CARBON SEQUESTRATION IN ECOSYSTEMS: THE ROLE OF STOICHIOMETRY

TLDR

Carbon fate in ecosystems is governed by mass‑balance and nutrient stoichiometry, with autotrophs and heterotrophs exhibiting different C:element ratios that shape C‑use efficiency and determine how much carbon is diverted to detritus and soils. The article examines how these stoichiometric principles drive carbon sequestration across aquatic and terrestrial ecosystems, emphasizing the evolutionary pressure to channel excess carbon into structural and metabolic functions.

Abstract

The fate of carbon (C) in organisms, food webs, and ecosystems is to a major extent regulated by mass-balance principles and the availability of other key nutrient elements. In relative terms, nutrient limitation implies excess C, yet the fate of this C may be quite different in autotrophs and heterotrophs. For autotrophs nutrient limitation means less fixation of inorganic C or excretion of organic C, while for heterotrophs nutrient limitation means that more of ingested C will “go to waste” in the form of egestion or respiration. There is in general a mismatch between autotrophs and decomposers that have flexible but generally high C:element ratios, and consumers that have lower C:element ratios and tighter stoichiometric regulation. Thus, C-use efficiency in food webs may be governed by the element ratios in autotroph biomass and tend to increase when C:element ratios in food approach those of consumers. This tendency has a strong bearing on the sequestration of C in ecosystems, since more C will be diverted to detritus entering soils or sediments when C-use efficiency is low due to stoichiometric imbalance. There will be a strong evolutionary pressure to utilize such excess C for structural and metabolic purposes. This article explores how these basic principles may regulate C sequestration on different scales in aquatic and terrestrial ecosystems.