There is little information about preferential competition for NH₄⁺ or NO₃^- among oaks and their adjacent annuals. Deciduous blue oak and white oak, and everygreen coast live oak were transplanted and cohabited for two years in a California oak woodland. Leaves of fifty selected oak seedlings were inserted into a small 2 ml vial containing 1.6 ml 1.0% ¹⁵N as (¹⁵NH₄)₂SO₄ or K¹⁵NO₃. Each oak species, along with one of each adjacent annual species of grass, forb and clover were sampled after 9-day-¹⁵N-labeling. Ectomycorrhizal colonization of oak roots was ~75% and arbuscular mycorrhizal colonization was ~30 for oak and annual plant species. Live oak biomass was double that of blue and white oak. However, white oak had significant higher total N content than live oak, and the latter than blue oak. After 9-day-¹⁵N-labeling, white oak had significant greater total ¹⁵N accumulation (5.7mg/plant) than both blue and live oak (3.5mg/plant), irrespective of ¹⁵NO₃^- or ¹⁵NH₄⁺ supplied. In contrast, root ¹⁵N accumulation in live oak was greater than that of other two oak species. Root ¹⁵N allocation was greater when ¹⁵NO₃^- was used, compared to ¹⁵NH₄⁺. In general, 45–50% of labeled ¹⁵N was remained in blue and live oak seedlings, while around 60% in white oak seedlings. The above results suggest that different oak species has distinctive ¹⁵NH₄⁺ or ¹⁵NO₃^- accumulation strategies. Meanwhile, leaf δ¹⁵N values of adjacent grass, forb and clover increased from 0.8~3.1‰ to 13~40‰ and to 10~40‰, no matter whether ¹⁵NH₄⁺ or ¹⁵NO₃^- was supplied and which oak species was surrounded, indicating that ¹⁵N has also been translocated to the adjacent annual plants through mycorrhizal interconnections and/or soil pathways. The possible mechanisms for nitrogen translocation among plants in oak woodlands might be through either mycorrhizal interconnections, soil pathways, or both.