The function of common mycorrhizal networks on the transfer of nutrients between oak woodland plants of the Sierra Foothills, California

Almost all plant species in the oak woodland of the California Sierra Foothills are mycorrhizal and have the ability to form underground hyphal connections creating potential networks that provide nutrient movement among plants. Avoiding the soil pathway for nutrient transfer may benefit plants by reducing competition with other soil organisms. A series of experiments examined fungal mediated nutrients transfer between plants common to the oak woodland in settings that ranged from a laboratory growth chamber, to a greenhouse, and to the field. In each case, adjacent plants had their root systems separated by 25 μm stainless steel screen and a 1 cm air-gap in order to restrict nutrient movement between plants to passage through fungal hyphae. In a growth chamber, multiple nutrients were simultaneously examined by applying nitrogen (15N), As (P analog), Sr (Ca analog), Cs and Rb (K analogs) to the leaves of plant groups consisting of forbs, grasses, or a mixture of both. We observed transfer of 15N, As, Cs, and Rb from donor shoots to receiver shoots. Nitrogen transfer was greatest between forbs and grasses. Grasses acted as a stronger sink for N. Forbs were generally a stronger sink for As. In the greenhouse, annual and perennial plant pairs consisting of an annual grass, a perennial grass, and an oak seedling were used as donors and receivers labeled with 15N and Rb at three annual grass life stages (vegetative, flowering, and senescing). Transfer for both 15N and Rb was greatest at the flowering and senescing growth stages. Perennial receivers accumulated 15N only in roots at all annual growth stages, whereas the annual grass accumulated Rb in both shoots and roots. In the field, oak seedlings were established in plots for 3 years prior to labeling with 15N and Rb. Transfers were not correlated with proximity to the donor, or with receiver biomass. We found that fungal mediated transfer of nutrients between oak woodland plant species occurs and is variable with nutrient type, and plant phenology. Transfers within the field were spatially variable, which may reflect a heterogeneous fungal connectivity within the soil environment.