Soil Biogeochemical and Microbial Sampling Soil samples are collected at NEON sites to determine physical properties, nutrient stocks, nitrogen (N) transformations, and microbial biodiversity and function. Soil data are used to quantify the stocks of soil carbon (C) and nutrients to understand ecosystem nutrient status, the isotopic (C and N) composition of the soil to gain a picture of integrated ecosystem processes, soil N transformations to understand the rates of microbially-mediated processes, and microbial biomass and community composition. Additionally, NEON characterizes soil pH and volumetric water content, which are some of the environmental controls on biogeochemical processes. Soil cores (6 cm diameter x 30 cm deep) are collected at pre-determined locations within select Tower and Distributed Plots at SRER. Soil biogeochemical stocks and stable isotopes are measured once every 10 years at 10-15 plots between July and August; during the initial years of Operations sampling, soils will be collected more frequently (e.g., each year) for these analyses as domains get up to speed. Microbial community analysis samples are collected in 8 plots three times per year: during the transition from dry season to wet season, during peak biomass, and during the transition from wet season to dry season. When sampling for soil biogeochemical stocks and stable isotopes occurs, soil for microbial analysis is collected at 10-15 plots instead of 8; soil for microbial analyses will be a subsample of the soil core collected for biogeochemical stocks and stable isotopes. Soil N transformation samples are collected once every 5 years: during the transition from dry season to wet season, during peak biomass, and during the transition from wet season to dry season.