This is a linkpost for The metabolic rate of the biosphere and its components by Tori M. Hoehler, Dylan J. Mankel, Peter R. Girguis, Thomas M. McCollom, Nancy Y. Kiang, and Bo Barker Jørgensen, which was originally published in the Proceedings of the National Academy of Sciences on 12 June 2023. Below are the significance, abstract, and some parts I found interesting. I very much liked the article because I think individual (expected hedonistic) welfare per fully-healthy-organism-year might be proportional to “metabolic energy consumption per unit time at rest at a given temperature”^“exponent”. The metabolic energy consumption per unit time at rest is called basal metabolic rate for endothermic animals.

Significance

Assessing the relationship between energy flux and the quantity of biomass it sustains offers the potential to understand the biological “carrying capacity” for ecosystems on Earth and beyond. Our work supports this understanding by quantifying the energy–biomass relationship for the global biosphere and an environmentally diverse range of its components, and by exploring the factors—including the impact of humanity—that affect that relationship.

Abstract

We assessed the relationship between rates of biological energy utilization and the biomass sustained by that energy utilization, at both the organism and biosphere level. We compiled a dataset comprising >10,000 basal, field, and maximum metabolic rate measurements made on >2,900 individual species, and, in parallel, we quantified rates of energy utilization, on a biomass-normalized basis, by the global biosphere and by its major marine and terrestrial components. The organism-level data, which are dominated by animal species, have a geometric mean among basal metabolic rates of 0.012 W (g C)^-1 and an overall range of more than six orders of magnitude. The biosphere as a whole uses energy at an average rate of 0.005 W (g C)^-1 but exhibits a five order of magnitude range among its components, from 0.00002 W (g C)^-1 for global marine subsurface sediments to 2.3 W (g C)^-1 for global marine primary producers. While the average is set primarily by plants and microorganisms, and by the impact of humanity upon those populations, the extremes reflect systems populated almost exclusively by microbes. Mass-normalized energy utilization rates correlate strongly with rates of biomass carbon turnover. Based on our estimates of energy utilization rates in the biosphere, this correlation predicts global mean biomass carbon turnover rates of ~2.3 y^-1 for terrestrial soil biota, ~8.5 y^-1 for marine water column biota, and ~1.0 y^-1 and ~0.01 y^-1 for marine sediment biota in the 0 to 0.1 m and >0.1 m depth intervals, respectively.

Power and MSP at the Organism Level.

Fig. 1 presents “snapshots” from the Supplementary Interactive Plot of metabolic power vs. mass (Fig. 1A) and mass-specific metabolic power (MSP) vs. mass (Fig. 1B) for a specific configuration that includes basal rates only, with no temperature normalization, and using carbon-based mass units. Fig. 1A shows that the basal metabolic power of individuals scales with carbon biomass (g) across ~22 orders of magnitude (<10^-14 to >10⁷ g C) according to a power law:

Fig. 1.

The exponent, k = 0.95 ± 0.003, is close to unity and shows that the metabolic rates vary nearly proportionally to the biomass of the organisms, when viewed over the entire tree of life. This stands in contrast to the well-documented scaling of basal metabolic rates with mass in some taxa such as mammals (k = 0.73), birds (k = 0.67 to 0.74), fishes (k = 0.86), and insects (k = 0.66) (e.g., refs. 11–13 [relatedly, see Kleiber's law]). Within these taxa, metabolic power increases relatively less than the increase in biomass. These trends become clearer when metabolic power is normalized to body mass (Fig. 1B). Among the mammals or birds, mass-specific metabolic power (MSP) exhibits a systematic 100-fold decrease with increasing body mass, from pygmy shrew to blue whale or from hummingbird to ostrich.

Power and MSP at the Biosphere Level.

Table 1. Estimates of mass (Pg = 10¹⁵ g), power (TW = 10¹² Watt), and MSP for the global biosphere

The global photosynthetic biosphere harnesses about 2,800 TW of light energy via photosynthesis (i.e., as “photon capture”), which is ~3% of the global full spectrum solar irradiance at Earth’s surface and ~7% of the available photosynthetically active radiation (PAR). The combined gross primary productivity (GPP) of marine and terrestrial primary producers, about 220 to 340 Pg C y^-1 (20, 21), represents a chemical energy flux of 280 TW when utilized in respiration, of which 170 TW is attributable to autotrophic respiration in phototrophs and 110 TW is attributable to heterotrophic respiration by Earth’s nonphotosynthetic biota*.