Hyphal-mediated transfer of nitrate, arsenic, cesium, rubidium, and strontium between arbuscular mycorrhizal forbs and grasses from a California oak woodland

Arbuscular mycorrhizal (AM) fungi colonize most plant species in the savannah/oak woodland ecosystem of the California Sierra Foothills. These fungi may form belowground linkages between plant root systems, potentially altering nutrient transfers. In a laboratory experiment with two-chambered pots where only AM fungal hyphae connected the chambers, we examined nutrient transfer between native plant species of grasses and forbs. Two separate chambers with plants were separated by a set of two stainless steel screens (25 mu m mesh) separated by a I cm air gap. These screens successfully restricted root growth but allowed hyphal coverage (15-100% of the area) of the screens. Nutrient transfers were monitored by applying nitrogen (N-15),arsenic (P analog), strontium (Ca analog), and cesium and rubidium (K analogs). The analogs and N-15 were applied to leaves of donor plants for 48 h. We observed transfer of N-15, As, Cs, and Rb from donor shoots to receiver shoots. Element transfers were not correlated with receiver biomass or donor concentrations. Transfers varied among the elements and plant combinations. Both Rb and Cs (K analogs) had the same pattern of transfer. Nitrogen was transferred in greatest amounts and between forbs and grasses, and grasses acted as a stronger sink for N. Forbs were generally the stronger sink for As. Fungal hyphae facilitated transfer among forbs and grasses, suggesting that they have a key role in nutrient transfer in California oak woodlands. (c) 2007 Elsevier Ltd. All rights reserved.