Temperature priming and memory in soil filamentous fungi

Most soil fungi experience a constantly fluctuating environment, and coping with resulting biotic and abiotic stressors can come at a considerable metabolic cost. We know that organisms respond better to severe stresses (triggering stress) when they have experienced a similar milder stress (priming stress) before. Asking how long organisms can remember a priming event is a compelling question. We here studied priming by temperature stress in filamentous fungi isolated from the same grassland soil. We hypothesized that filamentous fungi can show priming responses, and that their memory-spans correlate with their growth rates. Fungal colonies of 19 different filamentous fungi were first primed at 35 degrees C for 5 h (as priming stress) and after 0, 6, 12, 24 or 48 h they were exposed to 40 degrees C for 10 h (as triggering stress). The variable lag time between the stress applications allowed us to assess memory. Our main response variable was growth rate. Of the 19 fungal isolates tested, eight showed temperature priming ability. The Mucoromycotina isolates (Mortierellales) showed a mean growth increase following triggering stress that was 2.75-fold higher than in unprimed colonies (log-response-ratio). Mucoromycotina isolates had a memory half-life span (power-law-relationships) of 5.65 h. Considering fungal traits like growth rate to predict priming responses, we found a positive relationship between priming response (with 12 h memory phase) and growth rate. The differential ability to be primed in co-occurring isolates may have direct consequences for fungal communities and coexistence in soil. (C) 2016 Elsevier Ltd and British Mycological Society. All rights reserved.