Reconciling carbon‐cycle processes from ecosystem to global scales

Abstract

C arbon (C) is the building block of life. Global photosynthesis generates approximately 100 terawatts (TW) of energy each year by converting solar radiation into stored chemical energy (Barber 2009). Photosynthesis also represents the largest global annual C flux, of ~125 petagrams (Pg; where 1 Pg equals 10 15 grams [g] and 1 Pg C is roughly equivalent to 0.47 parts per million [ppm] of CO 2), with the second greatest flux consisting of the subsequent release of CO 2 via respiration (~122 Pg C/year). Both of these fluxes are an order of magnitude greater than fossil-fuel emissions (Ballantyne et al. 2015). The atmospheric CO 2 that is fixed during photosynthesis is subsequently stored and transferred as chemical energy, which in turn fuels the metabolic reactions of most autotrophs and heterotrophs. Although C is the most common element in the terrestrial biosphere, representing approximately 50 parts per hundred (%) of all organic matter, CO 2 represents only a very small fraction of the atmosphere and is therefore measured in ppm (~415 ppm in 2020). Given the abundance of C in the terrestrial biosphere and the massive fluxes of C occurring between the biosphere and the atmosphere, it is no surprise that scientists have developed a myriad of innovative ways for measuring and simulating C-cycle processes across a range of scales in time and space. For example, chloroplast CO 2 fluxes are estimated over millimeters per second, whereas biome CO 2 fluxes may be estimated over thousands of kilometers per year. There have been many advances in C-cycle science over the past 60 years at leaf, plant, ecosystem, and global scales, but both challenges to and opportunities for scientific advancement remain. Progress is necessary, however, especially at the macrosystem scale, where human management and ecological processes are often at odds and create interesting interactions of C dynamics. One of the greatest impediments to accurate predictions of future climate is the uncertain response of the terrestrial C cycle to impending changes in temperature, precipitation, and atmospheric CO 2 concentrations (Friedlingstein et al. 2013). Even though land-surface models have become increasingly realistic in their mechanistic representation of C-cycle processes by including nutrient limitation (Thornton et al. 2007),

Macrosystems revisited: challenges and successes in a new subdiscipline of ecology

“…Fei et al (2018), for instance, demonstrated that the biodiversity-productivity relationship changes across a large spatial extent, with climatic variation as the underlying determinant, while Read et al (2018) used continental-scale monitoring of small mammal populations to demonstrate how trait space can explain increased diversity at lower latitudes. Macrosystems biology is also poised to test other long-standing hypotheses, such as scaling interactions across the regional and global biosphere (see Ballantyne et al 2021). Contemporary tools (eg national and independent sensor networks, remote sensing, citizen-science programs) provide new opportunities for assessing previously untestable concepts and hypotheses.…”

“…Macrosystems biology or similar approaches will continue to be relevant to ecological science because small-scale methodologies do not typically upscale readily and therefore fail to adequately capture or describe large-scale spatial patterns. For example, small-scale approaches do not capture properties such as teleconnections (see Tromboni et al 2021), and mesoscale C flux can be difficult to connect to larger scale approaches (see Ballantyne et al 2021). Macrosystems biology offers a distinctive approach that could provide valuable ecological understanding in much the same way that long-term approaches uncovered "ecological surprises" (Dodds et al 2012).…”

“…Macrosystems biology is also poised to test other long‐standing hypotheses, such as scaling interactions across the regional and global biosphere (see Ballantyne et al . 2021). Contemporary tools (eg national and independent sensor networks, remote sensing, citizen‐science programs) provide new opportunities for assessing previously untestable concepts and hypotheses.…”

“…Articles in this Special Issue underscore these points; some societally relevant topics include understanding C cycling across large to small spatial scales at a time when atmospheric concentrations of carbon dioxide (CO 2 ) are exceedingly high (Ballantyne et al . 2021), and the maintenance of biodiversity is coupled to an understanding of the stability of ecosystems (Patrick et al . 2021).…”

“…2021), and mesoscale C flux can be difficult to connect to larger scale approaches (see Ballantyne et al . 2021). Macrosystems biology offers a distinctive approach that could provide valuable ecological understanding in much the same way that long‐term approaches uncovered “ecological surprises” (Dodds et al .…”