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The seventh macronutrient: how sodium shortfall ramifies through populations, food webs and ecosystems
Author(s) -
Kaspari Michael
Publication year - 2020
Publication title -
ecology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.852
H-Index - 265
eISSN - 1461-0248
pISSN - 1461-023X
DOI - 10.1111/ele.13517
Subject(s) - herbivore , biology , ecology , trophic level , detritivore , sodium , ecosystem , limiting , omnivore , palatability , abundance (ecology) , lawn , predation , chemistry , food science , mechanical engineering , organic chemistry , engineering
Of the 25 elements required to build most organisms, sodium has a unique set of characteristics that ramify through terrestrial ecology. In plants, sodium is found in low concentrations and has little metabolic function; in plant consumers, particularly animals, sodium is essential to running costly Na‐K ATPases. Here I synthesise a diverse literature from physiology, agronomy and ecology, towards identifying sodium’s place as the ‘7th macronutrient’, one whose shortfall targets two trophic levels – herbivores and detritivores. I propose that sodium also plays a central, though unheralded role in herbivore digestion, via its importance to maintaining microbiomes and denaturing tannins. I highlight how sodium availability is a key determinant of consumer abundance and the geography of herbivory and detritivory. And I propose a re‐appraisal of the assumption that, because sodium is metabolically unimportant to most plants, it is of little use. Instead, I suggest that sodium’s critical role in limiting herbivore performance makes it a commodity used by plants to manipulate their herbivores and mutualists, and by consumers like bison and elephants to generate grazing lawns: dependable sources of sodium.