RUSSELL REVIEW Soil carbon stewardship: Thinking in circles

The words we choose to describe our research ultimately directs its course. A dominant term in soil science now, is ‘sequestration’, referring to the removal of carbon (C) from air and its irreversible seclusion in soil, ideally as stable soil organic carbon (SOC). An emerging view, however, now sees SOC as an inherently dynamic assemblage of forms, all potentially vulnerable to decay, with no discrete, measurable fraction holding C in ‘sequestered’ form. Rather than speaking of C ‘sequestration’, then, we might refer instead to SOC ‘stewardship’. This word, now, enfolds the entire spectrum of SOC, not merely some elusive ‘persistent’ or ‘stable’ fraction, perhaps redirecting inquiry; for example, does C need to be ‘sequestered’ in stable form for SOC to serve as effective repository of excess atmospheric CO₂? ‘Stewardship’ explicitly accepts the relentless turnover of SOC, emphasizing the need to manage not only fixed stocks of C, but also the cyclical flows of C through ecosystems that drive their functions. Among other benefits, ‘stewardship’ might motivate us to consider all functions of SOC (not only climate mitigation), consider the entire C cycle (not only enhancing soil C), and preserve existing troves of SOC (not only augmenting them in selected places.) Perhaps most fundamentally, by its etymology, ‘stewardship’ poses a compelling, timeless question: for whom do we steward SOC? Asking why look after SOC, not only reflects our own underlying quest for resilience, but also expands our potential audience and entices the more creative minds that must succeed us. Although ‘stewardship’ may elicit new and fruitful inquiry, we may need to look for words even more evocative, more alluring, more true to our mandate of living well within the circling C that must always sustain us.