Ectomycorrhizal fungi in a Northern California Quercus-Pinus woodland: Hyphal characterization and roles in carbon, nitrogen, and potassium transfers

The symbiotic ectomycorrhizal (ECM) relationship between trees and fungal associates in the Sierra Nevada Foothills of California may influence survival in the harsh Mediterranean climate. Several experiments evaluated the function and occurrence of ECM fungi associated with native trees in California's oak-pine woodlands. Studies focused on identifying fungal hyphae species present near mature trees, and nutrient cycling between hyphae and saplings as well as between paired saplings. To evaluate hyphal length and investigate the identity of ECM hyphae surrounding mature trees, nylon mesh bags filled with sand were buried within the top 10 cm of soil around Quercus douglasii, Q. wislizeni, Pinus sabiniana, or P. ponderosa trees. After one year, hyphae were extracted from the bags and hyphal length was measured by various techniques. Hyphal length measured by microscope images and line intersect method was the most efficient method. Molecular identification of hyphal species revealed Thelephoraceae and Boletaceae were common under both Quercus spp. and P. sabiniana; however, hyphal communities ultimately differed among tree species and overlapped somewhat with reported sporocarp and root tip communities at the same site. Nutrient transfer mechanisms between hyphae and P. ponderosa saplings were investigated by applying Rb and 15N-NH4 + to soil in a PVC hyphal chamber buried near the sapling. Nitrogen transfer to the saplings as determined by foliar delta15N levels throughout the year exhibited large variations. Greatest Rb transfer occurred within 80 days. The following year, 15N-NH4 + was applied again to the chamber and 13C-CO 2 was applied to the sapling. Analysis of harvested saplings, soil, and chamber found elevated 15N levels in all components. Carbon (13C) transferred into sapling roots, rhizosphere soil, and hyphal tissues in chamber. Soil surrounding saplings and chambers were not enriched in 13C, which suggested hyphal mediated transfer. Sapling to sapling transfer of foliar applied 15N-NO3 - demonstrated high retention in donor needles and stems. Mycorrhizal colonization in receiver plants and 15N concentrations in neighboring forbs were negatively correlated. Uptake of 15N by herbaceous arbuscular mycorrhizal hosts occurred where N accessed was probably from rhizodeposits and hyphal turnover. Grasses and forbs accumulated more 15N than legumes.