Many dryland plants form synergistic relationships with arbuscular mycorrhizal fungi (AMF) providing phosphorus and other services in exchange for photosynthetically fixed carbon. Alongside AMF, Biological soil crusts (biocrusts), soil surface communities of mosses, lichen and cyanobacteria, often have positive effects on soil surface stability, as well as soil water and nitrogen retention. Biocrusts may also interact with plants through mycorrhizal networks. Understanding the degree and extent to which biocrusts support AMF will help unravel interactions among plants, biocrusts and AMF. We set up multiple bioassay studies to compare the AMF propagule density of biocrusts, bare soils and plant rhizosphere soils in six dryland ecosystems in the Western U.S. and Spain. Surface sterilized organic corn (Zea mays) was added to replicate pots with a band of live soil, sterilized soil, or biocrust. Six weeks after germination roots and shoots were separated, weighed, and processed for biomass. Root subsamples were stained to assess relative abundance of viable AMF propagules. We hypothesized that: (a.) AMF propagule abundance would be highest in rhizosphere soil, compared to biocrust or bare soil. (b.) Interactions with AMF would vary depending upon biocrust type, soil type and climate.
Results/Conclusions
Rhizosphere soil did not have higher colonization than other soils (p > 0.05). We found differences in AMF colonization of corn roots grown in biocrust and non-biocrust soil across our study sites and biocrust types within study sites for two of the six sites (Spain, p < 0.0001; Grand Staircase, p = 0.004), and greater arbuscule abundance (exchange structures) in Spain (p = 0.007) and the Great Basin Desert (p = 0.02). Corn grown in biocrust soil had equal or greater biomass than corn grown in bare soil. We conducted principal components analysis (PCA) to illustrate relationships among site level climate and soil properties. PC1 corresponded with 50% of the variation and separated drier sites with less plant cover and lower nutrient soils from higher precipitation sites with greater plant cover and more nutrient rich soils. In contrast, PC2 (25%) primarily reflected temperature differences between arid and semi-arid study sites. Patterns in AMF colonization and plant growth across our study sites did not match the PCA patterns. Next steps will be to assess functional aspects among biocrusts, vascular plants, and dryland ecosystems.