Does helimulching after severe wildfire affect soil fungal diversity and community composition in a Mediterranean ecosystem?

Straw helimulching was applied to an area with a high soil erosion risk one month after the Navalacruz megafire (Iberian Central System, Ávila, Spain) to mitigate soil erosion and to maintain soil quality. To determine whether the soil fungal community, which is key to soil and vegetation recovery after fire, is altered by straw mulching, we examined the effect of helimulching one year after its application. Three hillside zones were chosen with two treatments in each zone (mulched and non-mulched plots), with three replicates of each treatment. Chemical and genomic DNA analyses of soil samples from mulched and non-mulched plots were performed to assess the soil characteristics and the soil fungal community composition and abundance. The total fungal operational taxonomic unit richness and abundance did not differ between treatments. However, there was an increase in the richness of litter saprotrophs, plant pathogens and wood saprotrophs associated with the application of straw mulch. The total fungal composition of mulched and non-mulched plots differed significantly. Fungal composition at the phylum level correlated with the soil potassium content and marginally with the pH and phosphorus content. The application of mulch promoted the dominance of saprotrophic functional groups. Fungal composition according to guilds was also significantly different between treatments. As conclusion, the application of mulch could mean a faster recovery of saprotrophic functional groups that will be responsible for decomposing the available dead fine fuel.