Mycorrhizal symbioses influence the trophic structure of the Serengeti, Stevens 2018

Compendium Volume 2 Number 1 July 2018

Our analysis shows that inputs of phosphorus through arbuscular mycorrhizal symbioses substantially increase the ability of plants to grow and maintain nutritional quality, cascading through the biomass of consumers and predators in the ecosystem. Although they account for less than 1% of the total modelled biomass, the predicted nutritional benefit provided by arbuscular mycorrhizal fungi increased the biomass of macro-organisms in the Serengeti by 48%. When considering the management of biodiversity, future ecosystem models should account for the influence of arbuscular mycorrhizal fungi on all trophic levels [Stevens 2018: 536].

More than 70% of all angiosperm families form AM symbioses (Brundrett, 2009), and these symbioses are often essential for plant nutrition (Marschner & Dell, 1994). Mycorrhizal symbioses also improve plant tolerance to drought (Augé, 2001) and resistance to pathogens (Cameron, Neal, van Wees, & Ton, 2013) [Stevens 2018: 537].

Plant taxa vary in the degree to which they depend upon mycorrhizas; but in general, AM symbioses are essential for the nutrition of tropical plants, and warm season grasses are often highly dependent on mycorrhizas, acquiring up to 90% of their phosphorus requirements from AM fungi [Stevens 2018: 537].

Thirty years ago, McNaughton, Ruess, and Seagle (1988) concluded that large mammals have a major organising effect in the Serengeti ecosystem. From our analysis, we can conclude that AM fungi also play a critical role in the trophic structure of the Serengeti. Our model simulations suggest that although AM fungi account for less than 1% of the total biomass, phosphorus supplied by AM symbioses sustains half the vegetation biomass, and accordingly, half of the biomass of iconic migratory herbivores and one-third of the carnivore biomass [Stevens 2018: 542].

The distribution of soil phosphorus in the Serengeti, transported through AM symbioses and accelerated by migratory ungulates, may be a significant driver of plant diversity and ultimately mammalian carrying capacity (Anderson et al., 2007; McNaughton, Zuniga, McNaughton, & Banyikwa, 1997). Without AM fungal inputs of phosphorus, these nutrient diffusion gradients would undoubtedly decline [Stevens 2018: 543].

Stevens, Bo Maxwell, et al., 2018, Mycorrhizal symbioses influence the trophic structure of the Serengeti, Journal of Ecology 106: 536-546, 

For the full PDF version of the compendium issue where this article appears, visit Compendium Volume 2 Number 1 July 2018