Performance of Taxonomically Diverse Native Isolates of Mycorrhizal Fungi in Symbiosis with Young Grapevines

Abstract

Grapevines rely on arbuscular mycorrhizal fungi (AMF) to obtain ample phosphorus (P) from soils with low to moderate P like the Ultisols of western Oregon. Prior research indicated that nine species, or virtual taxa, of AMF colonized the roots of ‘Pinot noir’ at greater than 1% abundance in a single vineyard. However, little is known about how different taxa within a community vary in their capacity to function as symbionts with grapevines. The effectiveness of five native AMF species representing five genera to promote growth and nutrient uptake of ‘Pinot noir’ was examined in a fumigated Ultisol soil under well-watered and periodically dry conditions. Plants were grown with each of the different isolates alone or without AMF. After 8 and 16 weeks, whole vines were destructively harvested and biomass and nutrients were determined. Results showed that four of the isolates colonized roots extensively, increased root and shoot biomass, and predominantly increased P uptake. A Claroideoglomus isolate was superior in promoting shoot growth as compared with Rhizophagus irregularis, even though both isolates increased P uptake to the same extent, suggesting a higher carbon cost for R. irregularis. Scutellospora calospora failed to colonize roots beyond a trace and had no impact on vine performance. The ability to increase P uptake among the four effective fungi was not related to the frequency of arbuscules in roots suggesting that some P exchange occurs via hyphae within the cortex, particularly for Funneliformis mosseae. Water limitation reduced P uptake as a main effect across all mycorrhizal treatments, suggesting that the native isolates studied here have similar functionality under well-watered and periodically dry conditions.