Biomass Distribution on Earth

Introduction to Biomass Distribution on Earth

  • Authors and Institutions:

    • Yinon M. Bar-On, Rob Phillips, Ron Milo

    • Affiliated Departments:

    • Weizmann Institute of Science, Israel

    • California Institute of Technology, USA

  • Background:

    • Understanding biomass (the living matter on Earth) is essential for studying biosphere structure and dynamics.

    • A quantitative comparison of biomass among different taxa is currently lacking.

  • Objective:

    • Assemble a comprehensive census of the biomass composition of the biosphere, estimated at approximately 550 Gt C (gigatons of carbon).

Key Findings

  • Distribution Among Major Taxa:

    • Plants: ≈450 Gt C (dominant kingdom, primarily terrestrial).

    • Animals: ≈2 Gt C (mainly marine).

    • Bacteria: ≈70 Gt C (predominantly deep subsurface).

    • Archaea: ≈7 Gt C (also mainly located in deep subsurface environments).

    • Terrestrial Biomass: Two orders of magnitude higher than marine biomass.

    • Total marine biota estimated at ≈6 Gt C, double previous estimates.

    • Global marine biomass pyramids show more consumers than producers.

  • Human Biomass Impact:

    • Human biomass (≈0.06 Gt C) exceeds that of all wild mammals combined.

    • Historical impact of humanity analyzed through biomass data of mammals, fish, and plants.

Historical Context and Research Foundation

  • Importance of Quantifying Biomass:

    • Essential for biosequestered carbon calculations and modeling global biogeochemical cycles.

  • Previous Studies:

    • Earlier estimates primarily focused on plants.

    • Prokaryotic biomass highlighted in Whitman et al. (1998) as a major component.

    • Recent technological advances (e.g., next-gen sequencing, remote sensing) allow for improved biomass quantification.

  • Comparison to Older Efforts:

    • Whittaker and Likens (1970s) provided early estimates that are now considered outdated; lacked comprehensive data on prokaryotes.

    • Smil (2013) contributed a section on biomass in a broader book that remains less integrated.

Methods and Data Collection

  • Biomass Data Estimation:

    • Analysis based on hundreds of studies with updated estimates for multiple taxa.

    • Ongoing sampling campaigns (e.g., Tara Oceans, National Ecological Observatory Network) are essential for current assessments.

  • Mathematical and Statistical Techniques:

    • Estimates reported in Gt C, independent of water content.

    • Conversion factors introduced (1 Gt C = 10^15 g of carbon).

  • Data Visualization:

    • Figure representations (Voronoi diagrams) used to illustrate biomass distributions across taxa.

Biomass Estimates Summary

  • Total Biomass Composition:

    • Plants: 450 Gt C, 80% of total

    • Bacteria: 70 Gt C, 15% of total

    • Fungi: 12 Gt C

    • Archaea: 7 Gt C

    • Protists: 4 Gt C

    • Animals: 2 Gt C

    • Viruses: 0.2 Gt C

  • Aboveground vs. Belowground Biomass:

    • Aboveground: ≈320 Gt C (≈60% of global biomass).

    • Belowground: mainly plant roots (≈130 Gt C) and soil microbes (≈100 Gt C).

Uncertainties in Biomass Estimates

  • Variability:

    • Estimates of bacteria are uncertain, yet they constitute ≈15% of total biomass.

    • Fungi are less influential than anticipated compared to their biodiversity presence.

    • Uncertainties arise from differences in measurement methodologies and data sources.

Human Impact on Biomass

  • Increase in Human and Livestock Biomass:

    • Human and livestock biomass surpasses that of wild fauna significantly.

  • Historical Consequences:

    • Involvement in Quaternary Megafauna Extinction reduced the mass of land mammals dramatically.

    • Current wild land mammal biomass is ≈0.003 Gt C, significantly lower than pre-human estimates.

Comparative Analysis of Biomass Between Environments

  • Terrestrial vs. Marine:

    • Land biomass ≈470 Gt C, two orders higher than marine biomass at ≈6 Gt C.

    • Primary productivity is similar across both environments, despite differences in biomass.

    • Majority of animal biomass in marine environments, with microorganisms prevalent in depth.

Biomass by Trophic Levels

  • Trophic Modes:

    • Terrestrial primary producers have greater biomass than consumers.

    • Marine environments exhibit inverted biomass pyramids, where consumer biomass exceeds that of producers.

    • Observations on biomasses of planktonic communities further indicate this trend.

Gaps in Current Knowledge and Future Directions

  • Need for Further Research:

    • Emphasis on diverse environmental sampling to enhance understanding of biomass distribution.

    • Potential improvements to estimates of prokaryotic biomass and other microscopic taxa.

    • Consideration of the role of parasites in overall biomass assessment.

  • Unified Global View:

    • The study aims to disseminate knowledge and understanding of biomass composition for researchers and students alike.