The seventh macronutrient: how sodium shortfall ramifies through populations, food webs and ecosystems

Abstract

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.

Environmental Nutrients Alter Bacterial and Fungal Gut Microbiomes in the Common Meadow Katydid, Orchelimum vulgare

“…Recently, the rise in the research interest on insect microbiomes has helped reveal novel insights and understanding of insect ecology. Both resident and transient microbes exhibited effects on the health and fitness of their insect hosts (McKenney et al, 2018), such as improved nutrition (Brune, 2014;Paniagua Voirol et al, 2018), changes to host behaviors (Dillon et al, 2000), increased reproductive success (Kaltenpoth et al, 2009), and protection from environmental pathogens and pesticides (Paniagua Voirol et al, 2018). Conversely, behaviors of the insect host like feeding and social roles can be reflected in variations in their microbiome (Yun et al, 2014;Jones et al, 2018;Kakumanu et al, 2018;Obadia et al, 2018).…”

Micronutrients enhance macronutrient effects in a meta‐analysis of grassland arthropod abundance

“…Finally, if micronutrients are key components that regulate consumer abundance, then understanding which elements are important and precisely how they work is paramount. Progress, using simple addition experiments, has been made along those lines for Na, a micronutrient key to animal health and performance (Borer et al., 2019; Kaspari, 2020; Kaspari, Bujan, et al., 2017; C. M. Prather, Laws, et al., 2018; R. M. Prather, Roeder, et al., 2018; Welti et al., 2019). More such experiments are needed to examine the effects of Ca, Mg, Mo and other micronutrients on grassland arthropod guilds (Kaspari & Powers, 2016).…”

“…Progress, using simple addition experiments, has been made along those lines for Na, a micronutrient key to animal health and performance (Borer et al, 2019;Kaspari, 2020;Kaspari, Bujan, et al, 2017;C. M. Prather, Laws, et al, 2018;R.…”

Sexual Dimorphism in the Multielemental Stoichiometric Phenotypes and Stoichiometric Niches of Spiders

“…Importantly, the observed patterns suggest that stoichiometric relations between atoms of more elements than the commonly studied C, N and P may shape ecological interactions and the functioning of food webs, which is also confirmed by the results of the limited studies on multielemental ecological stoichiometry published to date (e.g., [8,24,38]). Recently, the role of Na limitation in shaping ecological interactions was emphasized [39]; however, approximately twenty-five elements build molecules driving the functioning of every living organism on Earth, and much research is still needed in the area of multielemental stoichiometry [5,8,29]. This is made even more complicated by the fact that the concentration of every element composing the organismal body influences the concentrations of all other elements, and all of them are strongly interrelated [38].…”