques. To generate differences in temperatures to which bacteria and fungi have been exposed, soils will be collected across a gradient from the arctic to the tropics, in winter and in summer, and also incubated in the laboratory at different temperatures.
All samples and incubations for this work are complete. Data are currently being analyzed and written up.
Collaborators: Mark Bradford (Yale University), Noah Fierer (Univ. of Colorado-Boulder)
Associated Manuscripts:
Smets, W., J.W. Leff, M.A. Bradford, R.L. McCulley, S. Lebeer, N. Fierer. 2016. A method for simultaneous measurement of soil bacterial abundances and community composition via 16S rRNA gene sequencing. Soil Biology & Biochemistry. 96: 145-151.
Strickland, M.S., R.L. McCulley, J.A. Nelson, and M.A. Bradford. 2015. Compositional differences in root exudates elicit a limited functional and compositional response in soil microbial communities. Frontiers in Microbiology 6:817. doi: 10.3389/fmicb.2015.00817
Crowther, T., D. Maynard, J. Leff, E. Oldfield, R.L. McCulley, N. Fierer, M. Bradford. 2014. Predicting the responsiveness of soil biodiversity to deforestation: a cross-biome study. Global Change Biology 20(9):2983-2994. doi: 10.111/gcb.12565
Please contact Rebecca for copies.