Biocrusts are complex mosaics of algae, lichens, mosses, fungi, cyanobacteria, and other bacteria. Individually and collectively, biocrust organisms perform multiple ecosystem services, but little is know concerning interactions between constituents. One such proposed interaction is the fungal loop hypothesis where fungi wake up and hold N until larger water pulses allow plants to become active and use the sequestered N. To validate the potential movement of nutrients through fungal loops we created a small localized precipitation event and measured the translocation of 15N-NH4+ and 15N-NO3- within Microcoleus- and lichen-dominated crusts and a dominant grass species, Achnatherum hymenoides. We also measured the fungal constituents in the two crust types using quantitative PCR and target metagenomics of the 18S rRNA gene.
Within 24 hours, 15N-NH4+ traveled further than 15N-NO3- in Microcoleus-dominated crusts. Movement of 15N in moss-dominated crusts was limited, suggesting that lichen- and moss-dominated crusts may harbor greedier constituents utilizing N. Without a precipitation event to activate the grass, none of 15N was sequestered by the grass. The biomass of ascomycota species correlated with the distance the 15N-NH4+ isotope traveled in Microcoleus crusts, while there was no such correlation with basidiomycota or bacterial biomass. Further, metagenomics revealed that much of the fungal community was comprised of dark septate ascomycetes that may act as conduits for N. Our findings demonstrate that the first part of the fungal loop exists and fungi may act as conduits moving certain inorganic N forms among biocrusts constituents.