Estimating variation in rooting depth and belowground biomass at the continental scale

Abstract:

The production of belowground biomass plays an important role in the total carbon balance and net primary productivity (NPP) of an ecosystem. In particular, fine root biomass, due to rapid turnover rates, contributes a disproportionate amount of annual belowground net primary productivity (BNPP). The NEON Terrestrial Observation System will quantify above- and below-ground biomass at 60 sites distributed across 20 eco-climatic regions. Routine belowground observations include collecting fine root biomass samples to a maximum depth of 30 cm. Because substantial fine root biomass exists below 30 cm, NEON is also characterizing the distribution of fine root biomass with depth down to a maximum of 2 m below the surface in one excavated soil pit per site. The soil pit is dug in the site’s dominant vegetation, and samples are wet sieved to extract roots. In conjunction with physical and chemical properties analyzed within each soil horizon, the soil pit characterization dataset will provide valuable information about the distribution of belowground biomass as a function of depth, as well as differences in total belowground biomass across NEON’s 60 sites.

Here, we analyzed differences in total belowground mass across sites, and we evaluated factors that may contribute to differences in total fine root biomass, such as precipitation, evapotranspiration, soil chemical and physical properties, and aboveground phenology. Soil pit characterization is complete at approximately 50% of sites, and the relatively large sample size allows us to test which factors best predict both the proportion of fine root biomass at depth, as well as total fine root biomass. These characterization data help inform development of NEON data products, and they also illustrate the scope of research possibilities that independent researchers may pursue with free-access to this novel, continental-scale dataset.