Linking plants, soil, and microbes: Geomorphic and ecological stability in the Nebraska Sand Hills

As recently as 800 yrs ago, the Nebraska Sand Hills lost grass cover and became an active dune field. Although climate ultimately drives geomorphic stability in this semi-arid landscape, the plant-soil system controls the stability of the sand surface. The Grassland Destabilization Experiment (GDEX) began in 2004 and has four treatments: control, grazed, pulse disturbance (vegetation killed one growing season), and press disturbance (vegetation killed for length of study). While pulse plots test resilience, or the ability to recover from short-term disturbance, press plots test resistance, or the ability to maintain system functioning given long-term shifts in system drivers. Data collected in GDEX include above- and belowground plant biomass, microbial biomass and community profiles (FAME), soil respiration, soil nitrate and ammonium dynamics, soil carbon and nitrogen, soil moisture, and sand movement. Press and pulse plots were killed in May 2005. In these treatments, root biomass was reduced 60% and soil respiration 40% when compared to control plots in October 2005. Soil moisture and nitrate levels increased significantly through 2005 in dead plots. The early 2006 growing season was dry, with significantly reduced plant production and soil respiration in control plots compared to 2005. Nevertheless, pulse plots revegetated in 2006 with annuals and exceeded the aboveground biomass of control grasslands by late summer. Press plots remained dead in 2006, and had approximately 30% of the root biomass and 40% of the soil respiration observed in control plots. As of November 2006, significant sand movement had not occurred in either disturbance treatment.