Sunday, 10 January 2016

Energetic arguments constraining complex fungal systems

Fungi are ubiquitous and ecologically important organisms that grow over the resources they consume. Fungi decompose everything from dead trees to dung, but whatever substrate they consume, fungi are obliged to spend energy on growth, reproduction, and substrate digestion. Many fungi also recycle their own biomass to fuel further growth. Within this overall framework, each fungal species adopts a different strategy, depending on the relative investment in growth, recycling, digestion and reproduction. Collectively, these strategies determine ecologically critical rates of carbon and nutrient cycling, including rates of decomposition and CO2 release. Crucially, a given fungus will encounter more of a resource if it increases its growth rate, and it will obtain energy from that resource more rapidly if it increases its investment in transporters and digestive enzymes. However, any energy that is expended on growth or resource acquisition cannot be spent on spore production, so fungi necessarily confront trade-offs between these three essential processes.
An example of a foraging fungal network
To understand these trade-offs we developed an energy budget model which uses a common energy currency to systematically explore how different rates of growth, recycling, and investments in resource acquisition affect the amount of energy available for reproduction, and how those trade-offs are affected by characteristics of the resource environment. Our model helps to explain the complex range of strategies adopted by various fungi. In particular, it shows that recycling is only beneficial for fungi growing on recalcitrant, nutrient-poor substrates, and that when the timescale of reproduction is large compared to the time required for the fungus to double in size, the total energy available for reproduction will be maximal when a very small fraction of the energy budget is spent on reproduction. You can read about this free under the title "Energetic Constraints on Fungal Growth" and it appears in the glamorously titled American Naturalist. Luke, Mark and Nick