This collection contains oven-dried belowground biomass samples from Tower plots (NEON sample class: bbc_chemistryPooling_in.bgcArchiveID). At each terrestrial NEON site, roots are sampled from base plots (20-30) within the tower airshed (Tower plots) every five years. In each Tower plot, one or two clip cells (depending on plot size) are randomly chosen out of the pre-determined clip cell locations for root coring. The same clip cells are also used for annual aboveground Herbaceous Biomass sampling. In 20m x 20m Tower plots, two soil cores are sampled from one clip cell per bout. In 40m x 40m Tower plots soil core sampling occurs in two (out of four) randomly assigned 20m x 20m subplots, and two soil cores are sampled from one clip cell per subplot per bout. A root core is taken to 30 cm maximum depth from both the northern and southern end of the clip cell. Samples are cored to 30 cm depth in order to be consistent with the sampling depth used for soil biogeochemistry and microbe sampling. All roots are sorted into three size category bins: <1 mm, 1-2 mm, and 2-10 mm, and dry mass is recorded. Sorting to live/dead was initially attempted but suspended in early 2019; sorting to species is not attempted. Biomass per size category is pooled by clip strip prior to chemistry analysis and archive. If there is enough root sample to archive, the material is oven-dried at 65 degrees Celsius for at least 48 hours, ground in a Wiley mill to 20 mesh size (sieve opening size = 0.0331 in), then transferred to a 20 mL HDPE scintillation vial and stored at room temperature. See link below for the NEON data product that provides mass as well as carbon and nitrogen concentrations and stable isotopes of these same root samples.