Some thoughts on the concept of colimitation: Three definitions and the importance of bioavailability

Abstract

We discuss the concept of colimitation of primary productivity in aquatic environments, with an emphasis on reconciling this concept with recent advances in marine bioinorganic chemistry. Colimitations are divided into three categories on the basis of their mathematical formulations and visualizations: type I, independent nutrient colimitation (e.g., N and P); type II, biochemical substitution colimitation (e.g., Co and Zn); and type III, biochemically dependent colimitation (e.g., Zn and C), where the ability to acquire one nutrient is dependent upon sufficient supply of another. The potential for colimitation occurring in the marine environment and the critical importance of understanding nutrient bioavailability are discussed.

Diagnosing oceanic nutrient deficiency

“…Moreover, again within a stoichiometrically conserved system, once limitation by the most deficient nutrient develops, the other nutrients would be expected to remain replete [9,25]. However, such arguments can break down once the potential for flexibility in the stoichiometric coupling of different nutrient cycles is acknowledged [11,18,28,33].…”

“…The significance of any distinction between such so-called 'rate'- [8] or 'yield'-type [9] limitations, respectively, will be explicitly acknowledged where relevant in the context of what follows. However, it is worth noting that the two concepts may frequently be linked [18]. For example, the overall biomass of a community would not be expected to respond to an increased supply of a limiting nutrient unless the production of some component of the community were previously rate limited by the availability of that nutrient [11].…”

“…ratios of the different nutrients within a microbial cell are known, a nutrient can be considered deficient within the extracellular environment if the concentration or supply of this nutrient is low relative to all the others [11,18]. Thus, for example, two different water masses having dissolved N : P ratios of 20 : 1 and 14 : 1, i.e.…”

“…Nutrient deficiency can thus be considered as indicative of the potential for ('Liebig-type' [9]) nutrient limitation to develop [18]. Within a strictly stoichiometrically conserved system, i.e.…”

“…Fe, Mn, Zn, Ni, Cu, Co and Cd) is profoundly influenced by biological processes, while some may also have the potential to reciprocally influence upper ocean microbiological processes [2,11,12]. Indeed, despite the long hiatus between the earliest suggestions that Fe limitation may be an important process in oceanic systems and development of the analytical techniques which made rigorous investigation of this problem possible [16], the potential for trace metal (co-)limitation of phytoplankton productivity is now firmly established [11,[17][18][19]. The advent of the high-quality global-scale datasets which are emerging as a result of the international GEOTRACES project [20] promises to be further transformative in our understanding of the linked biogeochemical cycles of multiple nutrients in oceanic systems.…”