PARENT SESSION
Oral Session #22: Mycorrhizae and ecosystem function.
Presiding: A. Tuininga
Monday, August 5. 1:00 PM to 3:45 PM. Grand Ballroom East, Radisson.
Does N utilization in ericoid association reflect the intraspecific variation in N source preference by Hymenoscyphus ericae.
GRELET, Gwen-Aelle*,1, MEHARG, Andrew1, ALEXANDER, Ian1, 1 University of Aberdeen, Aberdeen, GB
ABSTRACT- N-limited heathland are dominated by shrubs such as Vaccinium, or Calluna, which are thought to rely on ericoid mycorrhizae for N acquisition. Genetic diversity in such ericoid fungi is high, even in single host-root systems. We tested if genetic diversity, (1) corresponds to functional diversity in N source(s) utilisation by the fungus, and (2) enables the plant/fungus association to maximise exploitation of N. Five isolates of Hymenoshyphus ericae were grown axenically to compare their growth response to C limitation and forms of N. Three strains were selected for differences in N utilisation and used to inoculate sterile seedlings of Vaccinium macrocarpon and V. vitis-idaea. These were grown in sterile microcosms for five months with N added as either ammonium, nitrate or glutamine. A subset of microcosms were then supplied with 15N- labelled N for 2 days, before being harvested, and shoot, root biomass, N content and shoot 14/15N ratio determined. Mycorrhizal infection was beneficial only to V. macrocarpon, irrespective of the mycorrhizal strain. In both species, growth responses depended on the form of N supplied but not on the strain. 15N uptake and transfer to plant shoot by the different strains depended on the host plant, and on the N source. Differences were found between strains but these did not correlate with differences previously found in liquid culture. This work questions the relevance of studying mycorrhizal fungi in isolation, or in symbiosis with a specific host, in order to assess their functional diversity and understand their role in ecosystems.
KEY WORDS: Genetic diversity, N-limited environment