Abstract. The cycling of carbon (C) between the Earth surface and
the atmosphere is controlled by biological and abiotic processes that
regulate C storage in biogeochemical compartments and release to the
atmosphere. This partitioning is quantified using various forms of C-use
efficiency (CUE) – the ratio of C remaining in a system to C entering that
system. Biological CUE is the fraction of C taken up allocated to
biosynthesis. In soils and sediments, C storage depends also on abiotic processes, so the term C-storage
efficiency (CSE) can be used. Here we first review and reconcile CUE and CSE
definitions proposed for autotrophic and heterotrophic organisms and
communities, food webs, whole ecosystems and watersheds, and soils and
sediments using a common mathematical framework. Second, we identify general
CUE patterns; for example, the actual CUE increases with improving growth
conditions, and apparent CUE decreases with increasing turnover. We then
synthesize > 5000 CUE estimates showing that CUE decreases with
increasing biological and ecological organization – from unicellular to
multicellular organisms and from individuals to ecosystems. We conclude that
CUE is an emergent property of coupled biological–abiotic systems, and it
should be regarded as a flexible and scale-dependent index of the capacity of
a given system to effectively retain C.
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