Neon's Strategy for Measuring Soil Climate, Respiration, and Root Turnover.

Climate change, land use change, and invasive species, are expected to alter soil climate and biological activity throughout the US over coming decades. Changes in soil properties will result from direct impacts as well as indirect pathways caused by aboveground-belowground interactions and feedbacks. The National Ecological Observatory Network (NEON) will monitor soil and other ecosystem properties at 60 sites throughout the US for 30 years to identify and enable forecasting of the impacts of human activities on ecosystems. Soil measurements at these sites fall into two broad categories: 1) in-situ sensor measurements with high temporal frequency, but limited spatial coverage; and 2) laboratory-based measurements with lower temporal frequency, but greater spatial coverage. Here, we provide an overview of NEON’s in-situ soil sensor sampling design. Each NEON site includes 5 sensor-based soil plots co-located with other observations to facilitate linkages among belowground, aboveground, and atmospheric measurements. Soil measurements within these plots will include temperature and moisture profiles to 2 m, heat flux, respiration rate, and fine root turnover using minirhizotrons. Several strategies have been employed to ensure that measurements are representative at different spatial scales, including 1) using soil horizons to guide sensor depths, 2) quantifying local scale spatial variability to inform plot spacing, 3) using soil maps to ensure locally dominant soil types are represented, and 4) using ecoclimatic variables to inform site location at the continental scale. Initial findings revealed that every major US soil order is represented, and geospatial analyses indicate that at the local scale soil measurements will be at least 90% spatially independent at 77% of sites. Finally, a similar suite of soil sensors will also be included in NEON’s Mobile Deployment Platform, which will be used to study targets of opportunity (e.g., recovery following a wildfire) and can be requested for PI-driven research.