Tian Tian* and R. Paul Schreiner
*University of California Cooperative Extension, 1031 South Mountain Vernon Avenue, Bakersfield, CA 93307 (titian@ucanr.edu)

Arbuscular mycorrhizal fungi (AMF) are symbiotic partners of grapevines and con- tribute to nutrient acquisition from soil. To understand whether AMF enhance vine nitrogen (N) uptake from organic sources of N, mycorrhizal and non-mycorrhizal Pinot noir plants were grown in soil with low N availability. Within each AMF group, vines were assigned to seven different N treatments, including no N addition, NH4NO3 applied at 3 or 6 mM N, glycine applied at 3 or 6 mM N, and leaf litter applied at 10 or 20 g. Vines were initially grown for four weeks with moderate N prior to the addition of different types of N. Shoot growth and root colonization by AMF were measured periodically, and vines were destructively harvested after nine weeks to determine biomass and nutrient uptake. Shoot biomass, root biomass, and vine N uptake were improved by each of the N sources tested, but AMF did not enhance vine N uptake in any case. Shoot growth was reduced by AMF when NH4NO3 was supplied at 6 mM N, but AMF did not alter shoot biomass in other N treatments. Root colonization by AMF increased in response to added N, irrespective of the type of N supplied. However, the frequency of arbuscules in roots declined in both litter treatments at nine weeks but remained high in the NH4NO3 and glycine treatments. Results indicate that AMF do not improve vine N uptake from organic N sources and can divert investment to shoot growth when inorganic N is supplied at a moderate rate.

Funding Support: USDA-ARS