PARENT SESSION
Oral Session # 81: Soil Ecology II: Microorganisms and Mycorrhizae.
Presiding: SJ Hall
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 106.

Belowground N transfer among plants in a California oak woodland.

He, Xinhua², Horwath, William¹, Bledsoe, Caroline¹, Zasoski, Robert¹, Idol, Travis¹, ² University of California at Davis, Davis, CA¹ University of California at Davis, Davis, CA

ABSTRACT- Movement of soil resources among plants through common mycorrhizal networks (CMNs) in the field has received less attention. We examined nitrogen (N) movement among different species of trees and grasses that had either ectomycorrhizae or arbuscular mycorrhizae in a California oak woodland. The experiment consisted of 3 tree pairs with foothill pine (Pinus sabaniana) being a N donor and receiver plants consisting of foothill pine, blue oak (Quercus douglasii) or buck brush (Ceanothus cuneatus). We foliarly applied an ¹⁵-NNO₃^- solution to isotopically label the pine donor. We collected leaf samples from all trees and grasses between the trees weekly for one month following ¹⁵NO₃^- labeling, and tree root samples at 4 weeks. Samples were analyzed for ¹⁵N content. Leaf ¹⁵N values at week-zero were 2.37, 2.22, -0.12 and 2.51%0 (per mil) in pine, oak, ceanothus and grasses, respectively. After 4 weeks, leaf ¹⁵N values increased to 45.69%0 in the donor pine and 5.72%0 in receiver pine, to 6.16, 3.70 and 8.12%0 in the oak and ceanothus receivers and grasses, respectively. Root ¹⁵N values were 10.36, 14.05 and -0.13 %0 for the control of pine, oak and ceanothus, and increased to 29.52%0 in the donor pines, and to 20.84, 19.11 and 8.04%0 for the receiver pine, oak, ceanothus, respectively. Transfer of ¹⁵N from the donor tree roots to the receiver tree roots and grasses occurred at an appreciable rate and amount regardless of the tree pair. Since some these tree pairs and grasses had different ectomycorrhizae or arbuscular mycorrhizae, direct transfer of N probably did not occur. The enrichment of grasses suggests the root N of the donor tree leaked into the rhizosphere before being translocated among the receiver trees and grasses. The similar ¹⁵N increase of the receiver tree roots compared to their respective controls suggests that CMNs play an important role in competing and distributing root N among plants.

Key words: common mycorrhizal networks (CMNs), grasses, ¹⁵N , pine, oak, ceanothus