Global Distribution of Fine Root Biomass in Terrestrial Ecosystems

A global data set of root biomass, rooting profiles, and nutrient concentrations in roots was compiled from the primary literature and used to study distributions of root properties. This data set consists of ninety estimates of live and total fine root biomass associated with Table 1 published in Jackson et al. (1977) (Jackson, R. B., H. A. Mooney, and E.-D. Schulze. 1997. A global budget for fine root biomass, surface area, and nutrient contents. Proceedings of the National Academy of Sciences, U.S.A. 94:7362-7366). Expanded data on rooting profiles and nutrients are available in other data sets; however, these data represent a unique tabulation of fine root measurements. Understanding and predicting ecosystem functioning (e.g., carbon and water fluxes) and the role of soils in carbon storage requires an accurate assessment of plant rooting distributions. Here, in a comprehensive literature synthesis, we analyze rooting patterns for terrestrial biomes and compare distributions for various plant functional groups. The initial data set (Jackson et al. 1996) was expanded to examine distributions of root budgets (Jackson et al. 1997). Measurements were selected from over 300 field studies. Results from the analysis showed that calculated root surface area is almost always greater than leaf area, more than an order of magnitude so in grasslands. The average C:N:P ratio in living fine roots is 450:11:1, and global fine root carbon is more than 5 percent of the magnitude of all carbon contained in the atmosphere. Assuming conservatively that fine roots turn over once per year, they represent 33 percent of global annual net primary productivity. A PDF copy of the Jackson et al (1996) paper is available at http://www.biology.duke.edu/jackson/oecol96c.pdf, and a PDF copy of the Jackson et al. (1997) paper is available on-line at http://www.biology.duke.edu/jackson/PNAS97.htm. This data set has been expanded and updated over the years to estimate root turnover rates (data for approximately 341 site-vegetation combinations for 188 site from 152 papers in Gill and Jackson 2000); studies of root nutrient concentrations (data for approximately 372 site-pit-depths from 57 papers in Gordon and Jackson 2000); and rooting depth (data for approximately 298 sites with 565 profiles in Schenk and Jackson 2002). The three recent papers include most of the data contained in the initial root data set; however, some observations may have been excluded because of more stringent selection criteria. Many of the source papers provided data for the three recent rooting papers and users are encouraged to review the three recent data sets. The file described at http://www-eosdis.ornl.gov/VEGETATION/guides/fine_roots_biomass.html that provides estimates of both live and total fine root biomass for approximately 100 sites is unique to the collection of four data sets of root characteristics developed by Jackson and his collaborators. The Oak Ridge National Laboratory Distributed Active Archive Center (ORNL DAAC) for Biogeochemistry Dynamics organized and formatted these data for long-term archive. Spreadsheet files are stored as ASCII tab-delimited files. Missing values are represented by -999.