Access to Ectomycorrhizal Fungi Improves Early Growth of Locally Adapted Valley Oaks (Quercus lobata)

Massimiliano Menczer, Dept. of Ecology and Evolutionary Biology and Institute of the Environment, University of California, Los Angeles

Anna Boog, Dept. of Ecology and Evolutionary Biology and Institute of the Environment, University of California, Los Angeles

Alayna Mead, Dept. of Ecology and Evolutionary Biology and Institute of the Environment, University of California, Los Angeles

Victoria L. Sork, Dept. of Ecology and Evolutionary Biology and Institute of the Environment, University of California, Los Angeles

Most forest soils contain an array of mycorrhizae that grow on the roots of trees and aid in their growth. A key question is how much do they aid in their grown. This study was designed to (1) investigate the effect of ectomycorrhizal fungi on early growth in oak seedlings and (2) assess whether oak seedlings are adapted to the mycorrhizae in the localities where their acorns were produced. Acorns of Quercus lobata were sourced from the UCSB Sedgewick Natural Reserve (SNR) located near Las Olivas in the Santa Ynez Valley of Santa Barbara Co., CA.  and the UC Berkeley Blue Oak Ridge Reserve, located northwest of Mount Hamilton in Santa Clara County, CA and grown in the greenhouse for two years. In June 2021, 2-yr-old saplings were outplanted into two fenced plots at SNR:  Half of the seedlings were isolated from the mycorrhizal network by sterilizing SNR soil and planting into the ground with mesh netting known to exclude mycorrhizae.  The other half were planted into non-sterilized soil and mesh netting cut with holes. After six months, , we found that local Sedgewick saplings had greater growth with than without the presence of the mycorrhizae.  In contrast, the transplanted seedlings from Blue Oak Ridge had worse growth with exposure to the mycorrhizae network compared to the seedlings excluded from the mycorrhizae. These experimental results provide evidence of local adaptation in valley oak saplings to the local mycorrhizae.