Spatial variability in mycorrhizal hyphae and nutrient and water availability in a soil-weathered bedrock profile

We documented the spatial distribution, abundance and molecular diversity of mycorrhizal hyphae and physical and chemical properties of soil-weathered bedrock in a chaparral community that experiences seasonal drought. Because plants in this community were known to rely on bedrock-stored water during the summer, the data were used to evaluate the potential role of mycorrhizal hyphae in accessing bedrock-stored water during summer drought. The granitic bedrock was characterized by factures filled with a disaggregated, sandy loam that acted as conduits for water, and matrices composed of soil-weathered granite that retained the fabric and structure of rock. Mycorrhizal hyphae of six ectomycorrhizal taxa (from the Basidiomycota and Ascomycota), and arbuscular mycorrhizal hyphae (Zygomycota) were recovered from both fracture and matrix compartments to depths greater than 200 cm. Our findings also indicated a potential linkage between the abundance of Ascomycete hyphae, substrate physical (bulk density) and chemical properties (total N, N:P, Ca:Mg), and bedrock moisture content, as well as spatial patterning between hyphae and resources at a scale of 25–45 cm. Such linkages suggest that mycorrhizal fungal hyphae may be part of an adaptive mechanism that enables chaparral plants to survive seasonal drought.